Benefits of Vitamin Supplements Unclear

New research shows there is not enough evidence to confirm vitamin supplements can prevent cancer, heart disease or stroke. In fact, researchers found consuming too much of a particular vitamin may increase a person’s risk of developing disease.
The U.S. Preventive Services Task Force reviewed the results of four clinical studies, which show consuming certain vitamins decreases a person’s chance of developing cancer or cardiovascular disease.

Upon examining the data, researchers found no clear benefits result from vitamin supplement use. However, the length of the study made it impossible to examine the long-term effects of taking vitamins. Although some of the data studied suggested vitamins pose possible benefits for some cancers, the Task Force could not determine if the benefits were due to vitamins or healthier lifestyles in those taking the vitamins.

Although researchers agreed taking vitamins according to the recommended daily allowance does not cause harm, they found several adverse effects can occur if vitamins are taken in large doses. For example, researchers say moderate doses of vitamin A can reduce bone mineral density, and high doses may cause liver damage or harm a fetus.

The Task Force does not recommend using beta-carotene supplements, either alone or in a multivitamin to prevent cancer or cardiovascular disease, giving the vitamin a "D" rating. They also say there is insufficient evidence to recommend using supplements with vitamins A, C or E and multivitamins with folic acid or antioxidant combinations for the prevention of disease.

Researchers say "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 in the general population remain uncertain."