[Vitamin supplements in oncology -- necessary, useful or superfluous?]

Vitamins are essential components of a normal diet, and sufficient amounts are always needed. Occasionally, multivitamin supplements may make sense in cancer patients. However, because of the balance of (antioxidant) vitamins, coenzymes, trace elements and secondary phytochemicals it offers, a varied diet of fresh fruits and vegetables is--wherever possible--to be preferred to supplements of single or combinations of vitamins. Although preclinical studies have confirmed the positive effects of high-dose vitamins on cancer, there is currently no evidence that increased consumption of vitamins benefits cancer patients--nor is the dose necessary to achieve a possible therapeutic impact known. Since a number of clinical and epidemiological studies fail to show any benefit, and adverse effects have even been reported, high-dose vitamins can at present be recommended only for short-term substitution in known vitamin deficiencies. Before a definitive pronouncement can be made, therefore, further clinical studies of megavitamins in cancer patients are needed.