Nutritional supplements are widely used among patients with
cancer who perceive them to be anticancer and antitoxicity agents. Large-scale, randomized
cancer prevention trials have mainly been negative, with some notable adverse and beneficial effects. For example, these trials showed that
beta-carotene increases the risk of lung and
stomach cancer,
vitamin E increases
prostate cancer and colorectal
adenoma, and
selenium reduces gastric and
lung cancer in populations with low
selenium levels but increase rates in those with higher levels. Both
beta-carotene and
vitamin E supplementation increase overall mortality. This article reviews phase II and III trials that examine the effects of multivitamins,
antioxidants,
vitamin D, and n-3 supplements on outcome and toxicity from
cancer treatments. Although
vitamin E and
beta-carotene reduce toxicity from
radiotherapy among patients with
head and neck cancer, it has been found to increase recurrence, especially among smokers.
Antioxidants have mixed effects on
chemotherapy toxicity, but there are no data on outcome.
Vitamin D deficiency is relatively common among patients with
cancer, and ongoing phase III trials are studying the effect of
vitamin D on outcome as well as optimum
vitamin D and
calcium intakes for bone health. Docosahexanoic and eicosopentanoic
acid supplements have mixed effects on
cachexia and are currently being tested as potential adjuncts to maximize response to
chemotherapy. Nutritional supplementation tailored to an individual's background diet, genetics,
tumor histology, and treatments may yield benefits in subsets of patients. Clinicians should have an open dialogue with patients about nutritional supplements. Supplement advice needs to be individualized and come from a credible source, and it is best communicated by the physician.