The idea that dietary supplements can improve athletic performance is popular 
among athletes. The use of antioxidant supplements is widespread among endurance 
athletes because of evidence that free radicals contribute to muscle fatigue 
during prolonged exercise. Furthermore, interest in vitamin D supplementation is 
increasing in response to studies indicating that vitamin D deficiency exists in 
athletic populations. This review explores the rationale for supplementation 
with both antioxidants and vitamin D and discusses the evidence to support and 
deny the benefits of these dietary supplements. The issue of whether athletes 
should use antioxidant supplements remains highly controversial. Nonetheless, at 
present there is limited scientific evidence to recommend antioxidant 
supplements to athletes or other physically active individuals. Therefore, 
athletes should consult with their health care professional and/or nutritionist 
when considering antioxidant supplementation. The issue of whether athletes 
should supplement with vitamin D is also controversial. While arguments for and 
against vitamin D supplementation exist, additional research is required to 
determine whether vitamin D supplementation is beneficial to athletes. 
Nevertheless, based upon the growing evidence that many athletic populations are 
vitamin D deficient or insufficient, it is recommended that athletes monitor 
their serum vitamin D concentration and consult with their health care 
professional and/or nutritionist to determine if they would derive health 
benefits from vitamin D supplementation.