What are the risk factors for dementia?

Several key risk factors for dementia have been identified:

• Ageing
• Genetics
• Gender
• Medical history, particularly cardiovascular problems
• Lifestyle and environment.

Of these factors, age, genetics and gender (what we are) cannot be controlled or modified while medical history, lifestyle and environment (what we do) have the potential to be modified.

Ageing

Dementia may occur at any age, although rarely below the age of 60. It becomes more common with increasing age, affecting one person in 20 aged over 65; one in five over 80; and one in three over 90.

Ageing has been consistently shown to be the major risk factor for Alzheimer’s disease and other dementias(4)(5).

Although age is the most significant risk factor that we know about, dementia is not an inevitable part of ageing. There are other risk factors that increase or reduce our likelihood of developing dementia. These might be environmental, genetic or lifestyle factors.

Genetics

The term ‘dementia’ covers the effects of a range of diseases. Many of these are likely to have a genetic basis, but for most forms of dementia this is not a straightforward single gene.

Most of the research on the genetics of dementia is about Alzheimer's disease. There are rare types of Alzheimer’s disease where there is a family link caused by a single defective gene. This is called familial Alzheimer’s disease and usually affects people under the age of 65. So far, three different genes of this kind have been identified. Only a very few families are affected by each gene and most cases of early onset Alzheimer’s disease are not inherited in this way. On average, half of the children of someone with one of these rare genetic defects will inherit the disease.

In most cases of Alzheimer's disease, the role of genetics is less clear. While particular genes do not cause the disease, they may affect the risk of developing it. However, someone with a parent or other close relative with dementia has only a slightly increased risk of developing dementia, relative to the general population.

A gene called apolipoprotein E (ApoE) has been shown to play a part in Alzheimer’s disease and possibly vascular dementia, although more research is needed before a link can be proven for vascular dementia. The ApoE gene codes for a protein involved in carrying cholesterol in the blood. There are three types of ApoE: ApoE ε2, ApoE ε3 and ApoE ε4. Having one copy of the ApoE ε4 gene increases a person’s risk of developing Alzheimer’s disease by up to four times. Someone with two copies of ApoE ε4, one from each parent, has a 10 times greater risk; but only about 2% of the population have two copies of ε4.

The most common form of the gene is ε3. About 60% of the population have two copies of ApoE ε3 and are at average risk, which means that about half will develop the disease by their late 80s.

About one in six people have at least one copy of ApoE ε2. This form of the gene seems to have a protective effect, and people with it have a lower risk of getting Alzheimer's disease. The lowest risk is for people who have two copies of ApoE ε2.

It is important to recognise that this gene affects risk and is not a predictor of whether someone will develop Alzheimer's disease. Although ApoE ε4 increases the risk of developing the disease it does not make it certain. Many people who develop Alzheimer’s disease do not have an ApoE ε4 gene, and some with the ε4 type do not develop the disease. For this reason, there is no point in testing people to see which kind of ApoE they have.

While more research needs to be done to determine the relationship between the ApoE gene and vascular dementia, it is known that there are other genes which contribute to a person’s risk of developing other conditions which are linked to vascular dementia, such as diabetes, high blood pressure and high cholesterol.

Gender

Women may be slightly more likely to develop Alzheimer’s disease than men; it is not clear whether this difference is due to biology, to the fact that women tend to live longer or to their behaviour(6)(7).

Vascular dementia is more common in men than women across all age groups . This may be because risk factors for vascular dementia, such as high blood pressure and heart disease, are more common in men.

Overall, 66% of people with dementia are female. However, the proportion varies with age group: women account for only 37% of people with dementia between 65 and 69, but 79% of people with dementia aged 90 and above(9).

Medical problems

Conditions that affect the heart and blood circulation are particularly important for the risk of developing vascular dementia. High blood pressure, high cholesterol levels, diabetes, heart attacks, strokes and mini-strokes can all affect blood supply to the brain, leading to possible damage. Obesity in mid-life may also increase the risk of developing dementia(10) (11).

There is mounting evidence that risk factors for one type of dementia may also relate to other dementias. For example, having high blood pressure in middle age is a risk factor for both vascular dementia and Alzheimer’s disease, so lifestyle changes and/or medical treatment to lower blood pressure may help to prevent both these kinds of dementia, as well as mixed dementia where someone has both types.

Many people are already aware that their lifestyle – for example diet and exercise – can affect their risk of heart disease. The evidence is growing that the same factors also affect dementia risk. So there is even more reason to take steps now to improve your lifestyle; it may benefit both your heart and your brain.

High blood pressure

Several studies have shown that people with high blood pressure in middle age run an increased risk of dementia later in life. According to the Blood Pressure Association (12), a blood pressure reading that is consistently more than 140/90 mmHg is high. The top number, the systolic pressure, shows the pressure in your arteries when your heart is forcing blood through them. The bottom number, the diastolic pressure, shows the pressure in your arteries when your heart relaxes.

One study in Finland set out to investigate the relationship between raised blood pressure and cholesterol in middle age and Alzheimer’s disease in later life. The researchers chose a group of 1,449 people who had been involved in previous surveys since the 1970s and who were now aged 65-79. They found that those who had raised systolic blood pressure ( ≥160 mmHg) at the start of the study now have 2.3 times the risk of developing Alzheimer’s disease(13).

Treatment of high blood pressure in old age has been shown in several studies to reduce the risk of cognitive decline and dementia. In one 4 year randomised controlled trial, treating high blood pressure reduced the risk of dementia by 55%(14). Another study looked at people with a high risk of stroke and found that those given a blood pressure lowering drug had a 41% less risk of cognitive impairment in the next 2 years(15).

In a randomised controlled trial looking at about 6,000 people with previous strokes or ‘mini strokes’ (transient ischaemic attacks or TIAs), the researchers gave participants either a drug to lower blood pressure or a fake treatment (16). They found that those who had the treatment and had another stroke had a reduced risk of cognitive impairment or dementia. This suggests that reducing the impact of brain damage from strokes could reduce the risk of dementia in the future.

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 a person eats. When the cholesterol level in the blood is high, it contributes to a fatty build up in the lining of the blood vessels which increases the risk of narrowing of the arteries (atherosclerosis), heart attacks, and strokes. The risk of coronary heart disease also rises as blood cholesterol levels increase.

High levels of cholesterol have been linked in a number of studies(17)(18) with increased risk of Alzheimer's disease. Some research has suggested that people taking drugs called statins to lower their cholesterol levels have a lower risk of developing Alzheimer's disease, but the evidence on this is far from conclusive and considerably more research is needed before any firm conclusions can be made(19). See Chapter 8 for more information on statins and dementia.

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Go for regular health checks

What’s good for the heart seems to be good for the brain.

The Stroke Association recommends that men over 35 and women over 45 should have their cholesterol checked. You may ask to have it checked periodically after that, but your GP may do the test more frequently if you are in a high risk category - for example, if you have a family history of heart disease or high cholesterol, high blood pressure, evidence of heart disease, or diabetes. The Blood Pressure Association advises that a normally healthy person should have their BP checked first from the age of 20. If it is normal, then it should be checked every five years, more regularly if it is ever found to be abnormal.

Early prevention could help reduce your risk of dementia later in life.

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Lifestyle and environment

Other influences which research has identified include poor diet, lack of exercise, lack of social stimulation, and lack of intellectual stimulation. More will be said about these influences in later chapters. The final chapter will look at factors for which there is less conclusive evidence but which have received considerable media coverage. This includes aluminium, hormone replacement therapy, statins, anti-inflammatory drugs, alcohol and tobacco use, and vitamin supplements.

You cannot stop getting older, nor can you (generally) change gender or your genetic make-up. But you can take steps to improve your physical and mental health now to try to decrease the risk of developing dementia in 20 or more years’ time.

But can we truly prevent or delay dementia, and what can we do to reduce the risk of developing dementia?

There is no single thing that should be done but an individual is most likely to see the benefit of :

• eating healthily
• taking moderate exercise
• keeping up social networks
• exercising the brain.

Unfortunately there are no guarantees. We are all at some risk of developing dementia, some of us more than others. But even if an individual has some, or even all, of the risk factors he or she will not necessarily develop dementia.

Some people may wonder why they should bother. If someone can do all the right things but could still develop dementia, where’s the incentive?

Avoiding risk factors does not guarantee that you will avoid dementia, but it makes it more likely. A healthier lifestyle will have the added benefit of improving your health and wellbeing generally. Reducing the risk of dementia is one more good reason for keeping your heart healthy, maintaining a healthy weight, undertaking regular physical activity, staying involved in social activity and stimulating your brain - it should not only make you feel better now, but it may also help reduce your risk of developing other conditions such as heart disease, diabetes, strokes or depression.

This booklet does not suggest any weird or wonderful ways to avoid dementia. It looks at the evidence behind the newspaper headlines about preventing dementia and suggests some simple lifestyle changes that you can try to make now which will have positive benefits today and could make all the difference for your future.

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