N-acetylglucosamine is another member of the group of eight essential sugars. It is best known by its derivative, Glucosamine, which is now a popular natural remedy for osteoarthritis.

Absorption
There are three common commercial forms of Glucosamine: N-acetylglucosamine, hydrochloride, and sulfate. Scientific literature does not support the use of N-acetylglucosamine or the hydrochloride form. Human studies show that Glucosamine sulfate is almost 98% absorbed. It is then distributed in the body primarily to joint tissues where it is incorporated into the connective tissue matrix of cartilage, ligaments and tendons.

Apparently, it is the sulfur component of Glucosamine sulfate that is crucial to its mechanism of action. In fact, N-acetylglucosamine and Glucosamine sulfate are two entirely different molecules. The structural difference is this: N-acetylglucosamine has a portion of an acetic acid molecule attached to it, causing the body to handle the two compounds differently. Glucosamine sulfate absorption appears to be active, whereas no mechanism exists for the absorption of the N-form. It is advisable to use Glucosamine sulfate in conjunction with Chondroitin sulfate, since both enhance the absorption of the other.

There are several reasons why the absorption of N-acetylglucosamine is questionable in humans:

• It is quickly digested by intestinal bacteria.
• It is a known binder of dietary lectins in the gut, with the complex being excreted in the feces rather than being absorbed.
• A large percentage cannot penetrate the cell membranes; and, as a result, it is broken down by intestinal cells and rendered useless to glycoproteins and mucopolysaccharides.

Excretion
Animal studies reveal that Glucosamine is eliminated in the urine. More information is needed to see if the substance is eliminated by other means or if there are alterations in excretion during disease states. According to scientific calculations that are based on animal studies, elimination of this sugar in humans would take 8-12 hours.

Functions
Glucosamine sulfate helps repair cartilage while decreasing pain and inflammation. It also seems to increase the range of motion in osteoarthritis. Injuries to the joints also heal more rapidly when this sugar is added to the diet. There is strong evidence to this supposition. Glucosamine is the substrate for the synthesis of glycosaminoglycan, the important building block of damaged cartilage. It appears that Glucosamine is able to prevent its metabolic breakdown. Rather, it is attracted to and directly involved in the repair of damaged cartilage. Based on these findings, scientists are now speculating that Glucosamine may also help generalized wound repair.

Deficiencies or malfunctions in the ability to metabolize this sugar have been linked to diseases of the bowel and bladder. Glucosamine has been shown to help repair the mucosal-lining defensive barrier called the glycosaminoglycan layer (GAG). Defects in the GAG layer have been implicated in Crohn's disease, Ulcerative Colitis, and Interstitial Cystitis.

Glucosamine is an immune modulator with antitumor and antiviral properties, as well as activity against HIV. Animal studies have shown that Glucosamine prevented the human influenza virus and the herpes virus.

One of the most striking effects of Glucosamine is its ability to reduce the progression of experimental cancers. For instance, the growth of Ehrlich ascites tumors in mice were inhibited simply by adding the essential sugars Mannose and Glucosamine into their drinking water. The survival rate significantly increased while the tumors decreased. Other such tumors produced the same results. Reductions in blood levels of Glucosamine have been found in those with colon cancer. Distribution of the sugar is also altered when other cancerous tissues are present.

As with some of the other essential sugars, scientists are finding that Glucosamine is also vital to learning. Researchers found that after two groups of mice received Glucosamine injections, the group that had been given 15-minutes worth of avoidance-conditioning training in which they were punished by electric shock for responding to some stimuli and rewarded with food for responding to others, incorporated nearly double the amount of Glucosamine into their brains as the mice that were not trained and were kept quietly in a cage.

N-acetylglucosamine concentrations were also found in mammalian brains, suggesting a role in nerve function. This would also tie in with its role in the learning process.

The thyroid gland is known to have N-acetylglucosamine receptors on its surface which are believed to play a role in the transport of thyroglobulin (an iodine-containing glycoprotein) within the gland itself.

Since concentrated amounts are found in several tissues and organs, especially the liver, small intestine, testes, epithelial cells of the endocrine and sebaceous glands, and endothelial cells of blood vessels, it is readily assumed that Glucosamine plays an important role in these areas. Exactly what those roles are is still being researched.

Retinal tissue from human eye donors showed that Glucosamine readily preferred the photoreceptor layer of the retina, suggesting that, not only this sugar is needed for vision, but the others as well since several essential sugar concentrations have been found in the eye structure.

Significant amounts of Glucosamine have been found in the intestinal mucin, which binds chloresterol, thereby limiting its absorption.

Glucosamine has proven to decrease insulin secretion without suppressing liver glucose production. This means that the "signaling" appears to be a normal regulatory role for the sugar in managing utilization.

Safety
There does not appear to be any side effects or safety issues when taking supplemental Glucosamine, although it may delay insulin-mediated glucose uptake in some people. Therefore, diabetics should be cautious when starting out with this sugar. As with all of the essential sugars, dosage should begin with small amounts and work up to levels that are functional for the individual.

Based on information available to date, it appears that 1 gram in a 150-pound healthy adult is a safe maximum dose to be taken daily in divided amounts.

Dietary Sources
Bovine and Shark cartilage

Shiitake Mushrooms (as a constituent of chitin)

The best source is the supplemental form of Glucosamine sulfate

References
1.Mondoa, Emil I. MD and Mindy Kitei. Sugars that Heal. Ballantine Publishing, 2001.
2.Elkins, Rita MH. Miracle Sugars. Woodland Publishing, 2003.
3.Glycoscience website (This site prohibits direct linkage.)
4.http://www.lis.net.au/~dbird/glyconutrients.htm (A glyconutrient site by Dr David Bird MbChB, Dip Clinical Nutrition, FACNEM [Fellow of the Australian College of Nutritional and Environmental Medicine])
5.http://www.geocities.com/chadrx/glucosamine.html (Chad Bradshaw's site on Glucosamine)