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Eating right for your brain

Although I’m a cognitive psychologist and consequently think that memory and cognition is mostly about your mastery of effective strategies, when it comes to age-related cognitive decline, I’m a big believer in the importance of diet and exercise. But while we know these things can play an important role in why some people develop cognitive impairment and even dementia as they age, and others don’t, we don’t yet know with any great certainty exactly what exercise programs would be the best use of our time, and what diet would have the most benefit.

The role of diet in fighting age-related cognitive decline is quite complex. Many older people have inadequate diets, partly no doubt because of the shrinking in appetite and perhaps the dulling of taste and smell. It seems to me, for example (and this is purely a casual observation), that sweet foods tend to be appreciated more by the elderly, while other flavors are less able to be appreciated. The problem with the shrinking appetite is that it becomes even more vital, if the quantity of food is much reduced, that the nutritional quality is good. The less you eat, the less you can afford to eat “empty calories”. Everything must count.

Other factors concern the need to fight declining physical health. Cardiovascular problems, cholesterol problems, blood pressure problems, inflammation — all these have been implicated in contributing to cognitive decline. Therefore any diet that helps you fight these problems is also helping you fight cognitive decline.

A recent Swedish study tackled the inflammation problem. The study, involving 44 overweight people aged 50-75, found that after four weeks eating foods presumed to reduce low-grade inflammation, bad (LDL) cholesterol was reduced by 33%, blood triglycerides by 14%, blood pressure by 8% and a risk marker for blood clots by 26%. Memory and cognitive function was also improved (but no details on that were reported, and at present it appears only a press release is available — no academic paper).

The diet was high in antioxidants, low-GI foods (i.e. slow release carbohydrates), omega fatty acids, wholegrain products, probiotics and viscous dietary fibre. Examples of foods eaten were oily fish, barley, soy protein, blueberries, almonds, cinnamon, vinegar and a certain type of wholegrain bread. Some of the products are not yet available in the shops, but were developed specifically for the study.

Another study, involving 712 New Yorkers, found that those who most closely followed a Mediterranean-like diet over a six-year period, were 36% less likely to have brain infarcts compared to those who were least following the diet. Such a diet has also been associated with a lower risk of Alzheimer's disease.

The Mediterranean diet includes high intake of vegetables, legumes, fruits, cereals, fish and monounsaturated fatty acids such as olive oil; low intake of saturated fatty acids, dairy products, meat and poultry; and mild to moderate amounts of alcohol.

And an 11-year study of over 3800 seniors found that those who adhered more closely to an anti-hypertension diet (DASH) maintained their cognitive performance better over time, and that this appeared due to intake of four food groups: vegetables, whole grains, low-fat dairy, nut/legumes.

Other studies have pointed to the importance of maintaining blood sugar levels.(These studies, with the exception of the Swedish study, are all ones that have been previously reported on this site.)

We can be fairly sure that fighting inflammation, hypertension, and so on, help us fend off cognitive decline and impairment in our senior years. We can also be reasonably sure that fruit and vegetables are good for us. No one’s arguing much about fish either (although you do have to consider the toxicity of the fish, especially mercury load). There’s a messy ground however over the whole carbohydrate, sugar, fat, protein, dairy ground.

Recently I read a very interesting article reviewing a new book called Good Calories, Bad Calories. In this book, the author apparently “dispels nearly every belief doctors and the public health community hold to be true about nutrition and health”. According to the blogger, “It would be easy to dismiss his claims, except that he makes his case not with theories and conjectures, but through a meticulous review of the nutrition and medical literature going back a hundred years.” Moreover, the claims do help explain some of the more puzzling quandaries about the rise of obesity.

They also, I have to say, fit in with my own experience.

The basic tenet of the book is that it is carbohydrates, and most especially refined carbohydrates, that are to blame for our current epidemics of obesity, diabetes, coronary heart disease, and even cancer. We should avoid anything made with flour, cereals, potatoes, and anything with a lot of sugar (bananas, I’m afraid, are also a no-no). We don’t, on the other hand, need to worry about meat, dairy, or fat.

This is, in fact, exactly what I have found in my own struggles with weight (although of course my reason for discussing this here is not weight per se but more fundamental physical problems). When my weight climbed to what I regarded as appalling levels, I lost the desired 20kg through a rigorous low-carbohydrate diet (although my reasons actually had more to do with trying to work through my food sensitivities). And when I say low-carbohydrate, I was actually living mainly on fruit and vegetables. I did find, after a while, that the lack of carbohydrate created an energy problem, but a quarter-cup (uncooked) of brown rice every day fixed that. When, after a couple of years, I loosened up on my diet, having some bread (gluten-free; yeast-free!), the occasional bit of baking, the occasional small bit of potato … well, my weight immediately started climbing again. I complain that I only have to look at some baking to add weight!

I’m fully conscious that this wouldn’t be everyone’s experience — I live with three males, all of whom are the tall, lean type, who can eat vast quantities of baking without it apparently having any effect. But this is my point. I think the author of this book makes some good points about the difficulties of diet research, and he may well be right in his recommendations. But even when we get to the point when we can be certain of what is a “healthy diet”, it’s still not going to be true for everyone.

So my advice to individuals is that you don’t take the disputes among health and nutrition experts as an excuse for eating what you like, but instead as a basis for exploration. Look at the various diets for which there is some evidence, and work out which ones work for you. Which will depend not only on your genetic makeup, but most particularly on the damage you’ve already done to your body (not pointing a finger! We’ve all damaged our bodies just by living). As a reminder of which I was interested to read  an interesting article in the New York Times on the high-fat diet recommended for  epileptics. 

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Total Cognitive Burden

Because it holds some personal resonance for me, my recent round-up of genetic news called to mind food allergies. Now food allergies can be tricky beasts to diagnose, and the reason is, they’re interactive. Maybe you can eat a food one day and everything’s fine; another day, you break out in hives. This is not simply a matter of the amount you have eaten, the situation is more complex than that. It’s a function of what we might call total allergic load — all the things you might be sensitive to (some of which you may not realize, because on their own, in the quantities you normally consume, they’re no or little problem). And then there are other factors which make you more sensitive, such as time of month (for women), and time of day. Perhaps, in light of the recent findings about the effects of environmental temperature on multiple sclerosis, temperature is another of those factors. And so on.

Now, I am not a medical doctor, nor a neuroscientist. I’m a cognitive psychologist who has spent the last 20 years reading and writing about memory. But I have taken a very broad interest in memory and cognition, and the picture I see developing is that age-related cognitive decline, mild cognitive impairment, late-onset Alzheimer’s, and early-onset Alzheimer’s, represent places on a continuum. The situation does not seem as simple as saying that these all have the same cause, because it now seems evident that there are multiple causes of dementia and cognitive impairment. I think we should start talking about Total Cognitive Burden.

Total Cognitive Burden would include genetics, lifestyle and environmental factors, childhood experience, and prenatal factors.

First, genetics.

It is estimated that around a quarter of Alzheimer’s cases are familial, that is, they are directly linked to the possession of specific gene mutations. For the other 75%, genes are likely to be a factor but so are lifestyle and environmental factors. Having said that, the most recent findings suggest that the distinction between familial and sporadic is somewhat fuzzy, so perhaps it would be fairer to say we term it familial when genetics are the principal cause, and sporadic when lifestyle and environmental factors are at least as important.

While three genes have been clearly linked to early-onset Alzheimer’s, only one gene is an established factor in late-onset Alzheimer’s — the so-called Alzheimer’s gene, the e4 allele on the APOE gene (at 19q13.2). It’s estimated that 40-65% of Alzheimer’s patients have at least one copy of this allele, and those with two copies have up to 20 times the risk of developing Alzheimer’s. Nevertheless, it is perfectly possible to have this allele, even two copies of it, and not develop the disease. It is also quite possible — and indeed a third of Alzheimer’s patients have managed it — to develop Alzheimer’s in the absence of this risky gene variant.

A recent review selected 15 genes for which there is sufficient evidence to associate them with Alzheimer’s: APOE, CLU, PICALM, EXOC3L2, BIN1, CR1, SORL1, TNK1, IL8, LDLR, CST3, CHRNB2, SORCS1, TNF, and CCR2. Most of these are directly implicated in cholesterol metabolism, intracellular transport of beta-amyloid precursor, and autophagy of damaged organelles, and indirectly in inflammatory response.

For example, five of these genes (APOE; LDLR; SORL1; CLU; TNF) are implicated in lipid metabolism (four in cholesterol metabolism). This is consistent with evidence that high cholesterol levels in midlife is a risk factor for developing Alzheimer’s. Cholesterol plays a key role in regulating amyloid-beta and its development into toxic oligomers.

Five genes (PICALM; SORL1; APOE; BIN1; LDLR) appear to be involved in the intracellular transport of APP, directly influencing whether the precursor proteins develop properly.

Seven genes (TNF; IL8; CR1; CLU; CCR2; PICALM; CHRNB2) were found to interfere with the immune system, increasing inflammation in the brain.

If you’re interested you can read more each of these genes in that review, but the point I want to make is that genes can’t be considered alone. They interact with each other, and they interact with other factors (for example, there is some evidence that SORL1 is a risk factor for women only; if you have always kept your cholesterol levels low, through diet and/or drugs, having genes that poorly manage cholesterol will not be so much of an issue). It seems reasonable to assume that the particular nature of an individual’s pathway to Alzheimer’s will be determined by the precise collection of variants on several genes; this will also help determine how soon and how fast the Alzheimer’s develops.

[I say ‘Alzheimer’s’, but Alzheimer’s is not, of course, the only path to dementia, and vascular dementia in particular is closely associated. Moreover, my focus on Alzheimer’s isn’t meant to limit the discussion. When I talk about the pathway to dementia, I am thinking about all these points on the continuum: age-related cognitive decline, mild cognitive impairment, senile dementia, and early dementia.]

It also seems plausible to suggest that the precise collection of relevant genes will determine not only which drug and neurological treatments might be most effective, but also which lifestyle and environmental factors are most important in preventing the development of the disease.

I have reported often on lifestyle factors that affect cognitive decline and dementia — factors such as diet, exercise, intellectual and social engagement — factors that may mediate risk through their effects on cardiovascular health, diabetes, inflammation, and cognitive reserve. We are only beginning to understand how childhood and prenatal environment might also have effects on cognitive health many decades later — for example, through their effects on head size and brain development.

You cannot do anything about your genes, but genes are not destiny. You cannot, now, do anything about your prenatal environment or your early years (but you may be able to do something about your children’s or your grandchildren’s). But you can, perhaps, be aware of whether you have vulnerabilities in these areas — vulnerabilities which will add to your Total Cognitive Burden. More easily, you can assess your lifestyle — over the course of your life — in these terms. Here are the sorts of questions you might ask yourself:

Do you have any health issues such as diabetes, cardiovascular disease, multiple sclerosis, positive HIV status?

Do you have a sleep disorder?

Have you, at any point in your life, been exposed to toxic elements (such as lead or severe air pollution) for a significant length of time?

Did you experience a lot of stress in childhood? Stress might come from a dangerous living environment (such as a violent neighborhood), warring parents, a dysfunctional parent, or a personally traumatic event (to take some examples).

Did you do a lot of drugs, or indulge in binge drinking, in college?

Have you spent many years eating an unhealthy diet — one heavy in fats and sugars?

Do you drink heavily?

Do you have ongoing stress in your life, or have experienced significant amounts of stress at some period during middle-age?

Do you rarely engage in exercise?

Do you spend most evenings blobbed out in front of the TV?

Do you experience little in the way of mental stimulation from your occupation or hobbies?

These questions are just off the top of my head, the ones that came most readily to mind. But they give you, I hope, some idea of the range of factors that might go to make up your TCB. The next step from there is to see what factors you can do something about. While you can’t do anything about your past, the good news is that, at any age, some benefit accrues from engaging in preventative strategies (such as improving your sleeping, reducing your stress, eating healthily, exercising regularly, engaging in mentally and socially stimulating activities). How much benefit will depend on how much effort you put into these preventative strategies, and on which and how many TCB factors are pushing you and how far you are along on the path. But it’s never too late to do something.

On the up-side, you might be relieved by such an exercise, realizing that your risk of dementia is smaller than you feared! If so, you might use this knowledge to motivate you to aspire to an excellent old age — with no cognitive decline. We tend to assume that declining faculties are an inevitable consequence of getting older, but this doesn’t have to be true. Some ‘super-agers’ have shown us that it is possible to grow very old and still perform as well as those decades younger. If your TCB is low, why don’t you make it even lower, and aspire to be one of those!

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Diabetes - its role in cognitive impairment & dementia

There was an alarming article recently in the Guardian newspaper. It said that in the UK, diabetes is now nearly four times as common as all forms of cancer combined. Some 3.6 million people in the UK are thought to have type 2 diabetes (2.8 are diagnosed, but there’s thought to be a large number undiagnosed) and nearly twice as many people are at high risk of developing it. The bit that really stunned me? Diabetes costs the health service roughly 10% of its entire budget. In north America, one in five men over 50 have diabetes. In some parts of the world, it’s said as much as a quarter of the population have diabetes or even a third (Nauru)! Type 2 diabetes is six times more common in people of South Asian descent, and three times in people of African and African-Caribbean origin.

Why am I talking about diabetes in a blog dedicated to memory and learning? Because diabetes, if left untreated, has a number of complications, several of which impinge on brain function.

For example, over half of those with type 2 diabetes will die of cardiovascular disease, and vascular risk factors not only increase your chances of heart problems and stroke (diabetes doubles your risk of stroke), but also of cognitive impairment and dementia.

Type 2 diabetes is associated with obesity, which can bring about high blood pressure and sleep apnea, both of which are cognitive risk factors.

Both diabetes and hypertension increases the chances of white-matter lesions in the brain (this was even evident in obese adolescents with diabetes), and the degree of white-matter lesions in the brain is related to the severity of age-related cognitive decline and increased risk of Alzheimer’s.

Mild cognitive impairment is more likely to develop into Alzheimer’s if vascular risk factors such as high blood pressure, diabetes, cerebrovascular disease and high cholesterol are present, especially if untreated. Indeed it has been suggested that Alzheimer’s memory loss could be due to a third form of diabetes. And Down syndrome, Alzheimer's, diabetes, and cardiovascular disease, have been shown to share a common disease mechanism.

So diabetes is part of a suite of factors that act on the heart and the brain.

But treatment of such risk factors (e.g. by using high blood pressure medicines, insulin, cholesterol-lowering drugs and diet control, giving up smoking or drinking) significantly reduces the risk of developing Alzheimer’s. Bariatric surgery has been found to improve cognition in obese patients. And several factors have been shown to make a significant difference as to whether a diabetic develops cognitive problems.

Older diabetics are more likely to develop cognitive problems if they:

  • have higher (though still normal) blood pressure,
  • have gait and balance problems,
  • report themselves to be in bad health regardless of actual problems (this may be related to stress and anxiety),
  • have higher levels of the stress hormone cortisol,
  • don’t manage their condition (poor glucose control),
  • have depression,
  • eat high-fat meals.

Glucose control / insulin sensitivity may be a crucial factor even for non-diabetics. A study involving non-diabetic middle-aged and elderly people found that those with impaired glucose tolerance (a pre-diabetic condition) had a smaller hippocampus and scored worse on tests for recent memory. And some evidence suggests that a link found between midlife obesity and increased risk of cognitive impairment and dementia in old age may have to do with poorer insulin sensitivity.

Exercise and dietary changes are of course the main lifestyle factors that can turn such glucose impairment around, and do wonders for diabetes too. In fact, a recent small study found that an extreme low-calorie diet (don’t try this without medical help!) normalized pre-breakfast blood sugar levels and pancreas activity within a week, and may even have permanently cured some diabetics after a couple of months.

Diabetes appears to affect two cognitive domains in particular: executive functioning and speed of processing.

You can read all the research reports on diabetes that I’ve made over the years in my new topic collection.

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Benefits of fruit & vegetables for cognition

  • Fruit & vegetables are a vital part of a brain-healthy diet.
  • Apart from valuable vitamins and minerals, they contain antioxidants which help protect against damage to brain cells, as well as helping with cholesterol and blood flow.
  • Color is your best sign that the fruit or vegetable has more 'goodness': go for reds and purples and dark greens.

I don't think anyone's going to try arguing that fruit and vegetables are not good for your health! We know they're good. But that's just general "oh, I know it's good for me" — do you know that the benefits are not only for your general health, your protection against obesity and diabetes, cancer and heart disease, but also for your brain. Actually, there's two aspects to this. An unhealthy diet (one rich in junk food, in saturated fat and sugar) is actively bad for your brain, and (the right) healthy diet is actively good for your brain.

Fruit and vegetables are only one part of a brain-healthy diet, of course, but they're a very important part. A major reason for this benefit is thought to lie in the antioxidants present in these foods. Antioxidants help fight the oxidative stress that increasingly damages our brain cells as we age. Antioxidants is a group term, and some that fall into this category are more important than others.

The anthocyanins appear to be the most useful — these are responsible for the reds, purples, and blues in some plants. Several studies have affirmed the cognitive benefits of blueberries and Concord grape juice in particular (Concord grapes are especially purple grapes). Basically, the darker the fruit, the more anthocyanins, and the more powerful it will be.

Other valuable compounds include pterostilbene (found in blueberries), and resveratrol (found in grapes and red wine), which lower cholesterol. Quercetin (found in apples, blueberries, and cranberries) protects against cell damage and apparently helps with blood flow.

All of this perhaps explains why it is so much better to eat well rather than hope to receive what you need from dietary supplements!

Of the vegetables, green leafy vegetables, especially spinach, have been found to be especially beneficial. Onions are also a good source of quercetin (and presumably red onions, like red apples, are better than their paler cousins).

As a rule of thumb, the best fruits and vegetables are those with the most color. And, obviously, it's the color you want to eat (so no peeling your nice red apple!).

References

See the news reports

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Lifestyle

Benefits of fish & oils for cognition

  • Regular consumption of fish, especially oily fish, is associated with a reduced risk of Alzheimer's and better cognitive performance in old age.
  • High levels of omega-3 oils are associated with less brain shrinkage, and less brain damage in old age.
  • The benefits of supplements (as opposed to deriving these oils from food) is less clear, with inconsistent findings. It seems likely that their benefits depend on the individual's health and genetic profile, as well as on the nature and type of supplement.

There have been quite a few studies looking into the possible benefits of omega-3 fatty acids and fish (a good source of the oils), particularly for older adults. Several large studies have found that regular intake of oily fish is associated with lower rates of dementia, and some evidence that eating fish regularly slows the rate of 'normal' age-related cognitive decline.

However, findings into the effects of omega-3 oils have not been consistent, and one reason for that may lie in its interactions with other factors. For example, B vitamins have been found to improved cognition in older adults, but only when omega-3 levels are high. A number of studies have found regular consumption of fish is associated with reduced Alzheimer's risk, but one study found that, although it  was associated with less Alzheimer's pathology, this was only in those with the 'Alzheimer's gene' (APOE4).

The same study found that fish oil supplementation was not associated with any differences in neuropathology — but higher levels of alpha-linolenic acid (an omega-3 fatty acid found in flaxseed, chia seeds, walnuts, etc) were associated with a reduced chance of brain infarctions. Another large study found that omega-3 supplements (fish-based, not plant), together with vitamins C, E, beta carotene, and zinc, had no effect on cognitive decline among older adults with age-related macular degeneration. But it was suggested that this may be because the participants were too old to benefit from them.

Among other groups, the question of whether supplements of omega-3 fatty acids can help memory and cognition has been even more contentious, with some studies showing a positive effect and others failing to find an effect.

My own take on this issue is that, like so many other things, it all depends on what you’re working with. The most important of these factors is surely diet — it would be unsurprising if supplements are only of benefit when the individual's diet is seriously deficient. It may also well be the case that genes are a factor. (I'm ignoring, but we shouldn't forget, that many of the studies are probably poorly done, for this is a problematic area and it is tricky to do well.) There does seem to be more evidence that a diet high in omega-3 oils is good, than that supplements are going to help. And the weight of the evidence certainly favors the importance of high omega-3 levels for older adults.

Although it's not yet clear which fatty acids are most important, one is definitely docosahexaenoic acid, or DHA. Salmon, mackerel, herring, sardines, and anchovies are all good sources (not, I am sorry to say, your standard fried fish from the chippie). Other sources include almonds, walnuts, soy, flaxseed oil, and eggs laid by chickens that eat DHA-supplemented feed.

 

 

References

See the news reports

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Benefits of herbs & spices for cognition

  • Two spices have been implicated in fighting Alzheimer's (and thus age-related cognitive decline): turmeric and cinnamon.
  • Two herbs have been implicated in fighting Alzheimer's as well as being linked to better cognitive performance: sage and lemon balm.
  • Another two herbs have also been linked to better cognitive performance: rosemary and peppermint.
  • For those who suffer from sleep or stress problems (both of which contribute to cognitive problems), there is some evidence that, in keeping with traditional beliefs, chamomile and lavender both have calming effects.

There hasn't been a lot of research into the effects of herbs and spices on cognition and the brain, unfortunately. But on the positive side, the risk of side-effects is very low, so we don't need a lot of evidence for it to be worth trying.

Spices

Probably the most researched of these substances is the curry spice turmeric, more specifically one of its components, called curcumin. This has been found to be a powerful antioxidant and anti-inflammatory, which affects the brain protein BDNF (involved in the creation of new neurons). Research also suggests it may be protective against amyloid plaques, and so help fight Alzheimer's.

These findings have had an effect on my own cooking — I habitually cook up a lot of vegetables in the wok for our evening meal, and I add turmeric to the mix (heating it, along with some other curry spices, in the oil before adding the veges), so I have turmeric most days. Cumin, by the way, is (notwithstanding the similarity in names) something completely different.

Another spice that may be helpful, and one that is even easier to add to your daily diet, is cinnamon. I’ve been happily generous with cinnamon on my breakfast ever since the first hints came out that cinnamon might help protect against Alzheimer’s (it’s not like it’s an ordeal to add cinnamon!). Now we have more evidence, with a finding that two compounds found in cinnamon —cinnamaldehyde and epicatechin — appear to help prevent tau tangles (one of the characteristics of Alzheimer’s).

Herbs

As for herbs, there's a researcher in Britain who takes an interest in herbs, and it's really solely down to him and his students that we have any idea about the effects of herbs on cognition. Because they're all from one lab, and because the studies are invariably quite small, and the issue difficult to study, we can't put too much weight on these findings. But, as I say, where's the harm?

Four herbs have been put forward as helpful for the brain. Sage and lemon balm seem to increase the activity of acetylcholine, and so may be helpful to protect against Alzheimer's. They have also been linked to better cognitive performance. The scent of rosemary (i.e. from essential oil) has also been linked to better cognition, as has drinking peppermint tea.

From a more indirect perspective, chamomile tea and the scent of lavender have both been linked to feelings of calmness, which might help those who suffer from sleep problems. Lemon balm has also been linked to greater feelings of calmness.

References

See the news reports

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Benefits of vitamins & minerals for cognition

  • Iron is important at all ages, and it seems clear now that iron deficiency can affect cognition long before anemia is diagnosed. However, too much iron may also increase Alzheimer's risk, so you need to steer a middle road.
  • Magnesium and zinc also seem to be important minerals for cognition, and zinc deficiency has been linked to Alzheimer's.
  • B vitamins, especially B12 and folate, are important to fight age-related cognitive impairment and Alzheimer's.
  • Vitamins C, D, and E, are probably also important in this fight.
  • Interactions need to be taken into consideration. Zinc may impact iron absorption; vitamin C may not be well absorbed if iron is not bound; the vitamins are more effective if omega-3 levels are high.

Let me start by saying that if you're healthy and are eating a good balanced diet, there should be no need for you to take supplements. I also want to emphasize that the best way of meeting your body's needs for certain vitamins and minerals is to get them from food. In some cases, for one reason or another, this may not be possible. For example, as a (mostly) vegan, I take iron and B12 supplements, to make up for these deficiencies in my diet. Elderly adults with small appetites may also find it hard to get all the nutrients they need from their diet.

What nutrients are important for brain health and cognition?

Minerals

Number one mineral for cognition, that goes right across the age groups, is iron. A number of studies have found that iron deficiency in children and adolescents is associated with lower scores of cognitive tests, and indeed, it may be that iron deficiency during infancy has long lasting effects on cognition. The effects on adults have been less studied, but there is some evidence that iron deficiency may be linked to poorer attention. What's worth noting is that the levels at which iron is "deficient" may be overstated. It now seems that negative effects occur long before a person is officially diagnosed with anemia.

Other minerals that may impact learning and memory are magnesium and zinc, although evidence is limited thus far. Magnesium deficits are common in industrialized countries, and increase with age. Vegetarians, adolescents, and older adults, are particularly at risk of zinc deficiency. An analysis of Alzheimer's has revealed that one type of the disease, which is found most commonly at a younger age (50- to early 70s) and typically shows itself first in language and number difficulties, is associated with a significant zinc deficiency.

Good sources of magnesium are dark green leafy vegetables, some nuts (especially almonds and cashews), beans, seeds and whole unrefined grains (especially buckwheat). Red meats, fish and grains are good sources of zinc.

Do bear in mind that it is not a case of "if some is good, more is better"! Having too much is not a good idea either; this is another reason why getting your vitamins and minerals from food rather than supplements is a good idea. Too much iron, in particular, has been linked to an increased risk of Alzheimer's. It has been argued that many neurodegenerative diseases are partly caused by poorly bound iron, and it is vital to consume nutrients which bind iron, such as brightly-colored fruits (especially purple) and vegetables — but not, perhaps, green tea, which does bind iron, but taking them at the same time seems to cancel out each other's benefits!

Just to complicate the matter further, there is evidence that zinc inhibits iron absorption. These complications suggest there is something in the idea that you need to consider food combinations.

Vitamins

Vitamins B, C, D, and E all seem to be important for cognition, mainly in relation to prenatal development and prevention of Alzheimer's and age-related cognitive impairment. A long-running study of older adults found that those with diets high in omega 3 fatty acids and in vitamins C, D, E and the B vitamins had higher scores on cognitive tests than people with diets low in those nutrients, and moreover that these were dose-dependent, with each standard deviation increase in the vitamin BCDE score ssociated with an increase in cognitive score. Additionally, they showed less brain shrinkage than those with lower intakes of these nutrients.

The B vitamins are often called the B-complex vitamins, and they are a messy sort of group. The main ones of interest for cognition are B12, folate, and choline. Again, most of the research has focused on prenatal development, and age-related cognitive impairment and dementia.

The importance of folate and B12 has a lot to do with homocysteine, which is produced in the body by the breakdown of a dietary protein called methionine. High levels of homocysteine have been linked to increased risk of Alzheimer's, stroke, and vascular dementia, and greater brain shrinkage. B-vitamins are required to convert homocysteine back to methionine, and high levels of homocysteine go hand in hand with low levels of B12 and folate. Diet isn't the only reason for increased levels of homocysteine; smoking has also been implicated. But the association between homocysteine and age-related cognitive decline is not straightforward — it appears that seniors with normal levels of vitamin B12 perform better if their folate levels are high, but when vitamin B12 is low, high levels of folate were associated with poor cognitive performance, as well as a greater probability of anemia. Vitamin B12 is often deficient in older people.

There is also some evidence that B12 is more effective in slowing cognitive decline if levels of omega-3 oils are high.

Folate is a water-soluble B vitamin found particularly in citrus fruit, green leafy vegetables, whole-wheat bread, water-soluble dried beans and peas; however, they are often destroyed by cooking or processing. In the United States, Canada and Australia, flour is fortified with folic acid. Vitamin B12 is naturally found in animal foods including fish, milk and milk products, eggs, meat, and poultry.

Among older adults, choline, particularly in conjunction with omega-3 fatty acids and uridine (not available from food), has been found to improve memory in those cognitively impaired. Top sources of choline are eggs, peanuts, and meat. Fish and soy are also good sources.

References

See the news reports

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Lifestyle

Food & Supplements

  • There is little evidence that dietary supplements or changes to the diet improve mental function in young, healthy people.
  • Changes in diet and dietary supplements may be beneficial to older adults, or those suffering from physical disorders, allergies, depression, stress, etc.
  • Despite the claims made for many supplements, we can't point unequivocally to any as beneficial. Whether they are of benefit does depend on whether you are lacking in some vitamin and mineral (e.g., Vitamin B12), so it is advisable to have your levels checked.
  • Food is safer, and the evidence does now seem clear that fruit and vegetables rich in anti-oxidants are of particular benefit.

A perennial topic in the arena of memory improvement is the question of “food for the brain”, and in particular, whether there are dietary supplements that can improve your mental abilities. While my own emphasis is improvement through development and practice of skills, I don’t dismiss the possibility of improvement through more physical means. I myself am a great fan of the “you are what you eat” principle. This is mainly because I suffer from multiple food sensitivities, so the consequences of food are very much a reality for me. That doesn’t mean I believe perfectly healthy people should obsess about their diet. There is another principle that is of great importance: we are all individuals.

For example, a year ago, I wrote of the effects of caffeine on memory, concluding that: “while caffeine may help older adults in the later part of the day, those with hypertension, diabetes, impaired glucose tolerance, or high homocysteine levels, would be wiser to avoid coffee, even if decaffeinated. In general, while caffeine may help you overcome factors that lower your cognitive performance, it does not seem that caffeine has any significant direct effect on memory, although it may well help you pay attention.”

So, caffeine is more helpful for some types of people than others, and is in fact contra-indicated for some. Moreover, the effects are different for those who are accustomed to a high caffeine intake, compared to those who only occasionally consume caffeine. And – here’s the real kicker – I also know from personal experience that the effects of caffeine are highly individual: I myself respond to caffeine not with the usual increased alertness, but in fact with decreased alertness. It makes me sleepy!

I do think there are physical factors of far greater importance than diet. Sleep is the obvious one. Individual differences don’t show up in the basic need to have enough sleep, and the right sort of sleep, to optimize brain functioning, but they do of course show up as regards how much sleep is right for us. That also, is something that changes with age, and, I imagine, health, throughout our lifespan.

Another physical factor which should be given due weight is exercise. While its effect is not as great as sleep (I don’t think anything rivals the importance of sleep!), I would give it more importance than diet because its effect is far more consistent. I don’t think anyone would fail to benefit mentally from increased physical fitness (which is not to say there isn’t a level of fitness beyond which no more mental improvement will occur).

Diet, on the other hand, depends a great deal on the individual. There is little evidence that dietary supplements or changes to the diet improve mental function in those who don’t suffer from any of the conditions which can adversely affect brain function — e.g., aging, physical disorders, depression, stress, etc.

In other words, if you are a relatively young person with no health problems, I suggest you concentrate on getting enough sleep and exercise, and learning and practicing effective memory strategies.

If you have any conditions which can adversely affect brain function I would also emphasize doing this! But, additionally, I do think there are foods and supplements you can take which may well significantly improve your brain function.

Which ones? Here we enter the area of individual difference. To find out what is effective for you, you should start with the research. What foods and supplements have been demonstrated to be effective in improving cognition?

Here we enter an area fraught with difficulty. News reports come out about foods and supplements all the time, and today’s world is filled with people hawking “health” products. How do we know what to believe?

The first thing, of course, is to ascertain whether the claims are backed up by research. But that’s not as easy as it sounds, because every seller of such products knows the importance of sounding as if research has proven the effectiveness of their product. (Actually, I automatically disavow any text which talks of research “proving” something. No researcher worth his salt would ever make such a claim.)

How do we determine the genuineness and reliability of the research? First, and most importantly, by assessing the source. For example, I only cite research from reputable academic journals, or academic conferences. I also give greater weight to research from researchers whose work I know of. Hopefully, by so doing, I also make myself a reliable source.

This is not, however, infallible, for even well-respected journals can make mistakes. For example, very topically, the truthfulness of a widely reported study of a nutritional supplement's effects on thinking and memory in the elderly has recently been cast into doubt (actually, this is a rather polite phrase for the comments now being made: “scientists who reviewed the paper had found the methods and statistical findings so unlikely that they wondered whether the study had actually been done”; "The statistics were not just implausible, they were impossible.")

Nevertheless, the very shock with which these questions are being raised demonstrates that, by and large, the system does work. We cannot expect certainty.

Having approved the source, the second thing to consider is the extent to which the research has been replicated. One study does not make an answer! It is indicative only. It is interesting.

Even a second study is little more than another support. Before we can say, “You know, I really think there’s something to this”, we need a number of studies building together from different angles.

So, a study showing that sage can help cognitive function in healthy young adults (there is indeed such a study) is interesting. Given that sage is easy to grow, and commonly consumed (one doesn’t need to worry about toxicity), I would go so far as to say, give it a try! But I wouldn’t give a lot of weight to the research until more studies had been carried out. (I would, however, happily drink sage tea everyday on the off chance, except it turns out – I really can’t believe this! – I’m sensitive to sage, too.)

On the other hand, for a product that is expensive, or has potential side-effects, I would wait for more evidence to come in before trying it. Okay, we’ve looked at the research, we’ve found the foods and supplements of potential benefit. What next?

Next, you look at your own particular problems.

For example, my main problem is food sensitivities. The first, most dramatic, thing I did to overcome my increasing mental sluggishness was: stop eating foods which turned out to be bad for me! After concentrating on that for a year or two, with my physical and mental problems much improved (but not gone), I turned my attention to the damage done to my body over the long period during which I was unaware of my food sensitivities. I now take B12, which I am sure has had a significant effect on my brain, and have recently started taking iron (as a woman of childbearing age). I also take other mineral supplements, principally to overcome deficiencies in my environment (New Zealand’s soil is deficient in a number of minerals), and lecithin (partly because of the deficiencies in my diet as a result of having to avoid certain foods).

The final step, once you’ve established the possible foods and supplements which are worth trying, is to see whether they are effective for you. Remember me and the coffee. What works for one doesn’t necessarily work for another (and may indeed be harmful). But don’t try everything at once! One at a time, and the most likely first.

So, what foods and supplements might be of benefit to your brain?

Most of the research into the cognitive benefits of diet and supplements has been concerned with seniors, with alleviating the effects of age on the brain. This is consistent with the belief that there is little, if any, benefit to be gained by young, healthy adults. Having said that, however, the following have been shown to be of benefit in at least one study:

  • creatine
  • sage
  • lemon balm
  • a diet high in soy products

Remember my comment about the reliability of single studies! However, since three of these four are all perfectly “natural” food items, there would be little danger in trying these out.

Several substances are worth mentioning as having been of particular interest to researchers for their potential benefits to brains suffering from the effects of age:

  • gingko biloba
  • ginseng
  • choline (lecithin)
  • vitamin B12
  • phosphatidylserine (PS)
  • acetyl-L-carnitine (ALC)
  • antioxidants (particularly vitamin E)

This article originally appeared in the May 2004 newsletter.

diet
Lifestyle

Preventing dementia: Diet & exercise

It's increasingly clear that eating a healthy diet can have a big impact on whether or not you develop dementia.

A study1 of nearly 2000 older adults has found that eating a Mediterranean diet was associated with less risk of developing mild cognitive impairment or of transitioning from MCI to Alzheimer's disease. The third with the highest scores for Mediterranean diet adherence had a 28% lower risk of developing MCI compared to the third with the lowest scores, and of those who already had MCI, those with the highest scores for Mediterranean diet adherence had a 48% less chance of developing Alzheimer’s.

Another, similar-sized study2, has found that those who adhered more strongly to a Mediterranean-type diet had a 40% risk reduction, and those who were very physically active had a 33% risk reduction of Alzheimer's -- doing both gave people a 60% reduction.

A Mediterranean-type diet is typically characterized by high intake of fish, vegetables, legumes, fruits, cereals and monounsaturated fatty acids; relatively low intake of dairy products, meats and saturated fats; and moderate alcohol consumption. Most of these components have been independently associated with reduced dementia risk. Let's look at them one by one.

Fruit & vegetables

A very large study3 of older adults found that those who ate fruits and vegetables daily reduced their risk of dementia by 30% compared to those who didn’t regularly eat fruits and vegetables. Another large, long-running epidemiological study4 found that those who drank three or more servings of fruit and vegetable juices per week had a 76% lower risk of developing Alzheimer’s disease than those who drank juice less than once a week. The benefit seemed greatest for those who carried the so-called “Alzheimer’s gene”.

This may not have anything to do with vitamin C. A five-year study5 involving nearly 3000 people has found that use of Vitamin C or E or both was not associated with a reduced risk of developing dementia or Alzheimer’s. However a study6 involving 4,740 elderly found the greatest reduction in both prevalence and incidence of Alzheimer's in those who used individual vitamin E and C supplements in combination. There was no significant benefit in these vitamins alone.

Of course, it is now well understood that taking vitamins as supplements is not the same as receiving them in food.

Two studies have come out in favor of a diet rich in foods containing vitamin E to help protect against Alzheimer's disease. One study7 involved 815 Chicago residents age 65 and older with no initial symptoms of mental decline, who were questioned about their eating habits and followed for an average of about four years. When factors like age and education were taken into account, those eating the most vitamin E-rich foods had a lower risk of developing Alzheimer’s, provided they did not have the ApoE e4 allele. This was not true when vitamin E was taken as a supplement. The effect of vitamin C was not statistically significant.

The other study8 involved 5,395 people in the Netherlands age 55 and older who were followed for an average of six years. Those with high intakes of vitamins E and C were less likely to become afflicted with Alzheimer's, regardless of whether they had the gene variation. This association was most pronounced for current smokers.

So beneficial effects of these vitamins may depend on genetics, smoking history, and possibly other lifestyle factors. But there are other valuable compounds common in fruits & vegetables. Another class of antioxidant chemicals, polyphenols, are now suspected. Polyphenols generally exist primarily in the skins of fruits and vegetables and are particularly abundant in teas, juices and wines.

A cell study9 also found that quercetin (a flavonoid with greater antioxidant and anticancer properties than vitamin C) protects against cellular damage. Quercetin is particularly abundant in apples (mainly in the skin, and especially the red ones). Other good sources are onions, blueberries and cranberries.

Another cell study10 found that compounds in blackcurrants (anthocyanins as well as polyphenols) strongly protect neuronal cells against the effects of amyloid-beta. Boysenberries contain the same compounds, and those that are darker are likely to be more potent.

The inconsistent findings regarding vitamins C and E may also have to do with the presence of folates. Data from the Baltimore Longitudinal Study of Aging11 revealed that although those with higher intake of folates, vitamin E and vitamin B6 had a lower risk of developing Alzheimer’s, statistical analysis showed it was only folate consumption that was significant. Those who had at least 400mcg of folates a day (the recommended daily allowance) had a 55% reduction in risk of developing Alzheimer’s. Unfortunately, most people who reached that level did so by taking supplements, suggesting the difficulty of doing so through diet alone.

Folates are abundant in foods such as liver, kidneys, yeast, fruits (like bananas and oranges), leafy vegetables, whole-wheat bread, lima beans, eggs and milk; however, they are often destroyed by cooking or processing.

The benefits of folates probably has to do with its effect on homocysteine. A mouse study12 indicates that increased levels of homocysteine are produced by low intake of folate and B vitamins, and impair cognition through microvascular changes. 

High levels of homocysteine are associated not only with deficiencies in vitamin B12 and folate, but also with smoking.

High levels of homocysteine were associated in one study13 with a more than five-fold increase in the risk for stroke, a nearly five-fold risk for vascular dementia, and almost triple the risk for Alzheimer's disease. Findings from the long-running Framingham study14 found people with elevated levels of homocysteine in the blood had nearly double the risk of later developing Alzheimer’s disease.

Moreover, evidence from a study15 using genetically engineered mice suggests that increased levels of homocysteine in the brain cause damage to nerve cells in the hippocampus -- which can be repaired when there is an adequate amount of folate, but not when there is a deficiency.

Omega-3 oils & fish

One of the clearest findings in this area has been the benefits of regularly consuming omega-3 oils, fish oil, and fish. Several epidemiological studies have indicated that regularly eating fish (at least once a week) reduces risk of dementia. More recently, two very large studies have come out in support. One very large study3 of older adults found that those who regularly consumed omega-3 rich oils, such as canola oil, flaxseed oil and walnut oil, reduced their risk of dementia by 60% compared to people who did not regularly consume such oils. Additionally, those who ate fish at least once a week had a 40% lower risk of dementia -- but only if they did not carry ApoE4 gene.

Moreover, for those who didn’t have the gene, regular use of omega-6 rich oils, but not omega-3 rich oils or fish, were twice as likely to develop dementia compared to those who didn’t eat omega-6 rich oils (e.g., sunflower or grape seed oil).

The second study16 comes from the famous long-running Framingham Heart Study, which found that those with the highest levels of DHA (an omega-3 polyunsaturated fatty acid found in relatively high concentrations in cold-water fish) had a 47% lower risk of developing dementia. Those with these levels tended to eat an average three fish servings a week, as well as an average of .18 grams of DHA a day. Those at lower levels ate markedly less fish.

There is also some suggestion that omega-3 oils might help slow the progression of dementia. A Swedish study17 found that, although fatty acids DHA and EPA didn't slow cognitive decline in those with mild-to-moderate Alzheimer’s, they did slow decline in those with very mild cognitive impairment (a frequent precursor of dementia). It's been suggested that anti-inflammatory effects are an important reason for the benefit, why might explain why benefits only occur in the very early stages, when levels of inflammation seem to be higher.

Similar results were more recently reported18 from a large 18-month trial. This one, however, suggested that genetic status might be a factor -- that those without the “Alzheimer’s gene” ApoE4 might benefit even if impairment had progressed to mild-to-moderate Alzheimer’s.

There are a number of reasons why DHA might help brains.

A study involving genetically engineered mice19 has found that a diet high in DHA dramatically slowed the progression of Alzheimer's by cutting the harmful brain plaques that mark the disease. An earlier study20 showed that DHA protected against damage to the synaptic areas where brain cells communicate and enabled mice to perform better on memory tests. More recent research21 has revealed that DHA increases the production of LR11, a protein that is found at reduced levels in Alzheimer's patients and which is known to destroy the protein that forms the plaques associated with the disease.

Food sources of omega-3 fatty acids include fish such as salmon, halibut, mackerel and sardines, as well as almonds, walnuts, soy, flaxseed, and DHA-enriched eggs. These fish have high levels of DHA because they consume DHA-rich algae. Because these fishes' oiliness makes them absorb more mercury, dioxin, PCP and other metals, a less risky yet more costly strategy is to consume fish oil or purified DHA supplements made from algae.

Possible benefits of wine, tea, and coffee

There have been a number of reports that moderate alcohol consumption (generally defined as 1 drink or less per day for women and 1-2 drinks or less per day for men) may help reduce your risk of developing dementia, and a 2008 review of 44 studies22 supported this conclusion. 

However, given that alcohol has known negative effects on the brain, no one is recommending that non-drinkers take up the habit! All one can say is that there's no reason to alter your habits if you are a moderate drinker. On the other hand, if you drink more than this, you are probably best to knock it back to this level.

However, the evidence suggests that it is wine rather than alcohol in general that is beneficial for the brain. A large Danish study23 found that those who drank wine occasionally in the 1970s had a lower risk of developing dementia in the 1990s (when participants were 65 or older). However, occasional beer drinking was associated with an increased risk of developing dementia. But we cannot draw too hard & fast a conclusion from this, as eating habits were not investigated, and research suggests that wine drinkers may have better dietary habits than beer and liquor drinkers. Moreover, a very large study of older adults3, that found a significant effect of some dietary factors, found no effect of wine.

There are, however, some good reasons for believing regular drinking of red wine may help the aging brain. Red grapes contain several polyphenols that have been shown to significantly reduce cognitive deterioration in genetically engineered mice, by preventing the formation of amyloid beta. One of these is resveratrol; the others are catechin and epicatechin. Resveratrol was much vaunted when its effects were first discovered, but unfortunately it requires extremely high doses. The more recent discovery24 of the catechins is much more exciting, as they appear to be effective at much lower doses. The catechins are also abundant in tea and cocoa.

Tea, most particularly green tea, has also been found25 to inhibit the activity of enzymes associated with the development of Alzheimer's Disease. Green tea also obstructed the activity of beta-secretase.

These inhibitory properties were not found in coffee. However, a large, long-running Finnish study26 has found that those who were coffee drinkers at midlife had lower risk for dementia and Alzheimer’s later in life compared to those drinking no or only little coffee midlife. The lowest risk was found among moderate coffee drinkers (drinking 3-5 cups of coffee/day).

Restricting your calories

There has been some talk that calorie-restricted diets might help prevent Alzheimer's. So far, the only indications have come from experiments with genetically engineered mice. While there have been a number of studies providing evidence that high cholesterol, obesity, and other cardiovascular risk factors increase the likelihood of Alzheimer’s, it is decidedly premature to say whether calorie-restricted diets would benefit humans. Particularly since one of the early signs of Alzheimer's is weight loss. So it is certainly not recommended that people severely restrict their diets. More useful is removing certain food types (e.g., the "bad" oils; sugar -- there is some evidence that Alzheimer's may be a type of diabetes), and increasing consumption of others (fish, "good" oils, fruit & vegetables).

There may also be a genetic link. A four-year study27 of nearly 1000 older adults found that among those who carried the ApoE e4 gene, those who consumed the most calories had a 2.3 times greater chance of developing Alzheimer’s compared to those who ate the fewest calories. But calories weren't a factor for those without the gene.

Cholesterol

A study28 involving nearly 10,000 people who underwent health evaluations between 1964 and 1973 when they were between the ages of 40 and 45, has found that those with total cholesterol levels between 249 and 500 milligrams were one-and-a-half times more likely to develop Alzheimer's disease than those people with cholesterol levels of less than 198 milligrams. People with total cholesterol levels of 221 to 248 milligrams were more than one-and-a-quarter times more likely to develop Alzheimer's disease. High cholesterol increased risk regardless of midlife diabetes, high blood pressure, obesity, smoking and late-life stroke.

A review29 of autopsy cases of patients over 40 years old found that high blood cholesterol levels were correlated with the presence of amyloid deposits in the brain in the youngest subjects (aged 40-55).

An analysis30 of data on 1037 older women who had participated in a clinical trial of hormone replacement therapy found that high cholesterol levels increase the risk of cognitive impairment.

A large-scale Finnish study31 following 1449 men and women over 21 years found that raised systolic blood pressure and high serum cholesterol concentration, particularly in combination, in midlife, increase the risk of Alzheimer's disease in later life. Raised diastolic blood pressure had no significant effect.

However, the long-running, large-scale Framingham Heart study32 found that, after adjustment for age, sex, APOE genotype, smoking, body mass index, coronary heart disease, and diabetes, there was no significant association between AD risk and cholesterol level.

Previous studies suggesting that fat may be involved in the development of dementia and Alzheimer’s disease have been contradicted by a new study33 involving over 5,000 elderly people over a period of six years. The study found no correlation between fat and cholesterol intake and risk of dementia, and no evidence for a reduction in risk for those taking cholesterol lowering medication.

A cell study34 provides more understanding of why there might be a link between cholesterol and Alzheimer's disease. The study found that proteins which help control cholesterol levels in arterial walls were also present in neurons, and when the genes for these proteins were over-expressed, production of amyloid beta protein fell. The finding suggests a new approach to slowing Alzheimer’s. The study also showed that the apoE protein is extremely good at regulating cholesterol removal from neurons — the gene for this protein is a well-known genetic risk factor for Alzheimer's.

Diabetes

A large Swedish study35 has found that men with low insulin secretion capacity at age 50 were nearly one-and-a-half times more likely to develop Alzheimer’s disease than men without insulin problems. The risk was strongest in those who didn't have the APOE4 gene. Another large study36 found that diabetes was related to a significantly higher risk of developing amnestic mild cognitive impairment in older seniors (average age 76), after controlling for other risk factors. And a large study37 of post-menopausal women (mean age 67 years) found that those with poor blood sugar control were four times more likely to develop MCI or dementia. Findings38 from the long-running Religious Orders Study also support a link between diabetes and an increased risk of developing Alzheimer's disease.

Evidence from a mouse study39 suggests that diabetes might increase risk because elevated blood glucose levels interact with beta amyloid in a way damaging to blood vessels in the brain. In fact it has been suggested that Alzheimer’s could be considered a third form of diabetes. Another study40 provides evidence that amyloid oligomers remove insulin receptors from nerve cells, rendering those neurons insulin resistant. Another mouse study41 suggests that low levels of insulysin, an enzyme that degrades insulin, are a factor. The enzyme, it seems, also degrades amyloid-beta peptides, and even a partial decrease in insulysin activity was found to raise amyloid-beta peptide levels in the brain.

Obesity

A review42 of 10 international studies published since 1995, covering just over 37,000 people, has found that obesity increased the relative risk of dementia by an average of 42% compared with normal weight. Being underweight increased the risk by 36%. For Alzheimer's Disease and vascular dementia, specifically, obesity was an even more significant risk: 80% and 73%, respectively. With regards to Alzheimer’s, obesity was more likely to be a risk factor for women, but men were more affected when it came to vascular dementia.

A very large study43 that measured abdominal fat at age 40 to 45 and dementia occurrence some 36 years later, found that those with the highest amount of abdominal fat were nearly three times more likely to develop dementia than those with the lowest amount of abdominal fat. Having a large abdomen increased the risk of dementia regardless of overall weight and existing health conditions, although being obese as well did increase the risk. Those more likely to have abdominal obesity, were women, non-whites, smokers, people with high blood pressure, high cholesterol or diabetes, and those with less than a high school level of education. And another large study44 found that those who at 40 were obese, or had high blood pressure, or high cholesterol levels, were twice as more likely to develop dementia by the age of 60. Having all three of these risk factors increased their chances six-fold.

And just to be really scary, when45 genetically engineered mice were fed a diet rich in fat, sugar and cholesterol for a mere nine months (although that is, of course, much longer for a mouse than it is for us!), they developed a preliminary stage of Alzheimer's pathology in their brains, suggesting that a ‘fast food’ diet could be a contributory factor in those with the Alzheimer’s gene.

Physical exercise & fitness

A number of studies have found that physical fitness reduces the risk of dementia. One way physical exercise can help fight dementia is through its ability to grow neurons in the hippocampus. This is well-established in rodent studies, and has been confirmed in small human studies. One such study46 found the association between physical fitness and hippocampus size was specifically associated with performance on certain spatial memory tests. Another47 found that those with early Alzheimer's disease who were less physically fit had four times more brain shrinkage when compared to normal older adults than those who were more physically fit, suggesting the value of physical fitness extends to slowing down the progression of the disease.

Another reason for exercise to prevent dementia is through its effect on cardiovascular fitness, and a reasonably large four-year study48 did indeed find that the most active (top third) were significantly less likely to develop vascular dementia than the least active (bottom third). Interestingly, no such association was found with Alzheimer’s disease. However, at least two large studies have found a significantly reduced risk of dementia in those who had higher levels of fitness49 or exercised three or more times a week50. It may be that exercise has a greater effect on vascular dementia, but many cases of Alzheimer's dementia are actually mixed dementia, with a vascular component.

References
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