High levels of the amino acid homocysteine may increase the risk of developing Alzheimer's disease, a new study has shown. The risk of Alzheimer's disease was found to be nearly doubled in people with high levels of homocysteine.
The study raises the possibility of staving off dementia by consuming more folic acid and vitamins B-6 and B-12, which can lower homocysteine levels. But one of the study's authors emphasised that the research does not prove that lowering homocysteine levels will prevent Alzheimer's disease (New England Journal of Medicine 2002;346:476-83).
“Our study is observational and cannot be used as a basis for treatment recommendations,” said the study's lead author, Dr Sudha Seshadri of Boston University School of Medicine in Massachusetts. But the results should encourage trials to study the effects of vitamin supplements and lowering homocysteine levels on the development of dementia, she said.
Previous research has shown a similar association between high homocysteine levels and the risk of heart attack and stroke. Although no studies have shown that lowering homocysteine prevents disease, clinical trials testing that hypothesis for heart attacks and stroke are under way.
The benefits of lowering homocysteine levels on dementia have not been proved, however, and trials for Alzheimer's disease will probably now be proposed as well. The search for modifiable risk factors for the disease has been intense because there is nothing people can do about the three risk factors for the disease identified previously: age, family history, and presence of the APOE-e4 gene.
In this new study, Dr Seshadri and colleagues used data from the Framingham heart study. In the late 1980s, homocysteine levels were measured in about 1100 of the study's participants whose average age was about 75, none of whom had dementia. Eight years later, 10% had developed dementia, most of it attributable to Alzheimer's disease rather than stroke or other vascular disease.
The 30% with the highest homocysteine levels had twice the risk of developing Alzheimer's disease as people with average levels. The relative risk of Alzheimer's disease was 1.8 for each increase of one standard deviation in homocysteine values from baseline.