Glucosamine is a combination of an amino acid and a simple sugar, known as an amino monosaccharide.The body synthesizes glucosamine at a rate of four to 20 grams a day, with an average of 12. Its supplemental form is derived from chitin, the exoskeleton, or shells, of marine invertebrates. Chitosan, a popular supplement often included in fat-loss products, is derived from the same source.
Glucosamine is available in several supplemental forms, such as glucosamine hydrochloride, glucosamine sulfate and N-acetyl-glucosamine. The most studied and popular of the three forms is the sulfate.
The purpose of glucosamine supplementation is to prevent and treat joint and connective-tissue problems, including arthritis. Glucosamine is a base element of glycosaminoglycans (GAG), which in turn forms the basic structure of connective tissue, ligaments, skin, tendons and cartilage. Unlike common over-the-counter drugs, such as nonsteroidal anti-inflammatories, which mask pain but do not help regenerate joints or connective tissue, glucosamine may help heal damaged tissue because it provides the raw material for the body's synthesis of GAG.
Animal- and human-based studies show that glucosamine is highly absorbable, averaging 90 percent with oral doses. But as is the case with everything you take orally, glucosamine is processed in the liver before it enters the blood, degrading much of it. Studies show that oral glucosamine has only 26 percent of the bioavailability its intravenously administered counterpart has. Still, enough of the substance survives to peak in the blood eight hours after an oral dose. Studies using radioactively tagged glucosamine show that it takes a direct route to cartilage and connective tissue.
Although those with allergies to shellfish should avoid glucosamine supplements, it's safe for everyone else. Even so, some warnings have been voiced concerning a possible glucosamine-induced interference with glucose and insulin metabolism. A closer look at the studies those warnings came from reveals that, as Shakespeare might have said, 'It's much ado about nothing.'
Animal-based toxicity studies show that glucosamine doses as large as 15,000 milligrams per kilogram (2.2 pounds) are well tolerated with no apparent toxic effects. Such studies have included rats, mice, rabbits, dogs and horses as subjects, and some proved that parenteral administration, or injection, led to possible negative effects on glucose metabolism. The doses used in those studies, though'about 9,035 milligrams per kilogram of bodyweight'aren't comparable to any suggested dose for humans. An oral dose of glucosamine reaches only 20 percent of injection levels, and the suggested oral dose of glucosamine for human use is 23.1 milligrams per kilogram of bodyweight, or 0.25 percent of the amount that made trouble for glucose metabolism. Even huge oral doses of glucosamine'as much as 2,149 milligrams per kilogram of bodyweight'have not been found to affect glucose metabolism in animal subjects.
Other research pointing to possible toxic effects of glucosamine involved isolated-cell, or in vitro, protocols. The doses used in those studies averaged 100 to 200 times higher than blood serum levels expected with oral use of glucosamine. Glucosamine exerts no mutagenic, or cancer-promoting, effects in cells. That's significant because the huge doses used in isolated-cell studies often damage cellular DNA, which is a cause of cell mutations that result in cancer.
In some studies glucosamine was infused in human subjects, and they experienced no negative effects of either insulin or glucose metabolism. That's important because infusions, like injections, bypass liver metabolism, resulting in far higher concentrations of the substance in the blood than you get with an oral dose. The odds that glucosamine will adversely affect either insulin or glucose metabolism are remote at best. A recent review of glucosamine safety and efficiency found that the tolerable daily dose of glucosamine was 184 milligrams per kilogram of bodyweight.1 That amounts to 16,560 milligrams a day in a 200-pound man. In contrast, the usual suggested daily oral dose of glucosamine is 1,500 milligrams, or 23.1 milligrams per kilogram of bodyweight.
Studies comparing glucosamine supplementation to various over-the-counter or prescription pain relievers found that pain reduction was comparable between the drugs and glucosamine. The drugs, however, are considerably more hazardous. Statistics show that more than 16,000 people die yearly directly as a result of using prescription pain relievers for joint pain. That's particularly noteworthy in light of the recent controversy involving a class of prescription drugs known as COX-2 inhibitors. Such drugs are now associated with serious cardiovascular complications in some people, a scenario that doesn't exist with natural remedies like glucosamine. IM
1 Anderson, J.W., et al. (2005). Glucosamine effects in humans: a review of effects on glucose metabolism, side effects, safety considerations and efficacy. Food Chem Toxicol. 43:187-201.