Antioxidants may not always be beneficial to health.

Some results from cohort investigations indicate that supplemental antioxidants cannot decrease the risks for some diseases and even can play an inverse role because the antioxidant may not be involved in metabolism or may be a pro-oxidant in vivo. Therefore, further studies are required to identify conditions of an antioxidant converting into a pro-oxidant and the pathway of an antioxidant being a metabolic component. Additionally, long-term investigations on large-scale cohorts are required in order to clarify which disease is suitable for antioxidant therapy and how antioxidant intake can really maintain health.