REVIEW ARTICLE Impact of Dietary Antioxidants on Sport Performance: A Review Andrea J. Braakhuis 1 • Will G. Hopkins 2 Published online: 20 March 2015 Ó Springer International Publishing Switzerland 2015 Abstract Many athletes supplement with antioxidants in the belief this will reduce muscle damage, immune dys- function and fatigue, and will thus improve performance, while some evidence suggests it impairs training adapta- tions. Here we review the effect of a range of dietary an- tioxidants and their effects on sport performance, including vitamin E, quercetin, resveratrol, beetroot juice, other food-derived polyphenols, spirulina and N-acetylcysteine (NAC). Older studies suggest vitamin E improves perfor- mance at altitude, with possible harmful effects on sea- level performance. Acute intake of vitamin E is worthy of further consideration, if plasma levels can be elevated sufficiently. Quercetin has a small beneficial effect for exercise of longer duration ( [ 100 min), but it is unclear whether this benefits athletes. Resveratrol benefits trained rodents; more research is needed in athletes. Meta-analysis of beetroot juice studies has revealed that the nitrate component of beetroot juice had a substantial but unclear effect on performance when averaged across athletes, non- athletes and modes of exercise (single dose 1.4 ± 2.0 %, double dose 0.5 ± 1.9 %). The effect of addition of polyphenols and other components to beetroot juice was trivial but unclear (single dose 0.4 ± 3.2 %, double dose -0.5 ± 3.3 %). Other food-derived polyphenols indicate a range of performance outcomes from a large improvement to moderate impairment. Limited evidence suggests spirulina enhances endurance performance. Intravenous NAC improved endurance cycling performance and re- duced muscle fatigue. On the basis of vitamin E and NAC studies, acute intake of antioxidants is likely to be benefi- cial. However, chronic intakes of most antioxidants have a harmful effect on performance. Key Points Chronic consumption of dietary antioxidants is likely harmful. An exception is chronic consumption of polyphenols such as epicatechin and resveratrol, which in combination with training appear beneficial. Acute intake of vitamin E and N-acetylcysteine may offer athletes a performance benefit around competition time. 1 Introduction During exercise, metabolism increases and oxygen uti- lization is elevated, leading to leakage of highly reactive oxygen species from mitochondria [1]. Aside from mito- chondrial leakage, contraction itself activates phospholi- pase A2, initiating a cascade of enzymes and thereby increasing reactive species [2]. Reactive oxygen species alter cell structure and function, and contribute to muscle damage, immune dysfunction and fatigue [3]. Other con- sequences of the release of exercise-induced reactive & Andrea J. Braakhuis a.braakhuis@auckland.ac.nz 1 Discipline of Nutrition, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand 2 College of Sport and Exercise Science, Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia 123 Sports Med (2015) 45:939–955 DOI 10.1007/s40279-015-0323-x