Approximately one third of adults in the United States take dietary supplements. Many of these people take supplements to ensure adequate nutrition and to prevent or treat disease. Huang and colleagues analyzed the literature on the effectiveness of multivitamin and mineral supplements in the general population for the primary prevention of cancer and chronic disease as well as the safety of these supplements in adults and children. The Agency for Healthcare Research and Quality was contracted to study these questions.
A multivitamin and mineral supplement was defined as containing three or more vitamins or minerals without herbs, hormones, or drugs. For the literature search, the authors included randomized controlled trials (RCTs) on the effectiveness of these supplements and also looked at observational studies and RCTs on the safety of these supplements. They found five trials, one each on the effectiveness of multivitamin and mineral supplements for the prevention of cancer, cardiovascular disease, hypertension, cataracts, and age-related macular degeneration; however, no RCTs on other chronic diseases were found. The overall study quality was fair. Most studies followed patients for five years or more.
For the primary prevention of cancer, cardiovascular disease, cataracts, age-related macular degeneration, and hypertension, the authors found that the strength of the evidence supporting the effectiveness of multivitamin and mineral supplements was very low. However, it was suggested that supplementation may slow the progression of age-related macular degeneration in patients who are at a higher risk of the disease’s advanced stages. Four trials and three case reports were found that addressed the safety of multivitamin and mineral supplementation, but there was not a consistent pattern of increased adverse events.
The authors conclude that it is not clear if multivitamin and mineral supplementation is efficacious for primary prevention of hypertension, cardiovascular disease, or cataracts in the general population. There also are no data comparing a healthful, balanced diet to dietary supplementation. Although it is unlikely that there are serious adverse effects from multivitamin and mineral supplementation, physicians should be aware that there are few data to ensure the safety of their patients.