Do Nutritional Supplements Help Prevent Cancer?

For many people, the risks may outweigh the benefits
Forty-five percent of American men and 55% of American women take nutritional supplements to prevent cancer and other serious health conditions. While some supplements have proven to be effective treatments for some medical conditions, the benefits of others are not scientifically proven, and a few have actually been proven dangerous when taken in excess.

The U.S. Food and Drug Administration (FDA) categorizes nutritional supplements under the general umbrella of foods rather than drugs. Unlike drugs, which cannot be marketed until they have passed clinical trials and a rigorous approval process, foods and nutritional supplements cannot be removed from the market by the FDA unless they are proven to be dangerous or have false label information. Although supplement manufacturers are required to list all active ingredients on their products’ labels and follow FDA manufacturing guidelines, the supplements do not have to be proven safe or effective.

Possible dangers

Because Americans tend to get enough of most vitamins in their normal diet, taking extra vitamins can cause an overdose; in 2008, more than 69,000 cases of toxicity due to a vitamin overdose were reported.

For example, taking more than 7.5 mg/day of vitamin A can lead to headaches, irritability, anoxia (lack of oxygen to the tissues), dry or cracked skin, and osteoporosis (reduced bone density). This harmful dose is available over the counter in many stores.

Another danger of supplements is that some can interact with some medicines in ways that harm the patient. People taking prescription medications should inform their health care team about any nutritional supplements they are taking.

In some studies, certain vitamins have also been associated with promoting cancer. One trial of selenium for the prevention of prostate, lung, or colon cancer recurrence was stopped because men who took 200 μg of selenium per day (12 times the recommended dose) had a higher recurrence rate than patients who did not take the supplement.

The vitamin D debate

Vitamin D and its effects on cancer have recently received a lot of attention in the media, but scientists have not reached a consensus about the effectiveness of vitamin D supplements for preventing cancer.

In a study currently under way, thousands of healthy men and women who take vitamin D and/or fish oil supplements will be examined at regular intervals for 5 years to determine the benefits of these supplements for preventing cancer and cardiovascular disease. Secondary goals of the study are to observe whether the supplements affect cognitive problems, diabetes, hypertension (high blood pressure), autoimmune disorders, bone fractures, mood disorders, or infections.

Nutrients in foods

An apple a day may really keep the doctor away. Fruits and vegetables contain important nutrients and fiber, which helps protect against colon cancer.

Studies have shown that eating fresh fruits and vegetables also reduces both the risk and recurrence rate of breast cancer. For example, women with BRCA1 gene mutations have a lifetime breast cancer risk around 60%, but one study found that the risk dropped to less than 30% when these women included a large variety of produce in their regular diet.

Another study showed that women who regularly ate mushrooms had a breast cancer risk about two-thirds lower than those who did not, and those whose daily diet included both mushrooms and green tea had an even lower breast cancer risk.

In 2010, the American Institute for Cancer Research estimated that a third of the cancers that occur every year in the United States could be prevented by lifestyle changes, including eating more whole foods.

The reason whole foods are more beneficial than vitamin supplements is probably that whole foods contain many nutrients that work synergistically to protect against cancer. Salmon, for example, is superior to salmon oil supplements because although both provide fatty acids, salmon provides nutrients not found in oils, such as vitamins D and B, amino acids, calcium, and selenium.

Foods known or believed to help prevent cancer include:

all berries grapes tomatoes mushrooms green tea salmon squash

broccoli cauliflower cabbage brussels sprouts linseed flaxseed

Physicians sometimes prescribe supplements to treat certain medical conditions, but for most people, a diet that includes healthful foods can eliminate the need for supplements. Bon appétit!

– J. Delsigne

For more information, talk to your physician, visit www.mdanderson.org, or call askMDAnderson at 877-632-6789. If you are a current MD Anderson patient and would like to consult a registered dietician, call 713-563-5167.