Harvard Health Letter

Ask the doctor: Can B vitamins help prevent dementia?

Q. Is it true that B vitamins can reduce my risk of Alzheimer's disease and other types of dementia?

A. The simple answer appears to be "probably not." But few things in medicine are simple. A century ago, we ate a lot more foods rich in B vitamins than we eat today. Diets low in B vitamins—particularly folic acid, vitamin B6, and vitamin B12—can raise blood levels of a natural chemical called homocysteine. This, in turn, can promote atherosclerosis of the arteries of the heart and brain—resulting in heart attacks, strokes, and dementia.

However, since the 1980s, many foods have been supplemented with B vitamins. As a result, substantially fewer people have high homocysteine levels. Therefore, for most people there is not much evidence that B vitamin supplements protect against heart disease or various types of dementia. There are a small number of people who are born with genetic defects that cause high homocysteine levels. B vitamin supplements can dramatically lower homocysteine levels in these unusual people, and that probably offers protection against dementia.?

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