That older people have lower vitamin B12 levels is beyond dispute as this has been well documented since the early 1950's when it was shown that B12 levels were lower in 51-70 year olds when compared with 15-40 year olds, and those over 71 had even lower vitamin B12 levels. The question is whether this is a 'normal' feature of aging.  If it was a normal 'physiologic' phenomenon, then the biochemical indicator of cellular B12 adequacy (MMA) would not be abnormal in up to 75% in this population and improve after B12 supplementation. Abnormalities of gastric function are responsible for the lion's share of low B12 levels in older individuals and the most common cause is Food-Cobalamin Malabsorption (FCM) which is the result of decreased stomach acid production needed to split vitamin B12 from its protein dietary source. If B12 cant be freed from dietary protein, then it cannot be picked up by Intrinsic Factor and escorted to the B12 receptor in the distal small bowel (ileum) for absorption.