Vitamin B12 deficiency is more common than doctors once thought, and experts advise that those most at risk — vegetarians and older adults — be sure to take supplemental forms of the vitamin.
Vitamin B12 is essential for maintaining healthy nerve cells and red blood cells; a deficiency in the vitamin can cause symptoms ranging from the subtle, including fatigue and mild dizziness, to the more severe, including nerve damage, anemia and dementia.
At one time, doctors thought that the only manifestation of B12 deficiency was an uncommon condition called pernicious anemia, explained Dr. Anthony L. Komaroff, a professor of medicine at Harvard Medical School in Boston. People with pernicious anemia lack a stomach protein called intrinsic factor, which allows the intestines to absorb vitamin B12.
But it has become clear in recent years that B12 deficiency is a much more widespread problem, Komaroff noted in an interview.
Unlike most vitamins, B12 occurs naturally only in animal products, including meat, poultry, fish and — in lesser amounts — eggs and dairy. Because of this, vegetarians and especially vegans — who avoid all animal products, including dairy — may have low stores of the vitamin.
The same is true of adults older than 50, as many have a thinning in the stomach lining that prevents the proper release of digestive acids. Stomach acids, Komaroff explained, are essential for “shaking loose” vitamin B12 from its food source, allowing it to be absorbed.
It’s important, Komaroff said, for vegetarians and older adults to get vitamin B12 through supplements, including multivitamins and fortified cereals. The crystalline form of B12 in pills and cereals is actually better absorbed than that found in animal products, and its absorption is not hindered by the lack of stomach acids in some older adults.
Vegetarian and vegan women who breastfeed should be especially careful to get enough vitamin B12, according to Komaroff. Deficiency in an infant can cause irreversible damage to the nervous system and serious developmental problems.
In general, women who breastfeed are advised to get 2.8 micrograms (?g) of B12 per day, slightly more than the 2.4 ?g recommended for all adults.
Vitamins, particularly those formulated for vegetarians, often contain many times the recommended daily amount of B12. Though it’s dangerous to take certain vitamins in such high doses, Komaroff noted, there is no evidence that excess B12 carries health risks.