MSM is promoted as a natural source of sulfur by the supplement and health food industry, suggesting that people are deficient in sulfur intake. However, protein in the diet is an abundant source of sulfur, which is contained in the amino acids methionine and cysteine. MSM is sold as a dietary supplement that is marketed with a variety of claims and is commonly used (often in combination with glucosamine and/or chondroitin) for helping to treat or prevent osteoarthritis. U.S. Retail sales of MSM as a single ingredient in dietary supplements amounted to $115 million in 2003. The biochemical effects of supplemental methylsulfonylmethane are poorly understood. Some researchers have suggested that MSM has anti-inflammatory effects. Any health effects of dimethyl sulfoxide (DMSO) may be mediated, at least in part, by MSM. Stanley W. Jacob, M.D., of the Oregon Health and Science University, claims to have used MSM to treat over 18,000 patients with a variety of ailments.