The U.S. Preventive Services Task Force has concluded that there is insufficient scientific evidence to recommend vitamin supplements as a way to prevent cancer or heart disease. In addition, the Task Force has 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, which is the leading independent panel of private-sector experts in prevention and primary care, 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 which 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 were 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.
The Task Force 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 patients in these groups to talk with their clinicians about the potential benefits and harms of using vitamins.
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 that the patients talk with their clinicians 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. Task Force recommendations are considered the gold standard for clinical preventive services. The Task Force based its conclusions 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).
Select for vitamin supplementation recommendations and materials for clinicians.
The findings also are published in "Routine vitamin supplementation to prevent cancer and cardiovascular disease: Recommendations and rationale," in the July 1, 2003, Annals of Internal Medicine 139(1), pp. 51-55.
Previous Task Force recommendations, summaries of the evidence, easy-to-read fact sheets explaining the recommendations, and related materials are available from the AHRQ Publications Clearinghouse.
Clinical information is also available from the National Guideline Clearinghouse™.