Diurnal variations in nicotinamide metabolism were found in these women. The biosynthesis of nicotinamide from tryptophan seemed to be increased by cold exposure.

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SummaryUrinary output of water-soluble vitamins has been used as an indices for vita min nutrition. It has been pointed out that the coefficient variance of these values is high, especially for niacin catabolites. Thus, we investigated what kinds of stress affect the catabo lism using female subjects. The effects of cold exposure (as a typical physical stress), calcula tion exercise (a typical mental stress) and dark exposure (a typical emotional stress) on the metabolism of niacin were investigated. Of the stresses, cold exposure significantly increased urinary excretory output of the niacin metabolites. The biosynthesis of nicotinamide from Trp seemed to be increased by cold exposure.

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