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Cancer survivors experience a range of side effects during and after treatment. There is a need for a rigorous synthesis of the most recent and best available evidence on the role of nutritional supplements for supportive care in cancer, to inform shared decision-making. We searched 5 databases for umbrella reviews, meta-analyses and systematic reviews on nutritional supplements for supportive cancer care, excluding studies on pain, anxiety and depression, which are covered in recent guidelines. We found 52 reviews that reported on 250 RCTs on 18 supplements for 16 indications. Almost all reviews were of low/critically low quality (assessed using A MeaSurement Tool to Assess systematic Reviews version 2). There was moderate-certainty evidence for benefit from the following supplements: amino acids and oral proteolytic enzymes for severity of radiation-induced dermatitis, N-acetyl cysteine for prevention of chemotherapy-induced peripheral neuropathy (CIPN) in individuals with gastrointestinal cancers. There was low to very low certainty evidence that glutamine, zinc, probiotics and melatonin may be effective for oral mucositis; Vitamin E, omega-3 fatty acids, glutamine and other amino acids may be effective for preventing CIPN. Serious adverse events were reported for high-dose Vitamin A, and dose-related adverse events were reported with zinc and Vitamin E. However, the majority of nutritional supplements were associated with only minor adverse events. Due to the low to very low certainty of the majority of evidence, firm clinical recommendations cannot be made. Further research to conclusively evaluate benefit and harm, including potential impact on efficacy of standard treatments, should be conducted.