About 38% of adults in the United States and nearly 12% of children use some form of complementary and alternative medicine (CAM), according to a new government survey. Overall CAM use among adults has remained relatively steady since a similar survey in 2002. However, there were significant increases in some types, such as deep breathing, meditation, massage therapy and yoga.

CAM is a group of diverse medical and health care systems, practices and products that are not generally considered to be part of conventional medicine. The 2007 survey results are based on data from more than 23,300 interviews with American adults and more than 9,400 interviews with adults on behalf of a child in their household. The survey included questions on 36 types of commonly used CAM therapies.

The most common uses of CAM in adults are for back and neck pain, joint pain, arthritis, anxiety, cholesterol, head or chest colds and other musculoskeletal conditions.

“The data point out the need for patients and health care providers to openly discuss CAM use to ensure safe and coordinated care,” said Dr. Josephine P. Briggs, director of NIH’s National Center for Complementary and Alternative Medicine.

Two large-scale clinical trials found that vitamin E, vitamin C or selenium supplements don’t reduce the risk of prostate cancer or other cancers in older men.

Previous studies had suggested that vitamin E or selenium supplements might reduce prostate cancer risk. Smaller studies also hinted that vitamin C might help to prevent prostate and other cancers.

NIH-funded researchers tested how prostate cancer and total cancer risk is affected by the dietary supplements. One research group recruited more than 35,000 men, age 50 and older, who had no evidence of prostate cancer. The men were randomly assigned to receive selenium, vitamin E, both or inactive placebo pills.

The study was cut short in late 2008, after an average follow-up of about 5.5 years. That’s because the supplements seemed to offer no cancer-related benefits.

The second trial looked at vitamin E and C supplements. More than 14,000 male doctors, age 50 or older, were randomly assigned to take either vitamin E, vitamin C, both or a placebo. After an average follow-up of about 8 years, neither vitamin—alone or in combination—significantly reduced the risk of prostate or other cancers compared to the placebo group.

Dietary supplements can often seem beneficial in small studies. The new studies highlight the fact that large, carefully controlled trials are needed to test whether they really live up to their hoped-for benefits.