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Can having high cholesterol reduce your chances of dementia?

People over the age of 85 with high levels of cholesterol have a reduced risk of marked cognitive decline, according to a new study. Does this mean that having high cholesterol in old age can prevent the onset of dementia?

Cholesterol is a waxy substance produced by the liver which is also found in many foods. It circulates through your bloodstream in carriers made of fats and proteins, known as lipoproteins.

These lipoproteins are classified according to their density. Low-density lipoprotein (LDL) cholesterol is often called “bad” cholesterol, as it contributes to fatty buildup in arteries. High-density lipoprotein (HDL) cholesterol is often referred to as “good” cholesterol as it carries cholesterol away from the arteries and back to the liver. Collectively, the different forms are referred to as total cholesterol.

There’s no one cholesterol type. Shidlovski/Shutterstock

Cholesterol is essential for normal function of cells throughout the human body, but has gained a bad reputation as it is also linked to coronary heart disease. This link means that cholesterol-lowering drugs, like statins, are used to manage the risk of having a cardiovascular event, such as a heart attack or stroke. Nevertheless, scientific opinion over cholesterol and the use of statins to reduce cholesterol levels is split, making it an intriguing and controversial area.

Interestingly, research has shown that cholesterol is involved in a loss of cognitive function. Cognitive function includes mental processes such as attention, processing speed, learning and memory and verbal fluency. Dementia, including Alzheimer’s disease, occurs when these functions decrease significantly more than you would expect with normal ageing.

While the studies in this field lack consistency, there is evidence that high cholesterol in middle age increases the risk of developing Alzheimer’s disease. Also, alipoprotein E, a protein that acts as a cholesterol carrier in the brain, is a major risk factor for the development of late-onset Alzheimer’s.

What the new study found

The new study compared cognitive function in people of different ages. The research team looked at existing data from the Framingham Heart Study, an ongoing cardiovascular study of residents of Framingham, Massachusetts.

The researchers evaluated a variety of total cholesterol values, including “midlife” total cholesterol, “late-life” total cholesterol, mean total cholesterol since midlife, and change in cholesterol since midlife. Midlife would be around 40 years of age, and late-life around 75 years of age.

The team assessed whether marked cognitive decline was associated with any of the cholesterol values measured. They also studied whether these associations changed depending on the age when cognitive assessment was done.

The study showed that several cholesterol values, including increased cholesterol levels since midlife, were associated with increased risk of a marked cognitive decline. However, as the age of the people studied increased, some of these associations were reduced or reversed.

Most interestingly, in subjects aged 85 to 94, a high midlife total cholesterol level was associated with a reduced risk for marked cognitive decline. This finding is in contrast with both younger age groups in this study, and other studies where midlife cholesterol was associated with increased risk of cognitive decline.

The take home

What does this new finding actually mean in real terms then? It is unlikely that high total cholesterol per se is actually good for cognitive function at 85 years of age. This means that it’s probably not wise to attempt to increase your cholesterol or to stop taking any medication that reduces cholesterol.

Controlling cholesterol levels, especially at midlife, would probably still benefit most of us. Taking into account the findings of other studies, it is almost certain that the people in this study, aged 85 and older, had unknown additional protective factors that prevented them from undergoing marked cognitive decline. This means that the risks associated with high cholesterol do not apply to them.

Until these factors have been identified it is impossible to know if cholesterol is a marker of these additional factors, or if cholesterol itself is important. For now cholesterol remains an intriguing and controversial subject.

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