Vitamin Supplements to Suppress Cancer?

TASK FORCE FINDS LITTLE EVIDENCE TO SUPPORT USE OF VITAMIN

SUPPLEMENTS TO PREVENT CANCER OR HEART DISEASE

The U.S. Preventive Services Task Force today concluded there was insufficient scientific evidence to recommend vitamin supplements as a way to prevent cancer or heart disease and recommended against the use of beta carotene supplements in smokers because of a possible increased risk of lung cancer and death. The Task Force conclusions are based on a review of studies on the use of vitamins A, C, or E, multivitamins with folic acid, or antioxidant combinations to reduce the risk for cancer or cardiovascular disease in adults. These findings are published in the July 1 issue of the Annals of Internal Medicine.

The Task Force is the leading independent panel of private-sector experts in prevention and primary care and is sponsored by the Agency for Healthcare Research and Quality. This marks the first time the Task Force has reviewed studies on the effect of vitamins to reduce cancer and cardiovascular disease.

The Task Force reviewed the results of four clinical trials that found that taking beta carotene did not decrease the risk for lung, prostate, colon, breast, or non-melanoma skin cancer in middle-aged and older adults. Two of these clinical trials found that individuals who take beta carotene and smoke have an increased risk of lung cancer and death.

The Task Force also reviewed both randomized trials and observational studies to determine whether taking vitamins A, C, or E, multivitamins with folic acid, or antioxidant combinations reduced risk of heart disease, stroke or various cancers. The best studies suggested no clear benefit of taking vitamins, but the number and length of the studies was insufficient to rule out possible benefits of long-term vitamin use. Although some of the observational studies suggested possible benefits for some cancers, the Task Force could not determine whether these benefits were due to vitamins or to healthier lifestyles in people who take vitamins. They also did not review evidence on the use of vitamins for patients with known nutritional deficiencies, pregnant and lactating women, children, the elderly, and people with chronic illness. Vitamins may be more appropriate for people in these groups, and the Task Force urges those patients to talk with their clinicians about the potential benefits and harms of using vitamins.

"Vitamin supplements may be necessary for individuals whose diets don't provide the recommended amounts of specific vitamins and especially important for pregnant and nursing women and people with specific illnesses. However, the benefits of vitamin supplements for the general population remain uncertain," said Janet Allan, Ph.D, R.N., vice chair of the Task Force. "There are currently a number of important studies underway which might help answer this important question."

Although most studies reviewed by the Task Force showed that taking vitamins according to the Recommended Daily Allowance does not cause harm, several adverse effects can be caused by taking moderate doses and/or excessive doses of certain vitamins. For example, moderate doses of vitamin A may reduce bone mineral density, and high doses may cause liver damage or in pregnant women, harm to a fetus. The Task Force recommends that patients who take vitamins not take more than the Recommended Daily Allowance and talk to their clinician about the effects vitamins may have on their health.

The Task Force conducts rigorous, impartial assessments of all the scientific evidence for a broad range of preventive services. Its recommendations are considered the gold standard for clinical preventive services. The Task Force based its conclusion on a report from a team led by Cynthia Morris, Ph.D., M.P.H., and Cheryl Ritenbaugh, Ph.D, M.P.H., from AHRQ's Evidence-based Practice Center at Oregon Health & Science University in Portland.

The Task Force grades the strength of the evidence from "A" (strongly recommends), "B" (recommends), "C" (no recommendation for or against), "D" (recommends against) or "I" (insufficient evidence to recommend for or against screening). The Task Force recommends against the use of beta carotene supplements, either alone or in combination, for the prevention of cancer or cardiovascular disease (a "D" recommendation). The Task Force found insufficient evidence to recommend for or against the use of supplements of vitamins A, C, or E, multivitamins with folic acid, or antioxidant combinations for the prevention of cancer or cardiovascular disease (an "I" recommendation).

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