Glucosamine is a compound that may help to prevent the pain and disability of osteoarthritis. Its metabolism -- and, more specifically, its absorption in the intestines, distribution to body tissues, cellular uses, and excretion -- is not terribly well-studied; most data is decades old and much has been derived from animal studies. However, glucosamine metabolism is understood well enough to recommend its use as a nutritional supplement.
About Glucosamine
Glucosamine is a naturally occurring compound that is found in the synovial fluid and cartilage lining your joints. Although data supporting its use is limited and occasionally drawn from poorly designed studies, the general consensus is that glucosamine may have some effect on the development and progression of osteoarthritis, and that people with osteoarthritis who want to try glucosamine should not be advised against doing so.
Absorption
Glucosamine from oral supplements is absorbed relatively well in the intestines -- about 90 percent of it winds up in your blood, according to J.W. Anderson and colleagues, writing in the February 2005 issue of "Food and Chemical Toxicology." However, everything absorbed by your intestines undergoes a process called "first-pass" metabolism in your liver before it is distributed to target tissues -- in this case, your joints. First-pass metabolism of glucosamine is quite extensive, so that only about 25 percent of an oral dose makes it to your joints.
Distribution
Once glucosamine is in your blood, it is rapidly internalized by all cells with glucose transporters on their surfaces. This is the same transporter esponsible for glucose uptake from blood, and just like glucose, glucosamine uptake is increased by insulin. Although the serum half-life of glucosamine -- that is, the time it takes for blood glucosamine concentration to drop by one-half -- is short, the tissue half-life is likely much longer, according to MD Consult, which maintains a drug metabolism database.
Metabolism
Once inside cells, glucosamine plays an important role in glycolosis, say J.W. Anderson and colleagues. Glycolysis is part of a process that turns glucose into useable energy for your body, and it involves many steps and many different molecules. Once inside a cell, glucosamine can be converted into several intermediaries in the glycolytic process, depending on which intermediaries are needed by the cell at that particular time.
Excretion
The major pathways for excretion in your body are in the urine, in the stool, and in exhaled carbon dioxide. Carbon dioxide is not an intuitive "excretion" source; however, any compound in your body that contains carbon and oxygen can theoretically be broken down to produce some carbon dioxide. According to J.W. Anderson and colleagues, in an analysis of routes of glucosamine excretion, about half of it was excreted as carbon dioxide, about 40 percent as urine, and only a small amount was excreted as stool.
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