Moderately high levels of the amino acid homocysteine may substantially increase the risk of stroke and AlzheimerÃÂs disease as well as a non-Alzheimer's form of dementia, researchers from Queen's University of Belfast in Northern Ireland report.
The results of the new study do not prove that homocysteine is directly responsible for increasing these risks, but the evidence is strong enough to encourage people to take in more vitamins that can lower homocysteine levels, such as folic acid, B6 and B12.
Prior research has shown that elevated levels of homocysteine may increase the risk of heart disease and stroke by damaging artery walls. Diet has a major effect on homocysteine levels. Folic acid and other B vitamins may lower homocysteine by breaking down the amino acid. The benefits of lowering homocysteine levels have not been proven, however.
This study measured homocysteine levels in 64 individuals who had had a stroke, 83 people with Alzheimer's and 78 people with vascular dementia, a form of dementia caused by diminished blood flow to the brain. They also studied a "control" group of 71 healthy elderly people. Since there is no consensus on how much homocysteine is too much, the researchers classified high homocysteine levels based on the quarter of healthy people who had the highest levels.
Compared to the healthy elderly, people who had had a stroke were more than five times as likely to have elevated homocysteine. The odds were increased nearly three times in people with Alzheimer's and almost five times in those with vascular dementia.
What is now needed, say the scientists, are clinical trials that investigate whether vitamin B and folate supplementation can reduce the risk of stroke or dementia. The researchers state that because dietary habits are so different among people, it may be appropriate to recommend a higher dose, such as 2 to 5 milligrams folic acid and a similar dose of vitamin B12 daily.
Since the late 1990s, the US and Canada has required that certain grain foods, including bread, cereals, flour and pasta, be fortified with folic acid, but according to some experts there is a case for further supplementation even when normal foods are fortified.
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