Glucosamine

Glucosamine is a substance that occurs naturally in the human body, primarily in cartilage, synovial fluid, and certain tissues. It is a so-called aminoglucose: a compound that contains both a sugar and an amino acid component.

In many cases, glucosamine is extracted from the shells of crustaceans such as shrimp or crabs. Nowadays, plant-based and fully synthetic versions are also used as alternatives.

In supplement form, glucosamine usually comes in three different varieties:

• Glucosamine sulfate 
• Glucosamine hydrochloride 
• N-acetylglucosamine 

The difference lies primarily in the chemical structure and stability. For example, glucosamine sulfate is often bound to sodium or potassium for stability, while glucosamine hydrochloride is bound to hydrochloric acid. N-acetylglucosamine is a separate derivative with a slightly different structure.

No, these are two different substances. Glucosamine is an aminoglucose, while chondroitin is a glycosaminoglycan. They're often mentioned interchangeably, but chemically they're not the same.

Studies show that glucosamine has shown beneficial results. For example, a study published inThe Lancet (Reginster et al., 2001), 212 adults with knee osteoarthritis for three years. Participants who received glucosamine sulfate daily showed less joint space narrowing on average than the placebo group.

In another three-year study with 202 participants, published in Archives of Internal Medicine (Pavelká et al., 2002), one group received glucosamine sulfate daily and the other a placebo. Using x-rays, the researchers observed that the space between the bones in the knee joint, which normally narrows with osteoarthritis, remained virtually unchanged in the glucosamine group, while it decreased in the placebo group. In other words, the decline was slower in the people who received glucosamine.

Sources: 

Reginster, JY, Deroisy, R., Rovati, LC, et al. (2001).Long-term effects of glucosamine sulphate on osteoarthritis progression: a randomized, placebo-controlled clinical trial. The Lancet, 357(9252), 251–256.https://doi.org/10.1016/S0140-6736(00)03610-2 

Source:Pavelká, K., et al. (2002).Glucosamine sulfate use and delay of progression of knee osteoarthritis: a 3-year, randomized, placebo-controlled, double-blind study. Archives of Internal Medicine, 162(18), 2113–2123.https://doi.org/10.1001/archinte.162.18.2113