MONDAY, Feb. 24, 2014 (HealthDay News) -- Healthy Americans shouldn't take vitamin E or beta carotene supplements to help prevent heart disease or cancer, an influential government panel of experts concludes. The same group said the value of a daily multivitamin for dodging these diseases remains unclear.

In its statement released Monday, the U.S. Preventive Services Task Force added that taking beta carotene might even raise health risks for some people.

Ample evidence now shows vitamin E doesn't do anything to prevent heart disease or cancer, while beta carotene also doesn't work and may increase the risk of lung cancer in people who are already at higher risk for the disease, the task force noted.

"Unfortunately, at this point in time, the science is not sufficient for us to estimate either how much benefit or harm there is from taking multivitamin supplements for cancer or heart disease," said Dr. Michael LeFevre, co-vice chair of the task force.

Heart disease and cancer are leading causes of death in the United States. About half of adults in this country take daily supplements, according to the U.S. Centers for Disease Control and Prevention, although there's little proof that they do anything to keep people healthy.

To try to give Americans better guidance, the 16-member panel took an in-depth look at studies conducted over the past 10 years on vitamins.

They reviewed five studies on multivitamins and 24 studies on individual or paired supplements.

Three of the five studies on multivitamins found no benefit in taking them. But two large studies, one conducted in the United States and one in France, suggested that taking a daily multivitamin might slightly reduce the risk of cancer in older men. One study didn't include women. The other found no effect in women.

The picture was even murkier for studies of single supplements or supplement pairs. Only a few studies were available for each supplement, and the doses given to people varied a lot from study to study, making it tough to draw broad conclusions, the panel said.

Vitamin E and beta carotene were unique. Out of six randomized controlled trials -- the kind of studies that produce the strongest evidence -- none found significant benefits of vitamin E against heart disease or cancer, leading the task force to recommend against its use. Another six clinical trials of beta carotene found no benefit, and two found proof of harm. On average, extra beta carotene increased the risk of lung cancer in smokers by about 24 percent, the panel said.

The new statement, published online Feb. 24 in the Annals of Internal Medicine, is an update of a 2003 recommendation. Experts say very little has changed over the last decade.

"It's disappointing," said LeFevre. "But we still can't answer the question."

Representatives of the vitamin industry said the task force's recommendations were very specific: They only apply to healthy adults over age 50, and they aren't relevant to children, women of childbearing age or adults with known nutritional deficiencies.

And the representatives added the report really isn't a reason to stop taking most supplements.

"It's very different to say insufficient evidence. It doesn't mean we've got firm evidence that things don't work," said Duffy MacKay, vice president of scientific and regulatory affairs for the Council for Responsible Nutrition.

But an expert not involved in drafting the recommendations said the report proves that supplements are no substitute for eating a healthy diet and controlling body weight.

"The current U.S. Preventive Services Task Force report has collated the available data and confirmed what many of us have suspected -- popping a pill is no substitute for eating sensibly and moving more," said Alice Lichtenstein, a professor of nutrition science and policy at Tufts University in Boston.

The American Heart Association urges people to get their nutrients from a healthy diet, rather than supplements. The American Cancer Society has said that current evidence doesn't support the use of dietary supplements for cancer prevention.

More information

Visit the U.S. National Institutes of Healthfor more about multivitamins.