Nutritional supplement research is unsatisfactory.
The extraordinary prevalence of dietary supplements spans television ads, books and the Internet, plus the recommendations of well-meaning friends and colleagues. The relentless promotion and claims of profit-seeking marketers contribute to supplement appeal. Cancer patients and survivors are routinely encouraged to consider or try such products, and the great majority do both.
Cancer patients who use dietary supplements must contend with multiple clinically important issues, including the dangers of hiding supplement use from physicians and the opposite—bringing bags of supplement bottles to their oncologists for discussion and guidance—as well as needing control to do whatever possible to improve their health.
The motivation to use supplements is entirely understandable, but the heart of the problem is the lack of good guidance. Available data are inconsistent, contradictory, limited, confusing and often inadequate.
Nutritional supplement research began with epidemiologic diet studies showing statistical associations between nutrients and cancer prevention. Researchers then looked at individual nutrients contained in the good diets. However, selecting a single nutrient from the many in a vegetable, for example, and administering it as a medication, is not a viable follow-up. It is unlikely that a single ingredient by itself produces a benefit. Instead, it is likely that interactions among several, if not all, elements produced the benefits seen in diet studies, but not when studied as an isolated element or two.
The famous study of beta-carotene and people at high risk for lung cancer was based on diet questionnaire results showing that smokers who consumed beta-carotene-rich foods had a reduced risk of lung cancer. But that does not imply that a high dose of a single synthetic derivative will achieve the same cancer preventive advantage. In fact, a subsequent beta-carotene study using a synthetic derivative showed the opposite. The isolated derivative of beta-carotene-rich foods caused more, not fewer, deaths in people at high risk for lung cancer, so the study was halted.
Further, the context of all diet studies must be considered. The beta-carotene study, for example, involved people with a history of smoking or asbestos exposure. It is unlikely that any one vitamin or nutrient could offset the damage that smoking inflicts.
Supplement studies often contradict one another because researchers use different forms of the same nutrient. Vitamin E, for example, is not one chemical substance; there are actually eight forms. One, alpha-tocopherol, has been studied often in cancer. There are also many forms of vitamin D. Moreover, it is uncertain whether the various forms work synergistically. Only future research using complex vitamins can answer this question.
Many claims are based on false, insufficient or poor-quality evidence, heightening the dangers of their use during cancer treatment. There is a very real possibility that antioxidants may interfere with radiation therapy and some chemotherapeutic agents. What patients may gain by taking supplements in short-term feelings of well-being, they may lose in reduced long-term treatment effectiveness. After enduring the difficulties of cancer treatment, it is best to avoid the possibility of minimizing its effectiveness.
Don’t ascribe too much promise to single nutrients. Have realistic expectations, based on the best science available. Get your vitamins from food.
Barrie R. Cassileth, PhD, is chief of Integrative Medicine Service at Memorial Sloan-Kettering Cancer Center in New York City and a member of CURE’s advisory board. Donald Garrity, RD, is an Integrative Medicine Service nutritionist at Memorial Sloan-Kettering.