Osteoarthritis results from progressive catabolic loss of cartilage proteoglycans, owing to an imbalance between synthesis and degradation. Standard drug therapy is only of palliative benefit and may exacerbate loss of cartilage. Glucosamine is an intermediate in mucopolysaccharide synthesis, and its availability in cartilage tissue culture can be rate-limiting for proteoglycan production. A number of double-blind studies dating from the early 1980s demonstrate that oral glucosamine decreases pain and improves mobility in osteoarthritis, without side effects. Nevertheless, medical researchers and physicians in the US have totally ignored this rational and safe therapeutic strategy. By mechanisms that are still unclear, the natural methyl donor S-adenosylmethionine also promotes production of cartilage proteoglycans, and is therapeutically beneficial in osteoarthritis in well-tolerated oral doses. These and other safe nutritional measures supporting proteoglycan synthesis, may offer a practical means of preventing or postponing the onset of osteoarthritis in older people or athletes.