A preliminary study carried out in Poland showed that, in comparison with young healthy female adults, centenarians living in Upper Silesia had significantly higher red blood cell glutathione reductase and catalase activities, although serum levels of vitamin E were not significantly higher. Researchers in Denmark have also found that centenarians exhibit a high activity of glutathione reductase in red blood cells. In this study, the centenarians having the best cognitive and physical functional capacity tended to have the highest activity of this enzyme.
Some patients exhibit deficient levels of glutathione activity as a result of not consuming enough riboflavin in their diets.
Riboflavin is a precursor for FAD, whose reduced form donates two electron to the disulfide bond which is present in the oxidized form of glutathione reductase in order to begin the enzyme's catalytic cycle. In 1999, a study found that 17.8% of males and 22.4% of females examined in Saudi Arabia suffered from low glutathione reductase activity due to riboflavin deficiency.
Free riboflavin is naturally present in foods along with protein-bound FMN and FAD. Bovine milk contains mainly free riboflavin, with a minor contribution from FMN and FAD. In whole milk, 14% of the flavins are bound noncovalently to specific proteins.
Egg white and egg yolk contain specialized riboflavin-binding proteins, which are required for storage of free riboflavin in the egg for use by the developing embryo.
Reduction of the oxidized form of glutathione (GSSG) to its reduced form (GSH) by Glutathione reductase is FAD dependent. In humans, there is no evidence for riboflavin toxicity produced by excessive intakes, in part because it has lower water solubility than other B vitamins, because absorption becomes less efficient as doses increase, and because what excess is absorbed is excreted via the kidneys into urine. Even when 400 mg of riboflavin per day was given orally to subjects in one
study for three months to investigate the efficacy of riboflavin in the prevention of migraine headache, no short-term side effects were reported.
Liver, cooked, pan-fried Riboflavin: 5mg per 100g
