Vitamins, minerals, herbs, and extracts—the range of bottles on display in the supplement aisle is mind-boggling. Even more confusing are the claims they make, everything from battling fatigue to boosting immunity. Do any of them help against cancer?
The fact is, researchers don’t yet know. Many supplements touted as cancer fighters haven’t been tested. Those that have been studied haven’t proved to be reliably effective. What’s more, there’s growing evidence that some substances sold in dietary supplements may be hazardous for people undergoing cancer treatment.
Green tea, for instance, a popular herbal remedy, has been shown to block cancer in animal studies. Certain forms of cancer are less common in cultures where green tea is consumed regularly—indirect evidence that it may help lower risk. Supplement aisles now stock pills with concentrated forms of green tea. But in 2009, researchers at the University of Southern California Keck School of Medicine in Los Angeles, published a report showing that polyphenols in green tea block the effectiveness of a drug called bortezomib, which is widely used in patients with multiple myeloma.
Fish oil pills are another popular supplement that may combine benefits and risks. The omega-3 fatty acids they contain have been shown to lower heart disease risk and may also reduce the risk of certain cancers, including colon cancer. Preliminary findings suggest that fish oil supplements may improve immune function in patients with colon cancer. But there’s also worrisome evidence that links some types of fish oil to greater risk of prostate cancer.
By far the fiercest controversy currently swirls around the issue of antioxidant vitamins. For years, researchers have theorized that these compounds, by blocking damage done by free radicals, may protect cells from turning cancerous. There’s solid evidence that people who eat a diet rich in fruits and vegetables abundant in antioxidants are protected against cancer. Many people with cancer pop antioxidant supplements. But alarming results from the Supplementation in Vitamins and Mineral Antioxidants study found that melanoma risk was four times higher in women who received an antioxidant supplement. A review of data from 68 trials, published in the Journal of the American Medical Association in 2007, found that some antioxidant supplements—including beta carotene, vitamin A, and vitamin E—were associated with increased risk of death.
There may be other reasons to be cautious about antioxidants.
A controversial report in the Journal of the National Cancer Institute published in 2008 warned that antioxidant supplements may actually protect cancer cells from attack by chemotherapy drugs or radiation therapy. The authors, who represented experts in a wide range of cancers, recommend that patients undergoing chemotherapy or radiation be advised not to take antioxidant pills.
Much more needs to be learned about potential benefits and risks, most experts agree. One thing is clear: dietary supplements have both benefits and unwanted side effects. Before you take them, it’s wise to talk to your doctor—especially if you’re being treated for cancer.
Peter Jaret is a freelance writer in Petaluma, Calif.