We require vitamin B12 for proper red blood cell formation, various neurological functions, DNA synthesis, and much more. Vitamin B12 deficiency is a serious issue, especially for the elderly, partly because we produce lower levels of stomach acid when we age. In food, vitamin B12 is bound to protein and requires the activity of hydrochloric acid and gastric protease to liberate the B12, thereby enabling absorption.1
The Food and Nutrition Board at the Institute of Medicine (IOM) recommends 2.4 mcg of B12 daily for adults and children 14 years or older. According to the National Health and Nutrition Examination Survey (NHANES), mean daily B12 intake for the US population is 3.4 mcg.2 Although most people are above the recommended intake level, a significant segment of the population may be B12 deficient.
The Framington Offspring Study, for example, found B12 deficiency rates to be similar among adults in three different age groups (26–49 years, 50–64 years, and 65 years and older).3 According to the study, nearly two fifths of the population (39%) has plasma B12 levels in the “low normal” range or lower.
A primary consequence of insufficient B12 is vitamin deficiency anemia, also known as megaloblastic anemia or pernicious anemia.4 Vitamin deficiency anemia is different from the anemia caused by insufficient iron, but is no less serious. Vitamin deficiency anemia is characterized by immature or incomplete red blood cells, which crowd out healthy red blood cells.
Red blood cells transport oxygen throughout the body and without sufficient supplies, various tissues and organs are under-served. Symptoms of vitamin deficiency anemia include fatigue, muscle weakness, loss of appetite, diarrhea, and numbness or tingling of the hands and feet.
Vitamin B12 deficiency is also suspected to promote various neurological disorders, including depression and dementia.5 Researchers have observed associations between low B12 and depression, both among severely depressed patients and the general population, but haven’t identified a causal mechanism.6 If there is one, however, it probably involves homocysteine.
Homocysteine is a metabolite of the amino acid methionine. Influenced by dietary and genetic factors, homocysteine is normally present in the blood. At elevated levels, however, it’s a risk factor for scores of diseases and conditions, including cardiovascular disease, stroke, osteoporosis, infertility, depression, and dementia. Increased homocysteine is a functional marker of B12 (as well as folate) deficiency.7 According to a 2005 study published in the Journal of Psychopharmacology, “There is now substantial evidence of a common decrease in serum/red blood cell folate, serum vitamin B12 and an increase in plasma homocysteine in depression.”8
