RESUMEN
B-vitamins act as enzymatic co-factors in immune functions, therefore they are considered to reduce chemotherapy-induced side effects in cancer patients. We conducted a systematic search, screening five electronic databases (Embase, Cochrane, PsychInfo, CINAHL and Medline) to find studies on the effectiveness and potential harm of B-vitamin therapy on cancer patients. Out of the 7465 search results, 11 RCTs about vitamin B6, B12 and B-vitamins in combination were included in this systematic review. A total of 1546 patients with diverse types of cancer were evaluated. Overall, most studies were of acceptable quality and reported consistent results. Studies examining the effectiveness of vitamin B6 reported that there is no significant impact on decreasing the incidence and severity of chemotherapy-induced side effects (e.g., hand-foot syndrome), the necessity of chemotherapy dose-modifications or improving patients' quality of life, tumor response/progression, and overall survival. Two studies reported that vitamin B12 could be effective in the alleviation of symptoms resulting from chemotherapy; it might decrease motor, sensory and pain symptoms of peripheral neuropathy. However, a combination of B vitamins may not reduce the incidence of chemotherapy-induced peripheral neuropathy. All in all, the evidence on B-vitamins in cancer patients is low and supplementation cannot be recommended.