High homocysteine tied to Alzheimer's. (Biomedicine).

For the first time, research has linked the incidence of Alzheimer's disease and other forms of dementia to elevated blood concentrations of the amino acid homocysteine. Scientists had previously connected high homocysteine concentrations to heart disease and stroke, maladies associated a heightened risk of Alzheimer's disease and other dementias. Also, a few scientists had already noted high homocysteine concentrations in the blood of Alzheimer's patients.

The earlier observations didn't prove a link between homocysteine and Alzheimer's disease, however, because blood homocysteine is affected by diet and many people with dementia don't eat well, says neurologist Sudha Seshadri of Boston University School of Medicine.

Seshadri and her colleagues sought clarity on the issue by examining blood samples obtained 8 years apart from 935 people enrolled in the long-term, ongoing Framingham Heart Study in Massachusetts.

At the time the first sample was taken, none of the volunteers--average age 76--had Alzheimer's disease or any other dementia. But 30 percent had homocysteine measuring more than 14 micromoles per liter of blood, which is considered high by doctors. After 8 years, 111 people in the study had developed some form of dementia; 83 of them were diagnosed with apparent Alzheimer's disease.

The participants who tested high for homocysteine at the beginning of the study were nearly twice as likely as the others to develop dementia, including Alzheimer's, the researchers report in the Feb. 14 New England Journal of Medicine.

The study doesn't prove that homocysteine causes Alzheimer's disease, says Neil S. Buckholtz, a neuroscientist at the National Institute on Aging in Bethesda, Md. But he says the findings raise an important question: Since taking vitamins [B.sub.6], [B.sub.12], or folic acid can slash homocysteine concentrations in the blood, might they also lessen the risk of Alzheimer's disease?--N.S.