Cobalamin (Vitamin B12): Safety Assessment

The United Kingdom Expert Group on Vitamins and Minerals (EVM) last evaluated vitamins and minerals for safety in 2003 and set a so-called Safe Upper Level (SUL) or Guidance Level for each micronutrient, provided sufficient data were available. This SUL or Guidance Level reflects the safe maximum amount of a micronutrient that will not cause any side effects when taken daily from all sources for a lifetime.

This value applies to adults 19 years of age and older and considers only the intake of vitamin B12 from dietary supplements in addition to conventional dietary intake. It does not apply to pregnant or lactating women because of a lack of studies.

To date, no adverse side effects of excessive vitamin B12 intake, both from conventional diet and supplements, have been observed.

The data from the NVS II (National Nutrition Survey II, 2008) on the daily intake of vitamin B12 from all sources (conventional diet and supplements) indicate that an amount of 2,000 µg of vitamin B12 per day is far from being reached.

Numerous studies have found no adverse effects for the various forms of vitamin B12 (cyanocobalamin, hydroxycobalamin, and methylcobalamin) in large amounts. Daily intake of cyanocobalamin in amounts of 4,500 µg over two weeks, 2,000 µg over one year, and 1,000 µg over several years remained without any discernible side effects. No adverse effects were also observed when taking 300 µg of hydroxycobalamin daily for one year and 6,000 µg of methylcobalamin daily for 12 weeks. High-dose oral vitamin B12 therapy at 5,000 µg per month taken for five years also showed no adverse effects.

The safety of vitamin B12 even at high doses can be attributed, among other things, to the fact that the absorbable amount in the intestine is physiologically limited and cannot be increased at will. That is, with an excessive intake, only a small portion is actually absorbed.