Antioxidant Supplements: More Hype Than Benefit

Astaxanthin is the latest “super antioxidant” being promoted on social media to reduce inflammation, boost metabolism, and enhance athletic performance. Is there any evidence to support the use of antioxidant supplements for overall health benefits or improve athletic performance?

The theory sounds reasonable. Exercise increases the production of free radicals, chemically reactive molecules which can damage cell membranes and DNA. Antioxidants such as vitamins C and E neutralize these molecules, potentially reducing muscle damage and inflammation. But free radicals also serve an important physiological purpose, acting as signals that stimulate the body's adaptations to exercise. Suppressing these signals might actually interfere with the benefits of training.

Large randomized trials have failed to demonstrate that antioxidant supplements prevent cardiovascular disease, cancer, or premature death. A pooled review of 78 randomized trials found that antioxidant supplementation did not reduce mortality. In fact when investigators pooled the results of the more methodologically reliable trials, they found an overall 4% increase in mortality. Beta-carotene, vitamin A, and high-dose vitamin E were among the supplements associated with potential harm. Note that these studies used refined supplements and do not apply to antioxidants consumed naturally in fruits and vegetables.

How about muscle soreness (DOMS)? A review of 50 trials found that high-dose antioxidant supplements produced measurable but clinically insignificant reductions in muscle soreness. At 48 hours after exercise, soreness was reduced by only 0.41 points on a 10-point pain scale. Other reviews found reductions in certain blood markers of oxidative stress and inflammation, but without meaningful improvements in muscle soreness or strength. Improving a blood test is not the same as improving recovery.

In fact, high-dose antioxidant supplements may interfere with training adaptations. Free radicals generated during exercise activate the cellular signaling pathways involved in mitochondrial development and muscle adaptation. A 2020 review of the impact of antioxidant supplementation on exercise performance found little convincing evidence that routine supplementation improved athletic performance and actually raised concerns about interference with training adaptations. However, evidence that these effects consistently translate into reduced performance gains is limited.

The bottom line: Antioxidant supplements have not demonstrated benefits for preventing major chronic diseases or meaningful improvements in post-exercise muscle soreness or athletic performance. Instead, high doses may interfere with some of the adaptations we are trying to achieve through training.

The best approach would appear to be obtaining your antioxidants from whole foods, which also contain a number of other potentially beneficial biologically active compounds, including phytochemicals.

For cyclists, the practical message is straightforward: eat a balanced diet rich in fruits and vegetables, but don't assume that taking extra antioxidants will make you healthier, recover faster, or ride stronger.