B-12 & the brain

People with low blood levels of vitamin B-12 a decade earlier were more likely to score poorly on a test that's widely used to screen for early signs of dementia.
However, the usual blood test for vitamin B-12 wasn't sensitive enough to detect a link. It appeared only when researchers looked at methylmalonic acid (which goes up when the body has too little B-12) or holotranscobalamin (the active part of B-12).
What to do: People aged 55 or older can lose the ability to absorb the B-12 that's bound naturally to protein, so they should take a multivitamin or eat fortified foods with at least 6 micrograms of vitamin B-12 (that's the Daily Value).
This study isn't proof that lower B-12 levels lead to memory loss, but severe B-12 deficiency can cause irreversible neurological damage that looks like AIzheimer's disease.