Micronutrient supplementation for cancer patients. Rationale for recommendations

Vitamins, minerals, trace elements, and especially antioxidants in different combinations and concentrations are taken by 70% of oncological patients. The reasons they consume these micronutrients differ and in many cases are not justified. Multivitamin supplements within a normal range (100% of dietary reference intake) are without any risk for cancer patients; indeed, because these individuals are frequently malnourished, such supplements might be beneficial. However, antioxidants in high concentrations, which are frequently recommended, might be either beneficial or harmful. Radiotherapy and chemotherapy exert some effects on cancer cells via generation of reactive oxygen species (ROS). Antioxidants may neutralise ROS and consequently have a harmful effect regarding therapeutic efficacy. On the other hand, ROS are in part also responsible for side effects of radio- and chemotherapy, so antioxidants might be beneficial. If antioxidants are recommended to cancer patients, these factors must be kept in mind and critically analysed.