Determination of the Tolerable Upper Intake Level of Leucine in Healthy Elderly (70‐75y)

Abstract

Leucine, a branched‐chain amino acid, has been shown to stimulate muscle protein synthesis, and thus it has been proposed to prevent age related muscle atrophy (sarcopenia). Therefore, leucine supplementation may have potential benefits in elderly populations. The UL (tolerable upper intake level) for leucine intake in young men has been recently determined to be 500 mg/kg/day, and increases in ammonia concentrations were seen at intake levels above 500/mg/kg/day. The objective of the current study was to determine the UL for leucine in healthy elderly men, as this is currently unknown. Five healthy elderly men (70 – 76 yrs) received graded stepwise increases in leucine intakes ranging from 50 ‐ 650 mg/kg/day, provided on eight separate study days. The UL of leucine was identified by measurements of plasma and urinary biochemical variables, including blood ammonia, glucose and insulin concentrations. Further, the participants received an oral primed‐continuous protocol of 1‐13C‐leucine on all study days to measure changes in leucine oxidation. None of the participants reported any adverse physical symptoms on study days. Leucine oxidation appears to plateau with increasing leucine intakes. Blood ammonia concentrations above normal values (35 µmol/L) were observed at leucine intake of 350mg/kg/day and above. Plasma glucose stayed within normal ranges. These preliminary results suggest that the UL for leucine in healthy elderly men may be lower than the current UL of 500 mg/kg/d for healthy young men.(Supported by ICAAS)