Could NAC supplements be a ‘hindrance’ for sports nutrition?

By Stephen DANIELLS

- Last updated on GMT

Could NAC supplements be a ‘hindrance’ for sports nutrition?

Related tags: Antioxidant, Inflammation, Immune system

Supplements containing N-acetylcysteine (NAC), a precursor of glutathione, may hinder muscle performance and recovery, says a new study.

Eight days of supplementation with NAC was associated with a reduction in markers of inflammation, but detrimentally affected recovery and muscle performance, according to data published in the American Journal of Clinical Nutrition​.

“This study has shown that, although redox status alterations attenuate oxidative damage and inflammation and enhance muscle performance shortly after aseptic muscle damage, it may delay its long-term recovery by interfering with intracellular signaling pathways,”​ wrote researchers from the Democritus University of Thrace in Greece.

“Therefore, our results corroborate those of previous studies suggesting that heavy use of antioxidants may have an adverse effect on muscle performance and recovery, probably by altering signaling pathways mediating muscle inflammation and recovery and potentially mitochondrial biogenesis and subsequent energy metabolism.”

A hindrance?

Commenting independently on the research, Jose Antonio, PhD, Assistant Professor of Exercise Science at Nova Southeastern University and CEO of the International Society of Sports Nutrition, told us: “According to this study, N-acetylcysteine (NAC) supplementation may indeed lessen markers of inflammation after damaging eccentric exercise.  But here's the kicker:  Over the course of several days, it actually hindered muscle performance and recovery. 

“Thus, for long term recovery, the use of these kinds of anti-oxidants may be a hindrance.”

Study details

The Greek researchers recruited 10 men and randomly assigned them to receive either placebo or NAC (20 mg/kg per day, Uni-Pharma, Greece) for eight days. They also performed muscle-damaging exercise daily.

Results showed that NAC did reduce the increase in inflammatory markers of muscle damage after exercise, including creatine kinase activity, C-reactive protein, and proinflammatory cytokines. The NAC supplement was also associated with less of strength during the first 2 days of recovery.

However, over the full eight days of the study, NAC supplementation was associated with a reduction in performance and muscle recovery.

“The NAC-enhanced GSH availability may have induced redox perturbations, down-regulating pathways mediating immune cell mobilization,” ​wrote the researchers.

“This may result in incomplete clearing of debris, which may be a prerequisite for full recovery of muscle performance.”

Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.112.049163
“Thiol-based antioxidant supplementation alters human skeletal muscle signaling and attenuates its inflammatory response and recovery after intense eccentric exercise”
Authors: Y. Michailidis, L.G. Karagounis, G. Terzis, et al. 

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