A Framework to Guide Defining an Upper Threshold of Crystalline Vitamin B12 in Foods and Food Supplements.

PURPOSE OF REVIEW: To define an intake threshold of vitamin B12 from food supplements that is sufficient to maintain normal body functions, but it does not cause pharmacological effects.

RECENT FINDINGS: We used studies on the amount of B12 absorbed following oral B12 application and non-comparative case-series studies to synthesize evidence on pharmacological effects of oral B12 (between < 10 µg and 3000 µg) in people with manifested deficiency. There is a dose-dependent intestinal absorption of B12 and in the same time effects on body metabolism and functions. Food supplements providing ≤ 20 µg B12 daily are unlikely to cause pharmacological effects, while 50 µg might correct abnormal biochemical markers in some deficient patients. Foods for special medical purposes for people who cannot absorb B12 may contain 100 µg to 150 µg B12. This dose may ensure 1-4 µg of the vitamin reaching the circulation on a daily basis independent of intrinsic factor. Dosages ≥ 200 µg/d should be considered as drugs that can correct anemia, metabolic markers and clinical symptoms. The content of vitamin B12 in food supplements should not exceed 20 µg. In addition, people with deficiency should receive appropriate medical treatment with high dose B12.