The Effects of Short-Term N-Acetylcysteine Supplementation on Biochemical Parameters in Endurance-Trained Adults: A Randomized Clinical Trial.

Background: The main aim of this study was to assess the effects of short-term N-acetylcysteine (NAC) supplementation on concentrations of homocysteine (Hcy) and reduced glutathione (rGSH), blood lipid profile and liver enzyme activities in endurance-trained adults, and to determine whether these effects are modified by methylenetetrahydrofolate reductase (MTHFR) C677T and glutathione S-transferase Pi 1 (GSTP1) A313G. Methods: A total of 56 males and 21 females completed a randomized, double-blind, placebo-controlled crossover trial. Participants received 1200 mg of NAC or a placebo for seven days in a crossover design. Serum Hcy and plasma rGSH concentrations were assessed using dedicated biochemical assays, while blood lipid profile and liver enzyme activities were measured using the biochemical analyzer Konelab 20i. Genotyping was conducted using TaqMan probes. A series of within-subject/between-subject repeated-measures analysis of variance (ANOVA) within a general linear model framework were performed to compare Hcy, rGSH, blood lipid profile and liver enzymes activities before and after the intervention. Results: Hcy concentrations significantly decreased following NAC supplementation (18.58 ± 5.45 µmol/L vs. 16.51 ± 4.97 µmol/L; p = 0.009), although subgroup analysis indicated that the decrease was significant only among females (15.40 ± 4.96 µmol/L vs. 13.60 ± 3.68 µmol/L; p = 0.002) without any significant effect among males. We did not observe any significant changes in rGSH, lipid profile, or liver enzyme activities. There was no interaction between NAC supplementation, MTHFR and GSTP1 genotypes and the changes noted in the parameters we analyzed. Conclusions: In conclusion, short-term NAC supplementation may reduce circulating Hcy concentrations in endurance-trained adults, particularly in females. No consistent effects were observed for rGSH, lipid profile, or liver enzyme activities.