Riboflavin: Béda antarrépisi

Glutathione reductase is an FAD-dependent enzyme that participates in the redox cycle of glutathione. The glutathione redox cycle plays a major role in protecting organisms from reactive oxygen species, such as hydroperoxides.

Glutathione peroxidase, a selenium-containing enzyme, requires two molecules of reduced glutathione to break down hydroperoxides (see diagram).

Age-related cataracts are the leading cause of visual disability in the U.S. and other developed countries. Research has focused on the role of nutritional antioxidants because of evidence that oxidative damage of lens proteins from light may lead to the development of age-related cataracts. Two case-control studies found significantly decreased risk of age-related cataract (33% to 51%) in men and women in the highest quintile of dietary riboflavin intakes (1.6 to 2.2 mg/day) compared with those in the lowest quintile (0.08 mg/day) (16). Individuals in the highest quintile of riboflavin nutritional status, as measured by red blood cell glutathione reductase activity, had approximately one half the occurrence of age-related cataract as those in the lowest quintile of riboflavin status, though the results were not statistically significant (17). Recently, a cross-sectional study of 2,900 Australian men and women, 49 years of age and older, found that those in the highest quintile of intake for riboflavin were 50% less likely to have cataracts than those in the lowest quintile (18). A prospective study of more than 50,000 women did not observe a difference between rates of cataract extraction between women in the highest quintile of riboflavin intake (1.5 mg/day) and those in the lowest quintile (1.2 mg/day) (19). However, the range between the highest and lowest quintiles was small, and median intake levels for both were above the current RDA for riboflavin. Although these observational studies provide support for the role of riboflavin in the prevention of cataracts, placebo-controlled intervention trials are needed to confirm the relationship.

The most common forms of riboflavin available in supplements are riboflavin and riboflavin 5'-monophosphate. Riboflavin is most commonly found in multivitamin and vitamin B-complex preparations (23).

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 (24). 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 (1).