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Sports Medicine

, Volume 47, Issue 8, pp 1619–1636 | Cite as

Performance and Side Effects of Supplementation with N-Acetylcysteine: A Systematic Review and Meta-Analysis

Systematic Review

Abstract

Background

N-Acetylcysteine (NAC) is a promising antioxidant supplement with potential as an acute strategy to enhance performance in elite sport, but there are concerns about its side effects with high doses.

Objective

To review the current literature and evaluate the effects of NAC supplementation on sport performance and the risk of adverse effects.

Methods

The literature up to May 2016 was searched on MEDLINE (PubMed), EMBASE, SPORTDiscus, Google Scholar and Scopus databases to identify all studies investigating the effects of NAC supplementation on exercise performance and/or side effects experienced. Performance outcomes from each study were converted to the percent effect equivalent to mean power output in a time trial. All pooled analyses were based on random-effects models generated by Review Manager (RevMan) [Computer program], version 5.3 (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, 2014).

Results

A total of seven studies met criteria for inclusion in the sport performance meta-analysis, and 17 for inclusion in the side effects meta-analysis. The typical daily dose of NAC reported was 5.8 g·d−1; with a range between 1.2 and 20.0 g·d−1. The mean increase in performance was 0.29% (95% confidence interval −0.67 to 1.25). The difference in the odds ratio of side effects on NAC compared with placebo was 1.11 (95% confidence interval 0.88–1.39). The sub-analysis of NAC dose suggested an increase in side effects as the dosage of NAC increased; however, this observation requires further investigation.

Conclusions

Despite initial research publications reporting positive performance effects with NAC, at this stage it cannot be recommended further. The risk of side effects from NAC supplementation also remains unclear owing to significant variations in effects. Suboptimal reporting and documentation in the literature creates difficulties when meta-analysing outcomes and generating conclusions.

Keywords

Time Trial Performance Effect Sport Performance Elite Sport Muscle Force Production 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Compliance with Ethical Standards

Funding

No sources of funding were used to assist in the preparation of this article.

Conflict of interest

Kate Rhodes and Andrea Braakhuis declare they have no conflicts of interest relevant to the content of this review.

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Copyright information

© Springer International Publishing Switzerland 2017

Authors and Affiliations

  1. 1.Discipline of Nutrition, Faculty of Medical and Health SciencesThe University of AucklandAucklandNew Zealand

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