Even if you aren't a cancer patient, you should tell your healthcare provider about any supplements you're taking. And recognize that more is not necessarily better when it comes to using vitamins and minerals for disease prevention. "We don't know whether going above the baseline helps," says Cohen.
Realize that what's good for someone else may not be good for you. It's important to know that supplements can reduce the effectiveness of certain treatments or make them more toxic—and that what worked for your friend with breast cancer may not work for you. Block does recommend supplements for his patients but tailors them to their circumstances. Those may include the type of cancer—whether a breast cancer is estrogen receptor positive or negative, for example—treatment regimen, specific symptoms, and other conditions in the body. Other doctors say they'll also recommend certain supplements, namely omega-3 fatty acids, calcium, and vitamin D, but their advice, too, will ultimately be individualized.
Eat a balanced, healthful diet. While the role of diet in cancer prevention or in preventing recurrence isn't clear, there's no downside to following the eating patterns (including the Mediterranean diet) associated with better health outcomes and lower body weight. That means eating lots of fruits and vegetables, fish, legumes, and whole grains and avoiding heavily processed, nutritionally empty foods. "Many of the things we take in supplements are found in food," says Donald Abrams, director of the integrative oncology research program at the University of California-San Francisco. And the naturally occurring levels of those nutrients are not likely to be harmful.
An earlier version of this article misstated Peter Gann's title. He is director of the division of pathology research, not director of pathology.