Cholesterol and dementia risk explained

Having high levels of bad cholesterol in our 40s and 50s is associated with an increased risk of dementia.

Low levels of good cholesterol in our 30s to 60s can also increase our risk of dementia.

The diagram below illustrates how levels of good and bad cholesterol can affect our dementia risk.

Lots of different factors can contribute to high cholesterol. These include:

• eating too much fatty food
• not doing enough physical activity
• being overweight
• smoking
• drinking alcohol.

High cholesterol can also run in families. So, we may be more likely to have it if a close relative does too.

High cholesterol does not usually cause symptoms. Many people don’t know they have it.

It’s a good idea to have your cholesterol checked regularly from midlife. This can be done with a simple blood test at a GP surgery or some pharmacies.

If you are told you have high cholesterol, there are medications and lifestyle changes that can help manage it.

High cholesterol is linked to an increased risk of dementia, particularly vascular dementia. The link with Alzheimer’s disease is more complex and less direct.

Damage to blood vessels in the brain

Over time, cholesterol, especially bad cholesterol, can build up in the walls of blood vessels. This can make them stiffer or narrower – known as atherosclerosis.

If this happens in the brain:

• less blood can reach brain cells.
• brain cells may not receive enough oxygen and nutrients to work properly.
• small areas of damage can build up over time.

This kind of damage is a major cause of vascular dementia.

Increased risk of stroke and small vessel disease

High cholesterol increases the risk of stroke. A stroke damages the brain and in turn increases dementia risk.

Even small or “silent” strokes can affect memory and thinking especially if they happen more than once.

Damage to small blood vessels deep in the brain can also build up over time. This is called small vessel disease, which is another cause of vascular dementia.

Often linked with other dementia risk factors

High cholesterol often occurs alongside other conditions that affect brain health, including:

• high blood pressure
• type two diabetes
• being overweight.

Because these conditions often develop together, it can be difficult to separate the effect of cholesterol on its own.

Possible links with Alzheimer’s disease

Some studies suggest cholesterol may be involved in changes in the brain linked to Alzheimer’s disease.

However, the evidence is mixed.  High cholesterol has not been shown to directly cause Alzheimer’s disease. The strongest evidence links cholesterol to blood vessel damage which can be a contributing factor in the development of Alzheimer’s, rather than directly causing Alzheimer’s itself.

Hearing loss is one of the biggest risk factors for dementia we may be able to influence.

For every 100 cases of dementia worldwide, almost half (45%) could be prevented or delayed. Seven of those 45 cases are linked to unmanaged high cholesterol in midlife.

So, if everybody could effectively manage their cholesterol levels, there'd be seven fewer cases of dementia for every 100 people who develop it now.

Find out more: Addressing 14 health and lifestyle factors could prevent nearly half of global dementia cases - Alzheimer's Research UK

Statins are a medicine that can help lower bad cholesterol.

Some research suggests that taking statins over a long time may reduce the effect that high cholesterol has on dementia risk. However, there is not enough evidence yet to say statins can prevent dementia.

A question we are asked frequently is if statin use leads to dementia. There is no evidence that statins increase the risk of, or cause, dementia.

Managing high cholesterol via medications and lifestyle changes is important. It helps reduce the risk of heart disease and protects blood vessels in our brains. Better heart health is linked to lower dementia risk.

Find out more about cholesterol, statins and dementia risk.

There is no strong evidence that low cholesterol causes dementia.

Some people worry that lowering cholesterol, including by taking statins, might be bad for the brain. But there is no strong evidence to support this.

The brain needs cholesterol, but it makes its own. It does not rely on cholesterol from the blood. Lowering cholesterol in the blood does not mean the brain is “starved” of cholesterol.

Overall, high levels of bad cholesterol are more clearly linked to dementia risk than low cholesterol, particularly in midlife.

Managing high cholesterol is important for heart health, which also helps protect the brain.

Most of what we know about dementia risk comes from observational studies, which follow groups of people over time to look for patterns in health and lifestyle.

For example, studies like Insight 46 have followed people for decades to understand how health across life is linked to brain health and later on.

This is often the most practical way to study dementia risk. Many risk factors cannot be tested in trials in a fair or ethical way. Dementia also develops over many years, so studies can take a long time to show results.

Observational studies can show when something like our diet or occupation are linked to a higher or lower chance of dementia. But they cannot prove that something directly causes dementia, or that changing it will definitely reduce risk. These studies look at patterns across large groups, not what will happen to any one person.

Randomised controlled trials give stronger evidence because participants are assigned to different groups at random. This design makes it more likely that differences in outcomes, for example our risk of dementia, are caused by the intervention, for example a diet change, rather than by other factors.

But these studies are harder to do in dementia research. They often take many years and may test several changes at once, making results harder to interpret.

Newer trials are helping to build a clearer picture of what may support brain health. No single study can give a definite answer, but it is all research findings together that help us understand what is important for our brain health and risk of dementia.