Ask the Doctor

Spring 2007

Dr. Ashish Kamat, Assistant Professor, Urology & Cancer Biology at the University of Texas-MD Anderson Cancer Center answered these questions for us.

Q. A recent study released in the Journal of the American Medical Association said that the use of beta carotene, vitamin A, and vitamin E may increase mortality, perhaps in cancer patients. Please comment on this study relative to bladder cancer patients and the use of such antioxidants.

A. The study by Bjelakovic and colleagues represents an analysis of 68 randomized trials based on a search of published studies. When they analyzed 47 low-bias (i.e. good methodological design) trials, they found an increased risk of mortality in participants taking antioxidant therapy over those receiving a placebo (no intervention). In these trials, ßcarotene, vitamin A, and vitamin E —either singly or in combination with other supplements — significantly increased mortality risk. Notably, vitamin C and selenium had no significant effect on mortality and when all (low- and high-bias risk) trials of antioxidant supplements were pooled together there was no significant effect on mortality from antioxidant intake.

Since this report represents a comprehensive review of the topic, including almost a quarter of a million participants (majority of whom were healthy), the findings have to be considered seriously. Recent estimates suggest that as many as 200 million adults in North America and Europe ingest some form of antioxidant supplement, based partially on reports from observational studies which conclude that  antioxidants improve overall health. The authors put forth several possible explanations for the negative effect of antioxidant supplements on mortality. They suggest that while oxidative stress has a hypothesized role in the pathogenesis of many chronic diseases, it may be the consequence of pathological conditions and that, eliminating free radicals from our body might interfere with essential defensive mechanisms like apoptosis, phagocytosis, and detoxification.

With regard to bladder cancer, the idea that dietary supplements might protect against oxidative stress (and in turn against bladder cancer) is a biologically plausible theory but remains to be proven. While the relative risk of mortality associated with antioxidant supplements containing ß-carotene and vitamins A and E was low, it suggests that such agents should not be used for primary prevention. However, if your doctor advises the use of anti-oxidants (in the form of megadose vitamins) for your bladder cancer, this recommendation is likely based on the study by Lamm and colleagues which suggests that addition of   improve results of BCG therapy. It should also be noted that the supplements studies were synthetic supplements and their ‘harmful effects’ should in no way deter one from ingesting more fruits and  vegetables.

Q. What advice would you give bladder cancer patients in terms of nutrition? Should we be following any special diets?

A. Though there is no incontrovertible proof, numerous studies implicate dietary and nutritional factors in the onset and progression of cancers, including bladder, prostate and kidney cancer. Epidemiological data has linked increased risk of bladder cancer with a high fat diet and even specifically with cholesterol intake. Increased risk of bladder cancer has been associated in isolated studies with soy intake and diets which cause altered urinary pH, while decreased risk of recurrence has been associated with selenium, green tea and garlic.

Many of the dietary factors found to be beneficial in epidemiological studies have benefits beyond that of reducing the risk of cancer, and can be advocated as a general recommendation for good health. People, in general, are more receptive to small discreet changes in their lifestyle and food habits than to sweeping drastic measures and it is in this area where education is important. While there is clear evidence that dietary changes such as decreasing fat intake (in particular, animal fat) and increasing fruit and vegetable intake have protective effect in bladder cancer, most people would rather take a pill i.e. a ‘supplement’. This temptation should be avoided. Similarly, unless data emerge to suggest otherwise, patients should not embark on any ‘special diet’ without consulting with their physician – some such diets have, in fact, been associated with significant adverse events.