Glucosamine

Glucosamine is an amino monosaccharide that serves as a fundamental building block for glycosaminoglycans (GAGs) and proteoglycans, the molecules that provide cartilage with its shock-absorbing and lubricating properties. The body synthesizes glucosamine from glucose and glutamine, but production declines with age, contributing to cartilage degradation. Supplemental glucosamine—primarily as the sulfate salt—has been extensively studied in osteoarthritis, with the European GUIDE trial and Reginster's 3-year RCT showing significant reductions in joint space narrowing and symptom scores compared to placebo. The sulfate form is generally preferred over the hydrochloride form, as the sulfate moiety itself supports GAG synthesis. Glucosamine is often combined with chondroitin sulfate for additive joint-protective effects.