Fact Check: Breast Cancer and Nutritional Supplements

Can nutritional supplements play a role in breast cancer prevention and treatment? Wilmot Cancer Institute researcher Luke Peppone, Ph.D., MPH, studies the use of nutritional supplements and exercise to treat the symptoms and side effects of cancer and its treatments. 

All nutritional supplements should be treated as drugs, he says. People who have cancer should not make assumptions or take advice from family, friends or the Internet about what supplements are best for their particular symptoms. (The same holds true for some foods. For example, if you are drinking grapefruit juice daily, be sure to speak to your doctor about possible drug interactions.)

Integrative medicine is meant to be used in conjunction with standard medical treatment, not in place of medical treatment.

Here, Peppone shares some insights about commonly recommended supplements:

Vitamin D: Studies show that many women have low levels of this essential vitamin, which may contribute to decreased bone mass, joint pain, and a higher risk of fractures. Some hormonal therapies for breast cancer also accelerate bone loss or cause joint pain. Knowing what dose to take, however, is tricky. Individuals absorb vitamin D at different rates, and some people are also getting the vitamin from the sun and fortified foods such as milk and cereal. All women with breast cancer should have a proper blood test to establish a baseline level, and then talk with their doctor about an appropriate dose of vitamin D. Women with ultra-low levels may need some very large doses initially, followed by daily supplementation. Short-term doses of up to 10,000 IUs daily have been shown to be safe for cancer patients. We are currently studying whether high-dose vitamin D is better than standard vitamin D supplementation for bone health in breast cancer patients.

Fish, fish oil, omega 3: These have anti-inflammatory properties that lower triglycerides and help with brain function, eyesight, and heart health — all of which are important for cancer survivors. However, our recent study revealed a surprising outcome, showing that omega 6 supplements (soybean oil), which are usually viewed as far less healthy, actually had a greater impact on reducing breast cancer patients’ extreme fatigue than omega 3 supplements. The study of 108 women was presented at two large meetings for oncologists, and drew attention because the women who took the highest doses of fish oil reported the most fatigue. Plans for a follow-up study are under way. 

An important note about omega 6: Many women with breast cancer shy away from taking any soy because it’s known to contain phytoestrogens, which mimic human estrogen and therefore may be detrimental for women with estrogen-fueled breast cancer. (The research on this is not conclusive.) But phytoestrogens come from protein sources of soy — tofu, soy beans and nuts, soy isolate, etc.—and they are not present in plant-based pure soybean oil, which is the primary ingredient in many bottled salad dressings and is usually sold as “vegetable oil.”

Magnesium: This supplement is popular for calming hot flashes. Studies show that 400-800 mg daily helps to reduce flashes in some women, but will not wipe them out entirely. Side effects include minor gastrointestinal upset in some users.