Dietary supplements, often containing vitamins, are used to ensure that adequate amounts of nutrients are obtained on a daily basis, if optimal amounts of the nutrients cannot be obtained through a varied diet.
Scientific evidence supporting the benefits of some vitamin supplements is well established for certain health conditions, but others need further study. In some cases, vitamin supplements may have unwanted effects, especially if taken before surgery, with other dietary supplements or medicines, or if the person taking them has certain health conditions. Dietary supplements may also contain levels of vitamins many times higher, and in different forms, than one may ingest through food.
There have been mixed studies on the importance and safety of dietary supplementation. A meta-analysis published in 2006 suggested that Vitamin A and E supplements not only provide no tangible health benefits for generally healthy individuals but may really increase mortality, although two large studies included in the analysis involved smokers, for which it was already known that beta-carotene supplements can be harmful. Another study published in May 2009 found that antioxidants such as vitamins C and E may really curb some benefits of exercise. While others findings suggest that evidence of Vitamin E toxicity is limited to specific form taken in excess.
