In a nice follow up to an earlier study that suggested that B vitamins may reduce brain shrinkage in the elderly, new research finds that B12 may also ward off Alzheimer’s disease. This should not come as a complete surprise since brain shrinkage is strongly linked to cognitive decline including Alzheimer’s disease, but the new study adds to a growing body of evidence suggesting that what we eat may affect the health of our bodies and brains in significant ways.

The results held strong even after the researchers corrected for other variables, like age, sex, body mass index, blood pressure, smoking, and a gene thought to be linked to cognitive decline. The effect of B12 was more pronounced in older participants.

In the new study, carried out at the Karonlinska Institute in Sweden, the research team looked at both B12 levels (the active form is called holotranscobalamin) in the blood as well as homocysteine levels: previously, B12 has been shown to lower homocysteine, which itself is linked to cognitive decline. The 271 elderly participants were followed for seven years, and monitored for the development of Alzheimer’s.

The research team, led by Babak Hooshmand, found that for each incremental rise in B12 (one picomolar), the risk for Alzheimer’s decreased by 2%. For each rise in homocysteine (one micromolar), the risk for Alzheimer’s rose by 16%. The results held strong even after the researchers corrected for other variables, like age, sex, body mass index, blood pressure, smoking, and a gene thought to be linked to cognitive decline. The effect of B12 was more pronounced in older participants.

Though the study did not show causality (i.e., that B12 itself actually reduces Alzheimer’s risk), Hooshmand and colleagues say that the design of the study helps rule out, at least, reverse causality (i.e., that Alzheimer’s risk might alter B12 and homocysteine levels). According to the study, low levels of vitamin B12 and high homocysteine are "surprisingly common conditions in the elderly, both in developed and developing countries." B12 is found in animal products, like eggs, fish, and other meats. More research will be needed to determine whether B12 supplementation actually reduces the risk for Alzheimer’s, and whether it might be used to treat cognitive decline once it has already developed.

The study was published in the October 19, 2010 issue of Neurology.