Abstract
INTRODUCTION: The effects of antioxidant dietary supplements on response to biological therapies for cancer is unknown. We conducted a scoping review of the available systematic review evidence on this question. METHODS AND ANALYSIS: We searched six databases from inception to August 19, 2022 for systematic reviews of randomized controlled trials of antioxidant dietary supplements used by patients receiving curative chemotherapy, radiotherapy, or other biological therapy for cancer and assessing the impact of supplements on survival, treatment response, or disease progression. We focused on results from reviews at high or moderate AMSTAR-2 quality. Records were selected, data extracted, and AMSTAR-2 ratings assessed independently by two authors. RESULTS: We found 24 systematic reviews with relevant evidence. Reviews were heterogenous in cancers, treatments, and antioxidant dietary supplements assessed. Conclusions across reviews were mixed, ranging from negative to no apparent difference to positive, but always with caveats about the limited size and quality of the evidence. One review was rated 'moderate' on AMSTAR-2; it included one small trial of vitamin C and formed no firm conclusions. CONCLUSIONS: We did not find reliable systematic review evidence on the effects of antioxidant dietary supplements upon therapies for cancer. More research is necessary to inform clinical recommendations.