Randomised clinical trials have consistently shown no clear benefit of single antioxidant supplements on chronic disease risk and even potential harms of supplementation of vitamin E and β-carotene on mortality and lung cancer risk, respectively. The randomised trials have used supplements with single or a few antioxidants, whereas the observational studies have assessed these nutrients based on blood concentrations or the dietary intake of foods rich in these nutrients. The dietary sources of these antioxidants (fruits, vegetables, berries, etc.) also contain a myriad of other correlated bioactive compounds that may have synergistic bioactivities. The results from the observational studies could reflect a limited number of bioactive compounds that have not been evaluated in randomised trials or complex, interactive effects of multiple correlated beneficial food components in plant foods.
In a review on dietary intake and blood concentrations of antioxidants and the risk of cardiovascular disease, total cancer, and all-cause mortality, higher dietary intake and/or blood concentrations of vitamin C, carotenoids, and α-tocopherol (as markers of fruit, vegetable, and nut intake) were associated with reduced risk of cardiovascular disease, total cancer, and all-cause mortality. It is likely that the associations observed are not due to the individual antioxidants themselves, but rather the combination of multiple beneficial components in fruits and vegetables. These results support the notion that a high intake of fruits and vegetables, especially those high in vitamin C and carotenoids, reduces the risk of cardiovascular disease, cancer, and premature mortality.
Aune, D., et al. (2018). Dietary intake and blood concentrations of antioxidants and the risk of cardiovascular disease, total cancer, and all-cause mortality: a systematic review and dose-response meta-analysis of prospective studies. American Journal of Clinical Nutrition, vol. 108, 1069–1091.