Dietary or supplemental intake of antioxidants and the risk of mortality in older people: A systematic review

Purpose Antioxidants have a protective role in the prevention of cancer, cardiovascular disease and all-cause mortality. The association between dietary or supplemental intake of various antioxidants and all-cause mortality or cause-specific mortality among older populations is inconclusive. This systematic review aimed to systematically evaluate whether higher dietary or supplemental intake of antioxidants can lower the risk of all-cause mortality or cause-specific mortality in the older population. Methods Five electronic databases were searched to identify studies that evaluated the effects of dietary or supplemental intake of antioxidants on cause-specific or all-cause mortality in the older population aged >= 65 years. The overall quality of the evidence was assessed using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system. Twenty-two longitudinal, prospective observational studies and randomised controlled trial (RCT) studies involving 1 090 844 cases of cause-specific and all-cause mortality were included. The overall quality of studies was high with a low risk of bias. Result Of the 22 studies, 16 were observational studies and 6 were RCTs. The overall quality of evidence for observational studies and RCTs were rated down as low (due to very serious risk of bias and indirectness) and moderate (due to unable to rule out publication bias), respectively. Nine studies showed significant decreases, four found significant increases and nine reported no association between antioxidant intake and risk of mortality. Conclusion There was inconclusive evidence on the associations between dietary or supplemental intake of antioxidants and mortality in the older population. More clinical trials are required to confirm the associations.