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N-acetylcysteine decreases insulin sensitivity after moderate intensity exercise

B.D. Perry,1 I. Levinger,1,2 M.J. Brown,1 M.J. McKenna1 and N.K. Stepto,1,2 1School of Sport and Exercise Science Victoria University Melbourne Victoria and 2Institute of Sport Exercise and Active Living Victoria University Melbourne Victoria.

This study examined the effect of the antioxidant N-acetylcysteine (NAC) on acute insulin sensitivity after exercise in seven young, healthy participants. Moderate intensity aerobic exercise increases acute insulin sensitivity (Hawley & Lessard, 2008; Howlett et al., 2008) and recent evidence has suggested that regular antioxidant supplementation ablates the increase in insulin sensitivity seen through a structured exercise program (Ristow et al., 2009). This study thus seeks to test if an antioxidant can alter insulin sensitivity after a single bout of exercise. Seven untrained, healthy participants (22.1 ± 3.2 years of age, BMI: 24.8 ± 3 kg.m−2, VO2 peak, 50.6 ± 4 ml/kg/min) underwent a blind crossover study design, consisting of two identical trials separated by ∼14 days. In each trial NAC or saline was intravenously infused before and during sub-maximal exercise for a total of 95 minutes (62.5 ml/kg/min for 15 min, followed by 25 ml/kg/min for 80 min). During this infusion time, the participant underwent 35 minutes of passive rest, followed 60 minutes of sub-maximal exercise (55 min at 68% VO2 peak followed by 85% VO2 peak for five min) on an electronically braked cycle ergometer. After three hours rest, a hyperinsulinemic euglycemic insulin clamp was used to determine insulin sensitivity via a modified M-value (glucose infusion rate/ mean insulin concentration). NAC infusion during exercise resulted in ∼5.8% decrease in insulin sensitivity post-exercise (Figure, p = 0.041).

Figure 1

This research demonstrates that NAC alters insulin sensitivity after a single bout of intensified exercise. These data also suggest that reactive oxygen species produced during exercise have a role increasing post-exercise insulin sensitivity.

Hawley, J. & Lessard, S. (2008) Exercise training-induced improvements in insulin action. Acta Physiologica 192, 127-135.

Howlett, K., Mathews, A., Garnham, A. & Sakamoto, K. (2008) The effect of exercise and insulin on AS160 phosphorylation and 14-3-3 binding capacity in human skeletal muscle. American Journal of Physiology. Endocrinology and Metabolism 294, E401-7.

Ristow, M., Zarse, K., Oberbach, A., Klöting, N., Birringer, M., Kiehntopf, M., Stumvoll, M., Kahn, C. & Blüher, M. (2009) Antioxidants prevent health-promoting effects of physical exercise in humans. Proceedings of the National Academy of Sciences of the USA 106, 8665-70.

This study was funded by the VU Researcher Development Grant Scheme, 2009 (IL, NKS, MJM)