Commonly derived from shrimp shells, glucosamine is a form of sugar that occurs naturally in the body. As well as relieving the joint pain, it is also believed to increase flexibility in joints and may stimulate the regrowth of cartilage, thereby helping to stave off more problems in the future.
It is usually administered in supplements in the form of glucosamine chloride or glucosamine sulphate, and may also be combined with chondroitin sulphate.
Since the withdrawal of Cox-2 inhibitor drugs such as Vioxx last year, there has been an upsurge of interest in natural substances to relieve joint pain. According to Mintel's Global New Products Database, glucosamine was contained in 48 percent of all joint health supplements launched in the US in the last five years.
Osteoarthritris affects between six and 12 percent of the adult population in the United States, and up to a third of people over the age of 65.
The researchers from Tufts New England Medical Center did not question the efficacy of glucosamine per se, as this has been borne out by in vitro studies. But they did draw attention to some contradiction in the results from human studies using commercially available supplements: while industry-sponsored randomized clinical controlled trials have indicated "moderate efficacy", some independent investigations have yielded negative results.
This, they say, "invites skepticism". It led them to seek to find out whether the most commonly consumed doses were high enough to have any real impact. Before reaching peripheral circulation, glucosamine must first pass through the liver, during which some of the benefit may be lost.
The study, published online in the Annals of Rheumatic Disease involved 18 osteoarthritis sufferers, who took 1500mg of commercially-available glucosamine sulphate after an overnight fast.
Their serum glucosamine levels were measured through blood tests at baseline and every 15 to 30 minutes over the next three hours, using a new method that enabled the detection of levels as low as 0.5 micromoles at 1:10 serum dilution.
In 17 of the 18 subjects, serum glucosamine levels began to rise 30 to 45 minutes after ingestion and reached a peak 90 to 180 minutes after ingestion. The maximum detected level was 11.5 micromoles.
The researchers noted that most in vitro experiments investigating the efficacy of glucosamine use concentrations in excess of 100 micromoles - almost ten times higher than those seen in this study.
"This raises questions regarding current biologic rationales for glucosamine usage that were based on in vitro effects of glucosamine at much higher concentrations," wrote the researchers.
However it is not advised that consumers up their dose of glucosamine supplements, since the effects of larger doses are currently being investigated. Since glucosamine is a sugar, there is some concern that increasing the doses may also increase the risk of developing diabetes.