What does high cholesterol do to your brain as you age?

High cholesterol in middle age is associated with a greater risk of dementia and cognitive decline in later life. This association has been found in multiple observational studies, but it is an association, not a proven cause-and-effect relationship. High cholesterol falls into the same risk category as high blood pressure and diabetes when it comes to vascular damage to the brain.

Interestingly, when measurements are taken only at an advanced age, that association disappears, or even reverses. In people aged 65 and older, higher cholesterol levels sometimes go hand in hand with better cognition. This may seem contradictory, but it is possibly related to selection: those who survive to old age with high cholesterol and no damage are a different group from those who do not.

What does present a clear risk in older adults is large fluctuations in cholesterol from year to year. Older adults with the greatest swings in total cholesterol had a 60% higher chance of developing dementia than those with stable values; for LDL (the 'bad' cholesterol) that figure was 48% higher. High variability was also associated with faster decline in memory and processing speed. No comparable association was found for fluctuations in HDL or triglycerides.

Then comes the logical question: do cholesterol-lowering drugs (statins) help the brain? In observational studies the picture looks promising, but in controlled experiments in which people were randomly assigned to statins or a placebo, no demonstrable benefit for cognition was found. Statins therefore do not demonstrably protect the brain in old age.

Cholesterol is, incidentally, not purely an enemy of the brain. It is a building block for the connections between brain cells, and levels that are too low can also be harmful. At the same time, cholesterol in cell membranes contributes to the production of amyloid-beta, the plaques associated with Alzheimer's disease. The balance is therefore complex, and there are as yet no firm recommendations for a specific cholesterol target purely for brain health.