Cholesterol plays a vital role in the body – it’s an essential component of cell membranes and is necessary for the production of vitamin D and other hormones – but too much of it can be a problem. Elevated cholesterol levels in the bloodstream are linked to heart disease, and there is some evidence that high cholesterol may be associated with an increased risk of dementia as well. Before you sign up for a regimen of cholesterol-lowering drugs, however, it’s important to consider what we know about cholesterol as well as what we know about Alzheimer’s disease and other forms of dementia.
Serum cholesterol is primarily produced in the liver and carried by low-density lipoproteins (LDLs) to all the places in the body where it’s needed. LDL is the “bad” cholesterol that forms plaque in your arteries and creates the risk for heart attacks. High-density lipoproteins (HDLs) carry it back to the liver for disposition – that’s the “good” form of cholesterol. Total blood cholesterol under 200 mg/dL is considered optimal, with no more than 100 of that being LDL. Cholesterol levels between 200 and 239 are considered borderline high and 240 or over is the danger zone, with a risk of heart disease that’s double what it is for those whose total cholesterol is in the optimal range. That’s why so much of the conversation about cholesterol has focused on its role in heart health.
At any given time, however, as much as 25 percent of the cholesterol in your body is in your brain, where its role is to help build the myelin sheaths that protect neurons and assist in brain development and signaling. The brain both produces and metabolizes cholesterol, and dysfunction in those processes have been linked to several neurological disorders, including dementia.
The most common form of dementia is Alzheimer’s disease, which is characterized by the presence of beta-amyloid and neurofibrillary tangles in the brain. Research has implicated ApoE4, a protein that transports cholesterol in the central nervous system, in the development of the disease. Vascular dementia, the second most common form, is associated with cerebrovascular disease and often occurs after a stroke, which may be triggered by plaque buildup in blood vessels. Associations are not hard evidence, however, although they are cause for concern and further study.
When epidemiologists have looked at large trends, they have seen that middle-aged individuals who are obese or who have type 2 diabetes or heart disease, as well as high cholesterol, are more likely to develop dementia in their old age than those who don’t have those earlier risk factors. We know that the brain changes that are characteristic of Alzheimer’s disease and other dementias start many years before signs of cognitive decline emerge, so addressing health issues in middle age may be an opportunity to reduce later risk. That includes, but is not limited to, managing your cholesterol levels.
To reduce those levels, the first step is to modify any lifestyle factors that may have raised them. Lose weight if you’re overweight, substitute whole soy protein for animal protein, reduce the amount of sugar and flour in your diet, increase your activity, and manage your stress levels. If lifestyle changes don’t adequately reduce your risk for heart disease, you may want to consider statins – but know that statins have side effects that some people find intolerable. Although statins do lower cholesterol, their benefits in reducing the risk of dementia have not been established. For more, see my guide to cholesterol.
Andrew Weil, M.D.
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