In a sign of continued growth in the popularity of complementary and alternative medicine (CAM), a study has found Americans are spending billions on non-conventional medical treatments.

According to the National Center for Complementary and Alternative Medicine of the National Institutes of Health, Americans spent $33.9 billion on CAM in 2007. CAM procedures include herbal supplements, meditation, chiropractic and acupuncture.

Meanwhile, the 2007 National Health Interview Survey has found that approximately 38 percent of adults use some form of CAM for health and wellness or to treat a variety of diseases and conditions.

“With so many Americans using and spending money on CAM therapies, it is extremely important to know whether the products and practices they use are safe and effective,” says Dr. Josephine P. Briggs, director of NCCAM.

“This underscores the importance of conducting rigorous research and providing evidence-based information on CAM so that health care providers and the public can make well-informed decisions,” she adds.

Numerous medical and academic centers throughout the country are already engaged in similar research, and their studies are uncovering new benefits of vitamins, including vitamin D, which can be obtained in the form of nutritional supplements.

Their work has gained even more importance in the face of escalating medical costs and what some see as a dysfunctional U.S. healthcare system which fails to cover some 40 million Americans.