Researchers tested participants for thinking skills and blood levels of vitamin B12, as well as for the presence of blood markers that accumulate when the body does not have enough B12. Four to five years later they had MRI brain scans.
Scientists at Rush University Medical Center in Chicago found those who had the markers linked to vitamin B12 deficiency were more likely to have the smallest brains and the lowest scores on tests measuring short-term memory, concentration and other thinking processes.
As the brain ages, it begins to shrink and lose some volume. More severe brain shrinkage occurs in those with dementia, including Alzheimer's disease.
While B12 occurs naturally in beef, fish, shellfish, dairy products and many other foods, the problem often is not with diet but absorption, says Christine Tangney, associate professor of clinical nutrition at Rush and one of the study authors. Some prescription medications used to treat heartburn, stomach ulcers and type 2 diabetes can limit the absorption of B12, as can the thinning of the stomach lining, which can happen with age.
The study, published in the journal Neurology, shows that diagnosing B12 deficiency can be difficult. Indeed, all of the study participants had B12 blood levels measuring in the normal range.
Still, 15 to 17 percent had elevated levels of biomarkers indicating B12 deficiency.
"Even though the B12 in the blood may be at a certain level," Tangney says, "there may not be enough in the tissues."
"It's an important study, because it seems to suggest that just checking for serum B12 levels in elderly patients is probably not enough," says Daniel C. Potts, M.D. associate clinical professor of neurology at the University of Alabama School of Medicine in Tuscaloosa.