Niacin vitamin high intakes

Riboflavin in its coenzyme forms (FMN and FAD) plays key metabolic roles in biological oxidation-reduction reactions involving carbohydrates, amino acids and lipids, and in energy production via the respiratory chain. These coenzymes also act in cellular metabolism of other water-soluble vitamins through the production and activation of folate and pyridoxine (vitamin Bg) to their respective coenzyme forms and in the synthesis of niacin (vitamin B3) from tryptophan. In addition, some neurotransmitters and other amines require FAD for their metabolism. Recently, Chocano-Bedoya et al. (2011) suggested a possible benefit of high intakes of riboflavin (about 2.5 mg/ day) from food sources on the reduction of incidence of premenstrual syndrome. 

Along with increasing evidence of health benefits from consumption of vitamins at levels much higher than RE) A recommendations comes concern over potential toxicity. This topic has been reviewed (19). Like all chemical substances, a toxic level does exist for each vitarnin. Traditionally it has been assumed that all water-soluble vitamins are safe at any level of intake and all fat-soluble vitamins are toxic, especially at intakes more than 10 times the recommended allowances. These assumptions are now known to be incorrect. Very high doses of some water-soluble vitamins, especially niacin and vitamin B, are associated with adverse effects. In contrast, evidence indicates that some fat-soluble micronutrients, especially vitamin E, are safe at doses many times higher than recommended levels of intake. Chronic intakes above the RDA for vitamins A and D especially are to be avoided, however. 

The individual vitamin demand varies widely and is also dependent on the personal constitution. Stressful situations and e.g. pregnancy require a higher vitamin intake. For men, the recommended daily dose of Vitamin A, Bj, B2, Bg, K and niacin is usually higher than for women. There are series of studies, which confirm the breadth of application and the tolerability of vitamins and other micronutrients. The pharmacological effects with high doses of antioxidant provitamins and vitamins (especially )S-carotene and Vitamins C and E) in the treatment of cardiovascular and other diseases have been encouraging, albeit further controlled clinical studies will be needed to substantiate these observations. 

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