The Agency for Healthcare Research and Quality(AHRQ), through its Evidence-Based Practice Centers(EPCs), sponsors the development of evidence reports and technology assessments to assist public- and private-sector organizations in their efforts to improve the quality of health care in the United States. This report was requested and funded by the Office of Dietary Supplements, National Institutes of Health. The reports and assessments provide organizations with comprehensive, science-based information on common, costly medical conditions and new health care technologies. The EPCs systematically review the relevant scientific literature on topics assigned to them by AHRQ and conduct additional analyses when appropriate prior to developing their reports and assessments.

To bring the broadest range of experts into the development of evidence reports and health technology assessments, AHRQ encourages the EPCs to form partnerships and enter into collaborations with other medical and research organizations. The EPCs work with these partner organizations to ensure that the evidence reports and technology assessments they produce will become building blocks for health care quality improvement projects throughout the Nation. The reports undergo peer review prior to their release.

AHRQ expects that the EPC evidence reports and technology assessments will inform individual health plans, providers, and purchasers as well as the health care system as a whole by providing important information to help improve health care quality.

We welcome comments on this evidence report. They may be sent by mail to the Task Order Officer named below at: Agency for Healthcare Research and Quality, 540 Gaither Road, Rockville, MD 20850, or by email to epc@ahrq.gov.

• Carolyn M Clancy, M.D.
• Director
• Agency for Healthcare Resesarch and Quality

• Paul Coates, Ph.D.
• Director
• Office of Dietary Supplements
• National Institutes of Health

• Jean Slutsky, P.A., M.S.P.H.
• Director
• Center for Outcomes and Evidence
• Agency for Healthcare Research and Quality

• Kenneth S. Fink, M.D., M.G.A., M.P.H.
• Director, EPC Program
• Agency for Healthcare Research and Quality

• Beth A. Collins-Sharp, R.N.,Ph.D.
• EPC Program Task Order Officer
• Agency for Healthcare Research and Quality