Plasma amino acid concentrations in healthy elderly men and women.

Postabsorptive plasma concentrations of the large neutral amino acids (LNAAs) were measured in 74 elderly (age 71 +/- 8 y) and 138 young (age 26 +/- 5 y) healthy subjects. Plasma concentrations of valine, leucine, and isoleucine were significantly lower in young females than in young males. This gender-related difference was not observed among elderly subjects because aging was associated with a significant rise in plasma LNAAs in females but not in males. Multiple-regression analysis of plasma amino acid concentrations from female subjects revealed a significant and positive effect of age on plasma valine, leucine, isoleucine, phenylalanine, and tyrosine but not on plasma tryptophan or methionine. Tryptophan was the only amino acid to exhibit a significant response to age in males, consisting of a 14% decline in the elderly subjects. Percentile ranges are presented for young and elderly females and males for each of the amino acids.