Dietary supplements are regularly used by at least half of the American population, yet the health benefits of these agents are unclear.

A systematic review to determine the benefits and risks of dietary supplements in Westernized societies. Data Sources: MEDLINE, Embase, Cochrane Register of Controlled Trials and citation review of relevant articles. Study Selection: Randomized, placebo-controlled clinical trials in non-pregnant Westernized adults that evaluated clinical outcomes of nutritional supplements. Data Extraction: Data were abstracted on study design, study size, study setting, patient population, dietary intervention and clinical outcomes. The outcome of each study was classified as non-beneficial, beneficial or harmful according to whether the end-point(s) of interest reached statistical significance.

Data Synthesis: Sixty-three studies met the criteria for our systematic review. No benefit was recorded in 45 studies, with 10 of these showing a trend towards harm and with two showing a trend towards benefit. Four studies reported harm with increased cancer deaths (n=2) and increased fractures (n=2). Two studies reported both a harmful as well as a beneficial outcome.

A beneficial outcome was reported in 12 studies; 6 which studied vitamin D and three which investigated omega-3 fatty acids. While a benefit was reported in one study each which investigated Vitamin E, folic acid and Ginkgo biloba this benefit was not confirmed by larger and more adequately powered studies.

With the possible exceptions of Vitamin D and omega-3 fatty acids there is no data to support the widespread use of dietary supplements in Westernized populations; indeed, many of these supplements may be harmful.