Vitamin B2: Safety

Toxicity

No toxic or adverse effects of high riboflavin intake in humans are known. Studies in cell culture indicate that excess riboflavin may increase the risk of DNA strand breaks in the presence of chromium (IV), a known carcinogen. This may be of concern to workers exposed to chrome, but no data in humans is available. High dose riboflavin therapy has been found to intensify urine color to a bright yellow (flavinuria), but this is a harmless side effect. The Food and Nutrition Board did not establish a tolerable upper level of intake (UL) when the RDA was revised in 1998.

Drug interactions

Several early reports indicated that women taking high-dose oral contraceptives (OC) had diminished riboflavin nutritional status. However, when investigators controlled for dietary riboflavin intake, no differences between OC users and non-users were found. Phenothiazine derivatives, like the anti-psychotic medication, chlorpromazine, and tricyclic antidepressants, inhibit the incorporation of riboflavin into FAD and FMN, as do the anti-malarial medication, quinacrine, and the cancer chemotherapy agent, adriamycin. Long-term use of the anti-convulsant, phenobarbitol may increase destruction of riboflavin, by liver enzymes, increasing the risk of deficiency.

Older adults (50 years of age and older)

Some experts in nutrition and aging feel that the RDA (1.3 mg/day for men and 1.1 mg/day for women) leaves little margin for error in people over 50 years of age. A recent study of independently living people between 65 and 90 years of age found that almost 25% consumed less than the recommended riboflavin intake, and 10% had biochemical evidence of deficiency. Additionally, epidemiologic studies of cataract prevalence indicate that riboflavin intakes of 1.6 to 2.2 mg/day may reduce the risk of developing age-related cataracts. Individuals, whose diets may not supply adequate riboflavin, especially those over 50, should consider taking a multivitamin/multimineral supplement, which generally provides at least 1.7 mg of riboflavin/day.