Biochemical markers for assessment of niacin status in young men: urinary and blood levels of niacin metabolites.
Biochemical markers of niacin status were studied in healthy young men fed 6.1 to 32 niacin equivalents (NE) per day over an 11-wk period while residing in a metabolic unit. Methylated metabolites of niacin, N1-methylnicotinamide (NMN) and N1-methyl-2-pyridone-5-carboxamide (2-pyr), in urine and plasma were determined during periods of low (6.1 or 10.1 NE per day), adequate (19 NE per day = 1 RDA) and high (25 or 32 NE per day) niacin intakes and after small test doses of nicotinamide. Urine excretion of less than 1.2 mg/d of either NMN or 2-pyr was a reliable indicator of subjects receiving the lowest intake of 6.1 NE/d, but the NMN metabolite was a better marker of subjects ingesting 10.1 NE/d. The ratio of 2-pyr/NMN in urine was not as good a measure of the 6.1 NE/d intake as the individual metabolite excretions and was not responsive to the 10.1 NE/d intake. Plasma niacin metabolites were generally not as reliable as urinary metabolites for identifying subjects receiving low niacin intakes, however, values for plasma 2-pyr dropped quickly and were eventually nondetectable. After a 1 RDA oral dose of nicotinamide, increases in urine and plasma 2-pyr levels above pre-dose baseline values were significantly decreased in subjects receiving low, as compared to adequate, niacin intake. A leucine supplement had no effect on the rate of repletion of niacin-deficient subjects nor on the level of methylated niacin metabolites in urine or plasma.
Jacob
R A
RA
U.S. Department of Agriculture, Western Human Nutrition Research Center, San Francisco, CA 94129.
Swendseid
M E
ME
McKee
R W
RW
Fu
C S
CS
Clemens
R A
RA
D000328:Adult; D015415:Biomarkers; D006801:Humans; D007700:Kinetics; D008297:Male; D009525:Niacin / Q000008:administration & dosage / Q000378:metabolism* / Q000493:pharmacokinetics; D009536:Niacinamide / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000097:blood / Q000652:urine; D009752:Nutritional Status
D015415:Biomarkers; D009536:Niacinamide; D009525:Niacin; C005211:N'-methyl-2-pyridone-5-carboxamide; C024058:N(1)-methylnicotinamide