homocysteine / vitamin B / folate
NEW YORK (Reuters Health) - Moderately high levels of the amino acid homocysteine may substantially increase the risk of stroke and Alzheimer's disease as well as a non-Alzheimer's form of dementia, researchers 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, according to the study's lead author, Dr. Stephen P. McIlroy of the Queen's University of Belfast in Northern Ireland.
"Mounting evidence now suggests that it is very important to maintain a good diet as we get older and that supplementation of diet with vitamin B complex and folate is very important to maintain good health," McIlroy told Reuters Health.
Prior research has shown that elevated levels of homocysteine may increase the risk of heart disease and stroke. 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.
McIlroy and his colleagues measured homocysteine 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.
The researchers accounted for several factors that could have influenced the risk of stroke, Alzheimer's and dementia, including education, diet, blood pressure and cholesterol levels. They also screened participants for variations of the gene MTHFR that can make it difficult to process folate.
Compared to the healthy elderly, people who had had a stroke were more than five times as likely to have elevated homocysteine, McIlroy's team reports in the October issue of Stroke: Journal of the American Heart Association ( news - web sites). The odds were increased nearly three times in people with Alzheimer's and almost five times in those with vascular dementia.
The MTHFR gene did not influence the odds of having high homocysteine, although people with certain variations of the gene did seem to be more likely to have non-Alzheimer's dementia.
What is now needed, according to McIlroy, are clinical trials that compare vitamin B and folate supplementation with a placebo, a pill that does not contain any active ingredients, to see whether supplementation can reduce the risk of stroke or dementia.
"Only controlled trials will tell us if any cases of stroke or dementia can be prevented," McIlroy said.
Since the late 1990s, the US has required that certain grain foods, including bread, cereals, flour and pasta, be fortified with folic acid, but according to McIlroy, "there is a case for further supplementation even when normal foods are fortified."
Supplementation may indeed be a good idea, according to Dr. Amos D. Korczyn of the Tel-Aviv University Medical School in Israel, even though he points out in an accompanying editorial that the jury is still out on whether high homocysteine causes stroke and dementia or is instead a consequence of these problems.
Even if a consensus is reached about homocysteine, including how often to measure it, Korczyn suggests that "it may be simpler if all older people, and particularly those with higher risk of vascular disease or dementia, receive supplemental folic acid and vitamin B12."
He continues, "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." Korczyn points out that these vitamins are inexpensive and do not cause side effects, even when excessive amounts are taken.
SOURCE: Stroke 2002;33:2351-2356, 2343-2344. |
