Successful Aging: A Neuroscientist Explores the Power and Potential of Our Lives

by Daniel J. Levitin

Vitamin B12 Vitamin B12 (cobalamin), found in meat, poultry, eggs, milk, and fish, is necessary for the production of myelin in the brain and is involved in the metabolism of every cell in the body. Vegans are prone to B12 deficiency and are advised to take supplements. As we age, our stomachs produce less gastric acid, reducing the body’s ability to absorb vitamin B12 that’s found in food, and so B12 deficiency is more common among older adults. Much B12 research has been driven by the homocysteine hypothesis. Homocysteine is a potentially toxic amino acid, and elevated levels of it are associated with cognitive impairment, Alzheimer’s disease, dementia, and cardiovascular disease. We believe that it increases oxidative stress and increases damage to DNA and that its neurotoxicity leads to cell death. B12 (along with B6 and folate) is responsible for recycling homocysteine, thereby keeping its levels in check; insufficient amounts of B12 are therefore believed responsible for a toxic buildup of homocysteine. Vitamin B12 deficiency is associated with cognitive decline, and older individuals with higher B12 levels generally perform better on cognitive tests. Of course, the mere fact that deficient levels of B12 are correlated with cognitive deficits does not mean that B12 supplementation will correct that.