Healthy eating and the brain

Introduction

The impact on the body of what we eat and drink is well recognised in the popular and scientific press and has recently been the focus of several TV programmes. But the link between diet and brain health is less well recognised.

Yet the same healthy balanced diet that is widely recommended to reduce a person’s risk of developing coronary heart disease, strokes, some cancers and diabetes is also relevant to good brain health.

The introduction to this booklet refers to the growing numbers of people with dementia. This is accounted for, in part, by the ageing population but there are other influences, including cardiovascular problems, lifestyle and environment. There is growing evidence that what we eat is one of the factors which affects our risk of dementia.

This chapter describes the evidence about diet and dementia and suggests strategies for achieving a brain-healthy diet.

What is healthy eating?

A healthy and varied diet should provide all the essential nutrients that your body and your brain need. It is important to eat a wide variety of foods to make sure you have an adequate intake of vitamins, minerals and fibre. A brain-healthy diet is one that reduces the risk of heart disease and diabetes, encourages good blood flow to the brain, and is low in fat and cholesterol.

What’s the evidence about healthy eating and dementia?

Most people are already aware that our diet, particularly our intake of saturated fats and salt, can affect our risk of heart disease and cause problems with blood circulation. The evidence is growing that the same factors also affect the risk of vascular dementia, where blood vessels may be damaged or arteries become blocked, causing the death of brain tissue.

Evidence also suggests there is a connection between cardiovascular disease and Alzheimer’s disease(20). This is strengthened by evidence that drugs used to treat cardiovascular disease also result in a lower incidence of Alzheimer’s disease(21) . The dietary risk factors for vascular dementia may therefore also be risk factors for Alzheimer’s disease and other forms of dementia.

The following sections consider key aspects of our diet that seem to make a difference.

Oily fish
The omega-3 oils found in oily fish like salmon, sardines, mackerel and herring can help prevent furring or hardening of the arteries and high blood pressure, which can raise dementia risk.

One American study(22) assessed the diet of 800 people aged over 65 by giving them a questionnaire about how often they ate various fish items. They found a 60% reduction in risk of Alzheimer’s disease in people who ate oily fish at least once a week compared with those who rarely or never ate fish. A later study(23) by some of the same research team looked at fish consumption and cognitive decline. Those who ate fish twice a week had a 13% lower rate of annual cognitive decline than those who rarely or never ate fish.

Another study in France looked at the risk of dementia from eating meat and fish, since fish is rich in polyunsaturated fatty acids while meat contains high levels of saturated fatty acids(24). The study found that elderly people who ate fish or seafood at least once a week had a 66% reduction in risk of developing dementia. There was no significant association between meat consumption and dementia risk. Other research has, however, suggested that meat eaters are at higher risk – see the following section (below) on Dietary fats.

The role of oily fish as part of a heart-healthy diet has received a lot of positive press coverage, although press reports of a study published in April 2006 cast some doubts. Researchers at the University of East Anglia reviewed 89 studies into the health effects of omega-3 fats for the risk of death, cardiovascular disease and cancer(25). They found that there was no clear evidence that omega-3 fats helped prevent various kinds of heart disease, including heart attacks, heart failure and angina. One of the studies they considered, of men with stable angina, found that those given high amounts of oily fish were at a higher risk of heart attack and a higher than expected number of deaths occurred (26).

The press played up this finding even though the researchers themselves said that the public should continue to follow UK guidelines about eating oily fish. Although one study found a worrying higher risk of heart attack or death, other large studies have suggested a benefit from consuming omega 3. The guidelines say that people should aim to eat two portions of fish a week, one of which should be an oily fish. The researchers did, however, suggest that the evidence should be reviewed regularly and that “It is probably not appropriate to recommend a high intake of omega 3 fats for people who have angina but have not had a myocardial infarction [heart attack]”.

Dietary fats
Fats can be described as saturated or unsaturated.

Saturated fats tend to be solid at room temperature, like lard, butter, block margarine, cheese and the fat you find on red meat or chicken. Whole milk also contains saturated fat.

Unsaturated fats tend to be liquid at room temperature and usually come from vegetable sources. They can be monounsaturated or polyunsaturated and are found in vegetable oils like sunflower, olive or soya as well as in oily fish, and some soft margarines.

There is another type of ‘bad’ fat called transunsaturated fats (or transfats). These are formed during the solidifying of vegetable oils through a process called hydrogenation, used by food manufacturers to extend the shelf life of food. Transfats tend to be found in processed foods which are often also high in salt and sugar like pies, biscuits and cakes.

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Why do dietary fats matter to the brain?

The Mental Health Foundation explains it well in its recent publication Feeding minds: the impact of food on mental health(27).

“The brain is partly composed of billions of nerve cells, known as neurons. Neurons use their unique physical structure to allow the brain to communicate within itself and throughout the rest of the nervous system. Each neuron is connected to thousands of other neurons by branches called axons and dendrites. Each neuron, axon and dendrite is predominantly composed of fat, or ‘lipid’ and these are derived from the diet. Specifically, they are made from highly unsaturated fats, which ensures that they are highly flexible and can work rapidly. Between each branch, there is a gap where messages (called neurotransmitters) are passed back and forth. These messages allow neurons to communicate information amongst themselves.”

“Because the brain is composed of about 60% fat (when water is removed), the fats we eat directly affect the structure and substance of the brain cell membranes. Saturated fats – those that are hard at room temperature, like lard – make the cell membranes in our brain and body tissue less flexible. If we eat large quantities of saturated fats, their rigidity is reflected in the rigidity of the brain cells.”*

“Although some fat is often considered unhealthy, it is vital for proper brain functioning. The ‘dry weight’ of the brain is composed of about 60% fat, including saturated fat and cholesterol, with approximately 20% of that made from the essential fatty acids, omega-3 and omega-6.”

Omega-3 and omega -6 are called essential fatty acids because they are necessary but can’t be made in the body – they have to be obtained from the food we eat.

* our emphasis

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Transfats and saturated fats are known to make brain cell membranes less flexible and fluid, affecting the ability of brain cells to communicate with one another. Having too much saturated fat can also increase the amount of cholesterol in our blood, which increases our chances of developing heart disease and strokes. So it makes sense to avoid these ‘bad’ fats as much as possible and to improve our intake of the ‘good’ monounsaturated and polyunsaturated fats and essential fatty acids.

Sources of good fats are oily fish (such as salmon, mackerel, herring and sardines) and soft polyunsaturated spreads as well as olives and olive oil, groundnut oil, sunflower oil, sesame oil, nuts and avocados.

Omega 6 fats are found in a variety of seeds, vegetables and vegetable oils. Omega-3 is not just found in oily fish. It is also found in green leafy vegetables, walnuts, soybeans, flax oil and omega-3 rich eggs.

A high intake of saturated fat seems to be a risk factor for Alzheimer’s disease as well as vascular dementia, with many studies showing a positive association between intake of saturated fat and incidence of Alzheimer’s disease, as well as a protective effect for polyunsaturated fats.

Reviewing the evidence on diet and Alzheimer’s disease, Morris (2004) describes three dietary studies which looked at fat consumption(28). In one study(29), 815 people in Chicago aged 65 or over were asked to complete a food frequency questionnaire. They were then assessed an average of 2.3 years later. The people with the highest consumption of saturated and transfats were 2.2 times more likely to have developed Alzheimer’s disease than the group who ate the least fat. Higher intake of monounsaturated and polyunsaturated fats were also associated with a lower risk of Alzheimer’s disease. Another study in New York (30) found a greater risk associated with total fat and saturated fat intake but no benefit from polyunsaturated fats. A Dutch study (31) found there was an increased risk from higher intakes of total fats and saturated fats after two years but not after six years follow-up.

American researchers are conducting various studies into people who have a genetic risk of Alzheimer’s disease because they have one or two copies of the ApoE ε4 gene. Because only about half of those go on to develop the disease, the scientists are trying to find out why some do and some don’t, and what factors might be involved. They found that people with the ApoE ε4 gene who ate a high-fat diet (where more than 40% of the diet consisted of fat) during their 40s and 50s are seven times more likely to develop Alzheimer's disease than people who don't have the gene(32). People in the same age group with the gene who ate a low-fat diet were four and a half times less likely to develop Alzheimer's disease than people without the gene.

The so-called ‘Mediterranean diet’ features high intakes of fruit and vegetables, bread, pasta, potatoes and red wine, together with olive oil, a monounsaturated fat, and small quantities of meat, fish and dairy products. Recently, researchers have looked at the potential of this way of eating to reduce dementia risk and cognitive decline(33)(34). These studies differ from others because they consider a complete diet rather than individual types of food. The most recent of these studies by Scarmeas and colleagues found that the people who had the highest intake of Mediterranean diet foods had a 40% lower risk of dementia than the people with the smallest intake.

Although more studies are needed, cutting down on saturated and total fat is likely to have other health benefits so there is no reason not to make suitable changes to what we eat. But remember, certain fats are essential to health, so we shouldn’t cut out fat completely.

Antioxidants/Vitamins C and E
Free radicals are a by-product that occurs when the body uses oxygen. They are harmful and can cause damage inside the cells of the body. Environmental factors such as pollution and cigarette smoke can increase the level of free radicals in the body. Antioxidants are the body’s defence system against free radicals, as they mop up these destructive molecules.

If antioxidants are unavailable, or if there are too many free radicals in the body, damage can occur. The danger from free radical damage increases with age. Some researchers think that the destructive effect of free radicals may be one of the causes of brain cell death in Alzheimer’s disease. This has led to interest in whether increasing antioxidant intake through diet or vitamin supplements could provide any protection against Alzheimer’s disease.

Findings from research projects do not all reach the same conclusion on whether eating more antioxidants may prevent or delay the development of Alzheimer’s disease.

One six year study concluded that high dietary intake of Vitamins C and E may lower the risk of Alzheimer’s disease(35). They found that those who had the highest intake of Vitamin E had a 43% lower risk of developing Alzheimer’s disease compared with the people who had the lowest intake. There was a slight association between high intake of Vitamin C and risk of Alzheimer’s disease(36).

However, a further study found that neither dietary intake nor taking supplements of vitamin C and E were associated with a decreased risk of Alzheimer’s disease.
In the Chicago Health and Aging project, 815 people assessed as not having Alzheimer’s disease were followed for four years. Those with the highest intake of vitamin E from food, but not from vitamin supplements, had a 70% lower risk of developing Alzheimer’s disease(37). This reduced risk was only found in those people who did not have the ApoE ε4 gene. Vitamin C did not seem to offer any protection.

It is not yet known whether increasing antioxidant levels through diet could prevent or slow the progress of Alzheimer’s disease. However, a balanced diet that includes at least five portions a day of fruit and vegetables is good for general health and may provide some protection for the brain.

Fruit and vegetables are a good source of natural antioxidants; berries, walnuts, sunflower seeds, pomegranate and ginger are particularly good but any fruit or vegetables should be good for you, depending on how you prepare and eat them. Cooking vegetables in saturated fats or heavily salted water then serving them with butter would cancel out a lot of the benefits; cooking or serving fruit with lots of sugar would do the same.

Vitamin C is found in citrus fruits, berries, tomatoes, and various vegetables. Vitamin E is found particularly in foods like vegetable oils, nuts (especially almonds) and seeds (especially sunflower seeds). Smaller amounts are found in whole grains, fruits, leafy green vegetables and egg yolks.

Vitamin supplements should not be necessary in a balanced diet although some people may benefit. If you are thinking about taking vitamin supplements, you should check with your GP to make sure they are safe to take with any other pills you already take and you should not consume more than the recommended daily allowance of any supplement. Some vitamins may be dangerous if taken in large quantities.

Folate (Folic Acid) and Vitamin B12
Homocysteine is an amino acid (a building block for proteins) in the blood. Too much of it can damage blood vessels and it has also been linked with dementia.(38) Folate and other B vitamins, including Vitamins B6 and B12 help process and lower levels of homocysteine. Folic acid is the manufactured version of folate.

Fortified cereals, green leafy vegetables, orange juice, yeast extract and liver are all good sources of folate.

There is evidence that having too little folate may contribute to the cognitive impairment of some older people’s brains. This may result in reversible damage or possibly increase the risk of Alzheimer’s disease and vascular dementia(39).

One study found a 55%(40) reduced risk of Alzheimer’s disease in people eating above the UK recommended daily allowance of folate (200 micrograms). In a Swedish study of 370 healthy older people who were followed for three years, those who had low B12 and folate levels at the beginning of the study were twice as likely to have developed Alzheimer’s disease by the end of the study(41). In the Framingham study in the United States, scientists measured the homocysteine levels of 1,092 people who did not have dementia. After following them up for an average of eight years, they found that the people with raised higher homocysteine levels had double the risk of developing Alzheimer’s disease(42).

Closer to home, the OPTIMA (Oxford Project to Investigate Memory and Ageing) project found that people with the highest levels of homocysteine in their blood were 4.5 times more likely to develop Alzheimer’s disease than others. They also found that people with low levels of Vitamin B12 and folate were four and three times more likely to develop Alzheimer’s disease(43).

Does this mean that high levels of homocysteine actually cause dementia? At the moment, researchers simply do not know. While many studies have shown that levels of folic acid and vitamin B12 are reduced in dementia and others have demonstrated high levels of homocysteine in Alzheimer’s disease, the high levels of homocysteine found could be a result of Alzheimer’s disease rather a cause.

It is not yet known whether increasing your intake of folate either through diet or by taking supplements will reduce the risk of developing dementia. More research is necessary to fully understand what benefits folate may have in protecting the brain(44).

Anyone thinking of taking folic acid or Vitamin B12 supplements should check with their doctor first. There is some evidence that, very rarely, taking folic acid when the level of vitamin B12 is very low can cause nerve cell damage. It has also been suggested that folic interferes with some epilepsy drugs.

Salt
Vascular dementia is caused by problems with the supply of blood to, or within, the brain. Research into vascular dementia has shown a strong association between diet and brain function. High blood pressure, which is linked to high salt intake, is known to increase the likelihood of vascular dementia(45).

To make matters worse, some research suggests that older adults prescribed drugs to lower blood pressure and whose blood pressure stays low are also at increased risk of dementia(46). Whether this is because their brains are not getting enough blood or oxygen because their blood pressure is low, or whether their low blood pressure reflects changes due to developing dementia is not clear. Either way, it makes sense to try to keep your blood pressure within the normal range, without having to take drugs.

As the Food Standards Agency Scotland points out it is actually the sodium in salt that can lead to health problems (47) – and most of the sodium in our diet comes from salt. We should have no more than 6g salt a day, which is about a teaspoonful.

See below for more on recommended salt/sodium levels and how to cut down.

Cholesterol
Cholesterol is a fatty substance which is essential to healthy life. It is mostly produced in the liver, but is also provided from the food we eat(48).

When the cholesterol level in our blood is high, it helps cause a fatty build up in the lining of the blood vessels. High cholesterol levels can cause narrowing of the arteries (atherosclerosis), heart disease, heart attacks, and strokes. If you also have high blood pressure and/or smoke, this increases your risk of these health problems even more.

While the link between high levels of cholesterol and risk of vascular dementia seems clear(49), as Chapter 3 has already indicated, there is also research linking high levels of cholesterol with increased risk of Alzheimer’s disease(50)(51).

The Stroke Association (see section Other sources of information and advice) recommends that men over 35 and women over 45 should have their cholesterol checked. You may already have your cholesterol level checked routinely if you have a family history of heart disease or high cholesterol, high blood pressure, evidence of heart disease, or diabetes.

There are two types of cholesterol – LDL (low density lipoproteins) and HDL (high density lipoproteins) – which perform different function. LDLs carry cholesterol from the liver to the cells while HDLs carry any cholesterol that isn’t needed from the cells back to the liver, from where it can be excreted. When the liver makes too much cholesterol, LDL cholesterol is deposited in the walls of the blood vessels in a similar way to your kettle getting furred with limescale. That is why LDL cholesterol is described as ‘bad’. HDL cholesterol is called ‘good’ because it helps remove cholesterol from the arteries.

A number of studies have explored the role of drugs called statins, used to lower LDL cholesterol, in reducing the risk of dementia. As Chapter 8 demonstrates, it is still not clear whether statins reduce dementia risk or not. Eating a healthy diet and being more physically active are things you can do to help reduce your cholesterol level without necessarily taking drugs, unless your doctor says you need to.

Obesity/Healthy weight
Linked to healthy eating, and exercise (see Chapter 5) is a person’s weight. Obesity triples the risk of dementia, women warned was the headline in the Scotsman on 29 April 2005. This article reported on a Californian study which tried to measure any association between obesity in middle age (measured by body mass index and skinfold thickness) and risk of dementia in later life (52). What was particularly important about this study was the number of subjects involved (more than 10,000) and the length of the study (27 years).

The subjects were assessed between 1964 and 1973 when they were aged 40-45. They were then assessed again between 1994 and 2003 to determine how many had developed dementia. People who had been obese in middle age had a 74% increased risk of dementia while overweight people had a 35% greater risk compared with those of a normal weight.

Obese women fared worse than obese men, having a 200% increased risk compared with women of normal weight. This may be partly explained by there being more obese women than men in the study, but it may also have something to do with differences between the sexes in how body fat is distributed and the effect that has on risk of heart disease and diabetes, both risk factors for dementia.

The researchers suggest further studies that could be useful in explaining the link between obesity and risk of dementia. One theory is that fat cells produce proteins called cytokines which make blood cells liable to inflammation. Any inflammation in the brain could lead to the loss of nerve cells, leading to dementia.

Other research, this time with older subjects, has also found a possible association between being overweight and the risk of Alzheimer’s disease. Swedish researchers found that, for every 1.0 increase in body mass index in women aged over 70, the risk of Alzheimer’s disease increase by 36%(53).

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Body Mass Index

Body mass index (BMI) gives a measure of your weight relative to your height. You can calculate your BMI by taking your height in metres and multiply that figure by itself. Then measure your weight in kilograms. Divide your weight by your height squared to give your BMI.

If your BMI is between 25.0 - 29.9 you are classed as overweight; between 30 and 39.9 you are classed as obese.

What the BMI can’t do is calculate the percentage of body fat a person has, so you may need to make some adjustments for your age, build and gender. But the BMI can indicate that you may need to take steps to bring your weight down for the sake of your health.

There are many BMI calculators available on the Internet which can calculate your BMI using metric or imperial measures. Try visiting www.healthyliving.gov.uk

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Does healthy eating reduce the risk of dementia?

The simple answer is that we don’t really know for sure. The evidence is stronger for vascular dementia where a healthy diet can help reduce the risk of high blood pressure, heart disease, high cholesterol and diabetes, all risk factors for vascular dementia.

The evidence is less clear-cut for Alzheimer’s disease, although it points the same way. More research is needed, although it would be difficult and expensive to conduct a trial using sufficiently large numbers of people, over a long-enough period of time to reach very firm conclusions.

However, even if we can’t say for certain that what you eat or don’t eat will affect your risk of dementia, or if eating or avoiding any particular type of food makes the most difference, eating more healthily will benefit your health generally and, as well as giving you the best chance of reducing your dementia risk, may also help to reduce your risk of a variety of diseases, including diabetes, heart disease and some cancers.

How to eat more healthily

Eating a more healthy diet is likely to mean making small changes to what you already do, eating less of some things and more of others. Most of us already know the main messages – eat more fruit and vegetables, more bread and cereals, less fat, less salt and so on. We can all improve on what we eat, without completely stopping eating what we’ve always eaten or spending more on food.

Aim to eat five or more portions of fruit and vegetables a day. Some people may find it harder than others to get access to fresh fruit and vegetables but tinned (although not in syrup or with too much salt), frozen and dried fruit and vegetables can all contribute too. Note that dried fruits contain a lot of natural sugar, so only a single, matchbox sized portion should be eaten daily. A portion of fruit is a whole apple, banana or orange, or two smaller fruits like plums or satsumas; a portion of vegetables would be 2 tablespoonsful.

Eat more starchy foods like bread, breakfast cereals, rice, pasta and potatoes – wholegrain, wholemeal or brown varieties where possible. Potatoes do not count as any of your daily portions of fruit and vegetables.

Eat more fish – at least two portions a week. One portion should be oily fish like salmon, mackerel and sardines - fresh, tinned or frozen. Tinned tuna, however, does not contain the beneficial types of oil and so does not count as a portion of oily fish.

Cut down on salt – no more than 6g a day (one teaspoonful). It is actually the sodium in salt that is harmful. When checking food labels – 0.5g sodium per 100g is a lot, 0.1g per 100g is a little. Avoid automatically adding salt to cooking and at the table.

Avoid cakes, biscuits, fizzy drinks and sweets – this will help control your intake of fat and sugar.

Reduce the amount of saturated fat that you eat like butter, lard, cream, whole milk and palm oil. Polyunsaturated fats such as corn oil and sunflower oil can help lower your LDL (or bad) cholesterol but too much can lower the protective HDL cholesterol. Monounsaturated fats like olive oil and rapeseed oil can help lower LDL cholesterol but have no effect on HDL. When reading the labels on processed or packaged foods, fat may be listed as fat content and/or saturated fat content. 5g per 100g is a low fat content; 20g per 100g is a high fat content; 1g is a low saturated fat content; 5g is a high saturated fat content.

Dairy products should be eaten in moderation and in low-fat types where possible – low fat spreads, skimmed or semi-skimmed milk, low-fat yoghurt and small quantities of cheese (30g or 1 ounce a day).

Drink alcohol in moderation. The recommended maximum weekly alcohol limits are 21 units for a man and 14 units for a woman. See Chapter 8 for the evidence on alcohol and dementia.

The British Heart Foundation has a useful guide to portion sizes for a variety of foods in its publication So you want to lose weight … for good (see section Other sources of information and advice).

Cooking methods

As well as changing the types of food you eat, it is important to consider how you cook them. Steaming vegetables retains more nutrients; stir-frying in a suitable oil can make a variety of vegetables look and taste more interesting and is quick to do. Boiling should be done with no or very little salt. Roasting vegetables in a little olive oil takes longer but a variety of vegetables can be cooked in this way. Adding herbs or spices can add flavour instead of using salt.

Social benefits

It’s not just what you eat that matters. If you live on your own, cooking and eating well may not seem to be worthwhile, although it is still very important to health. Sharing meals with family and friends can provide social stimulation as well as an incentive to eat well. (see Chapter 7)

See www.healthyliving.gov.uk or phone 0845 2 78 88 78 for more help with healthy eating.

Next section: Physical activity and the brain
References
Glossary
Return to risk reduction contents page

Useful links:

Information about dementia
The OPTIMA project
The Stroke Association
Online BMI(Body Mass Index) calculator at Healthy Living
The British Heart Foundation