Abstract
Different supplement levels of nicotinic acid (NiA) (0mg for 3 days, 25mg/day for 3 days, 0mg for 1 day and 50mg/day for 3 days) were administered to five healthy men aged 19-20 years fed a niacin-controlled diet, then the blood concentration and urinary excretion of niacin derivatives were measured. Blood NAD was maintained at an almost constant level (26.2nmol/ml), independent of the dosage of NiA. The increase in the blood niacin level during the 50mg NiA administration period suggested that the maximum rate of metabolism of NiA to NAD was 40-55mg/24h. Urinary excretion of N1-methylnicotinamide (MNA), on the third day in each period was increased in proportion to the dosage level, whereas urinary niacin excretion remained unchanged relative to the observed blood niacin level. From these results, it is concluded that the rate of urinary MNA excretion could be useful as a quantitative index of niacin intake in humans, at least under the controlled experimental conditions employed here.
