Potential Harms Of Antioxidants
by Doug Stewart
Why the consumption of large amounts of antioxidants does not counteract the damaging effects of oxidative mitochondrial stress
You may have heard of free radicals, oxidative stress and antioxidants. But what are these really and is it true that free radicals are bad, and antioxidants are good, no matter what?
Free radicals are unstable atoms that can damage our cells or cause illness and they are also responsible for aging. Little is known about their role in human health, but in general there is the notion that they are a problem, especially when they overwhelm the body’s ability to regulate them. This is what is referred to as oxidative stress.
While our body produces free radicals during normal metabolic processes, it also produces antioxidants that neutralise these free radicals so that they do not cause harm.
As the word implies, antioxidants inhibit oxidation, the chemical reaction that can produce the free radicals. They can be found in our nutrition, especially in fruits and vegetables: vitamin C, vitamin E, Selenium and carotenoids. Certain levels of antioxidants are required for good health, but there is still a debate on whether large amounts of antioxidant-rich foods or supplements are beneficial. Synthetic antioxidants have been reported to be dangerous for human health. Albeit a bit dated, Lobo et al. published an insightful review about this in 2010.
Vigorous exercise, such as endurance running, causes oxidative stress. Free radicals harm skeletal muscles and promote muscle fatigue (Munoz et al, 2017). It is widely believed that antioxidants can counterbalance this. Consequently, some athletes consume high doses of antioxidants in the belief that this will offset the damaging effects of the oxidative stress (e.g., Rodriguez et al. 2009, Sobal et al, 1994).
However, there is currently no convincing evidence to support the benefits of antioxidant supplementation in acute physical exercise and training. On the contrary, the consumption of large amounts of antioxidants hampers important physiological functions of free radicals needed for cell signalling. In fact, it is likely that the negative effects of high doses of antioxidant supplementation exceed their potential benefits. A study published in June this year discusses some proposed pathways of potential side effects of exogenous antioxidant supplementation in athletes.
The study reviewed existing evidence on the role of antioxidants and oxidative stress in athletes and, amongst others, looked at 13 studies that investigated the use of high doses of antioxidant supplementation on exercise adaptation in athletes. Their key findings were:
The effect of the consumption of antioxidants is dose-related: lower doses have positive effects, and higher doses have negative effects. The latter occur at doses 5-17 times higher than the RDA (Recommended Daily Allowance). Doses around the RDA seem to be sufficient to keep the oxidative stress at bay, even for competitive endurance athletes (more details on the dosages can be found in this paper).
Ingesting high doses of antioxidants can have negative effects on athletes’ training adaptation. For example, it was found that the supplementation with ascorbic acid to prevent delayed-onset muscle soreness after exercise does not preserve muscle function, but hinders the recovery process, thereby being detrimental to future performance.
Long-term administration of high doses of antioxidants reduces exercise-induced physiological adaptations such as mitochondrial biogenesis, improved antioxidant capacity, increased insulin sensitivity, and muscle hypertrophy – all of these being essential components of good sports performance.
In summary, it looks like antioxidant supplements are, in general, useless if getting your RDA through your diet for most athletes. The consumption of large amounts of antioxidants could even hamper or prevent performance-enhancing and health-promoting training adaptation such as mitochondrial biogenesis, skeletal and cardiac muscle hypertrophy, and improved insulin sensitivity.
Obviously, every individual is different, and it is always advised that you speak to a trained medical professional prior to any changes to diet or supplementation.
References:
Li S, Fasipe B, Laher I. Potential harms of supplementation with high doses of antioxidants in athletes. J Exerc Sci Fit. 2022 Oct;20(4):269-275. doi: 10.1016/j.jesf.2022.06.001. Epub 2022 Jun 11. PMID: 35812825; PMCID: PMC9241084.
D. Muñoz, G. Barrientos Vicho, J. Alves Vas, et al. Oxidative stress, lipid peroxidation indexes and antioxidant vitamins in long and middle distance athletes during a sport season. J Sports Med Phys Fit, 58 (12) (2017), pp. 1713-1719
Lobo V, Patil A, Phatak A, Chandra N. Free radicals, antioxidants and functional foods: Impact on human health. Pharmacogn Rev. 2010;4(8):118-126. doi:10.4103/0973-7847.70902
American Dietetic Association; Dietitians of Canada; American College of Sports Medicine, Rodriguez NR, Di Marco NM, Langley S. American College of Sports Medicine position stand. Nutrition and athletic performance. Med Sci Sports Exerc. 2009 Mar;41(3):709-31. doi: 10.1249/MSS.0b013e31890eb86. PMID: 19225360.
Sobal J, Marquart LF. Vitamin/mineral supplement use among athletes: a review of the literature. Int J Sport Nutr. 1994 Dec;4(4):320-34. doi: 10.1123/ijsn.4.4.320. PMID: 7874149.
Mason SA, Trewin AJ, Parker L, Wadley GD. Antioxidant supplements and endurance exercise: Current evidence and mechanistic insights. Redox Biol. 2020 Aug;35:101471. doi: 10.1016/j.redox.2020.101471. Epub 2020 Feb 20. PMID: 32127289; PMCID: PMC7284926.
Gomez-Cabrera MC, Ristow M, Viña J. Antioxidant supplements in exercise: worse than useless? Am J Physiol Endocrinol Metab. 2012 Feb 15;302(4):E476-7; author reply E478-9. doi: 10.1152/ajpendo.00567.2011. PMID: 22307485.
Close GL, Ashton T, Cable T, Doran D, Holloway C, McArdle F, MacLaren DP. Ascorbic acid supplementation does not attenuate post-exercise muscle soreness following muscle-damaging exercise but may delay the recovery process. Br J Nutr. 2006 May;95(5):976-81. doi: 10.1079/bjn20061732. PMID: 16611389.