Before you take any supplements for disease prevention, it's important to know whether the potential benefits outweigh the risks. To make that conclusion, you need to look at the results of well-designed studies. A recent randomized trial in men suggested multivitamins have possible benefits for cancer prevention. For many of the other popular supplements, including vitamin D and omega-3 fatty acids, results from randomized controlled trials should be available within the next five years, according to Dr. Manson.
Proteins are chains of amino acids. Nine of these proteinogenic amino acids are considered essential for humans because they cannot be produced from other compounds by the human body and so must be taken in as food. Recommended intakes, expressed as milligrams per kilogram of body weight per day, have been established.[26] Other amino acids may be conditionally essential for certain ages or medical conditions. Amino acids, individually and in combinations, are sold as dietary supplements. The claim for supplementing with the branched chain amino acids leucine, valine and isoleucine is for stimulating muscle protein synthesis. A review of the literature concluded this claim was unwarranted.[36] In elderly people, supplementation with just leucine resulted in a modest (0.99 kg) increase in lean body mass.[37] The non-essential amino acid arginine, consumed in sufficient amounts, is thought to act as a donor for the synthesis of nitric oxide, a vasodilator. A review confirmed blood pressure lowering.[38] Taurine, a popular dietary supplement ingredient with claims made for sports performance, is technically not an amino acid. It is synthesized in the body from the amino acid cysteine.[39]
^ Dwyer, J. T; Wiemer, K. L; Dary, O; Keen, C. L; King, J. C; Miller, K. B; Philbert, M. A; Tarasuk, V; Taylor, C. L; Gaine, P. C; Jarvis, A. B; Bailey, R. L (2015). "Fortification and Health: Challenges and Opportunities". Advances in Nutrition: An International Review Journal. 6 (1): 124–131. doi:10.3945/an.114.007443. PMC 4288271. PMID 25593151.
Dietary supplements are complex products. The FDA has established good manufacturing practices (GMPs) for dietary supplements to help ensure their identity, purity, strength, and composition. These GMPs are designed to prevent the inclusion of the wrong ingredient, the addition of too much or too little of an ingredient, the possibility of contamination, and the improper packaging and labeling of a product. The FDA periodically inspects facilities that manufacture dietary supplements.