Systematic review of branched-chain amino acid supplementation high in leucine on interleukin-6

Background: Inflammation-induced muscle catabolism and atrophy are well-documented phenomena often associated with elevated interleukin-6 (IL-6) levels. Branched-chain amino acids (BCAA), especially leucine, play essential roles in suppressing IL-6 expression and secretion through the mammalian target of rapamycin (mTOR) signaling pathway, and their administration is known to enhance muscle recovery. Aims: This review explores the impact of branched-chain amino acid supplementation on inflammation, explicitly focusing on interleukin-6 levels. Methods: The literature search was conducted across the Embase, Cochrane, PubMed, and Scopus databases using search terms such as ((((BCAA administration) OR (branched-chain amino acid administration)) OR (leucine administration)) AND (interleukin 6)) OR (IL 6). The articles published between 2013 and 2023 were selected. The quality of the included studies was assessed using the Oxford Centre for Evidence-Based Medicine and the Jadad Scale. Results: Thirteen studies involving 770 subjects were included in the analysis. Results revealed variability in the effects of BCAA on IL-6 levels. Some studies reported significant impacts, while others did not. Notably, post-exercise IL-6 levels increased in most cases, and BCAA supplementation was suggested to attenuate this response potentially with variation of dosage, intervention forms, and duration. Conclusion: BCAA supplementation toward IL-6 levels is still ambiguous, yet potential benefits were suggested. Future investigations are needed to refine our understanding of the complex interplay between BCAA and IL-6 and for near-future clinical recommendations.