January 18, 2006

Study Questions Advice on Vitamin B-12 Intake

NEW YORK -- The recommended daily intake for vitamin B-12 should be more than doubled from the current level, researchers argue in a new report.

In a study of 98 middle-aged and older women, the researchers found that 6 micrograms of B-12 per day seemed to be enough to prevent signs of mild B-12 deficiency. That compares with the current recommended dietary allowance (RDA) of 2.4 micrograms per day.

The findings, along with those from several past studies, "strongly suggest" that the RDA should be raised, the researchers report in the January issue of the American Journal of Clinical Nutrition.

Dr. Mustafa Vakur Bor at the University Hospital of Aarhus in Denmark led the study.

Vitamin B-12 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 more severe complications like nerve damage, anemia and even dementia.

Though the typical Western diet provides people with far more than the current RDA for B-12, certain individuals are at risk for a deficiency.

Unlike most vitamins, B-12 occurs naturally only in animal products, including meat, poultry, fish and, in lesser amounts, eggs and dairy. So vegetarians and 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 are essential for "shaking loose" vitamin B-12 from its food source, allowing it to be absorbed. So older adults are advised to get their B-12 from pills and fortified foods like cereal; the synthetic version of the vitamin is more readily absorbed than the natural form.

But there has been debate as to whether the RDA of 2.4 micrograms is too low, Vakur Bor and his colleagues note in their report.

That RDA is what experts believe is the minimum B-12 needed to prevent anemia, nerve damage and mental dysfunction. But it's not clear that it's enough to prevent subtler effects, according to the researchers.

In their study, they looked at the relationship between vitamin B-12 intake and certain blood markers of mild B-12 deficiency in 98 postmenopausal women.

Based on diet records the women kept for one week, Vakur Bor and his colleagues separated them into groups according to B-12 intake. They found that overall, 6 micrograms of B-12 per day appeared to be enough to normalize the various blood markers of B-12 status.

This suggests, the researchers conclude, "that this dose might be more adequate for the general population than the current RDA of 2.4 micrograms."

SOURCE: American Journal of Clinical Nutrition, January 2006.