If you are taking vitamin supplements to reduce your risk of heart disease or cancer, a group of health experts want you to know that those vitamins may actually increase your risk of cancer.

    The US Preventive Services Task Force came to this conclusion after reviewing dozens of studies.

    Nearly half of adults in the US take at least one vitamin or mineral supplement on a regular basis. These pills are advertised as a way to promote general health. In some cases, manufacturers promote them as cancer fighters and heart protectors.

    Studies in animals and in laboratory dishes suggest that oxidative(氧化性的) stress contributes to diseases like cancer and heart disease. If so, there is a reason to believe that antioxidants—including beta-carotene, vitamins A, C, and E—could be useful as preventive medicines.

    But when the Task Force examined the medical evidence on vitamins, it found “inadequate(不充分的) evidence” to support the claims that vitamin and mineral supplements benefit healthy adults.

    “Cardiovascular(心血管的) disease and cancer have a significant health impact in America, and we all want to find ways to prevent these diseases,” Dr. Virginia Moyer, who heads the Task Force, said in a statement. But so far, she added, the medical evidence does not show that taking vitamins is helpful in this regard.

    However, the Task Force did find “adequate evidence” that people with a raised risk for lung cancer actually increase their risk further by taking beta-carotene, a precursor of vitamin A.

    The Task Force recommendations of taking vitamins regularly apply to healthy adults aged 50 and older who don't have “special nutritional needs”. The advice does not apply to children, women who are pregnant or may become pregnant, people with chronic illnesses, or people who have to take supplements because they can't get all their essential nutrients from their diet.