Information from the Boston Nutritional Status Survey on supplement use of B₁₂ by a free-living elderly population is given in Appendix F. For those taking supplements, the fiftieth percentile of supplemental B₁₂ intake was 5.0 µg for men and 6.0 µg for women. Approximately 26 percent of all adults reported taking a B₁₂-containing supplement in 1986 (Moss et al., 1989).

No adverse effects have been associated with excess B₁₂ intake from food or supplements in healthy individuals. There is very weak evidence from animal studies suggesting that B₁₂ intake enhances the carcinogenesis of certain chemicals (Day et al., 1950; Georgadze, 1960; Kalnev et al., 1977; Ostryanina, 1971). These findings are contradicted by evidence that increased B₁₂ intake inhibits tumor induction in the human liver, colon, and esophagus (Rogers, 1975). Some studies suggest a possible association between high-dose, parenterally administered B₁₂ (0.5 to 5 mg) and acne formation (Berlin et al., 1969; Dugois et al., 1969; Dupre et al., 1979; Puissant et al., 1967; Sherertz, 1991). However, the acne lesions were primarily associated with hydroxocobalamin rather than cyanocobalamin, the form used in the United States and Canada. Furthermore, iodine particles in commercial B₁₂ preparations may have been responsible for the acne. In conclusion, the evidence from these data was considered not sufficient for deriving a Tolerable Upper Intake Level (UL).

Studies involving periodic parenteral administration of B₁₂ (1 to 5 mg) to patients with pernicious anemia provide supportive evidence for the lack of adverse effects at high doses (Boddy and Adams, 1968; Mangiarotti et al., 1986; Martin et al., 1992). Periodic doses of 1 mg are used in standard clinical practice to treat patients with pernicious anemia. As indicated earlier, when high doses are given orally (see “Absorption”) only a small percentage of B₁₂ can be absorbed from the gastrointestinal tract, which may explain the apparent low toxicity.