I was thinking that glucosamine came from sources like red meat and bones, and since I could use a little joint lubrication myself, I just googled these. I found an interesting quick read at
Sources of Glucosamine & Chondroitin
Here is an exert: "Don't be fooled by the price or size of the pills because what counts is quality not quantity. Be an informed consumer and research the brand of chondroitin or glucosamine your interested in. This quick research can make a world of a difference in terms of decreasing your joint pain and discomfort."
By the way, in the two articles I read, there is conflicting information, so be sure to read several sources to see if you can get the real scoop.
From
Glucosamine/Chondroitin: Introduction :
"There are no food sources of glucosamine. The only natural sources are in your body and in chitin (the exoskeleton of shellfish -- crab, lobster, shrimp, and so on)."
This could be important (if true) if you are allergic to shellfish and the glucosamine label says it comes from natural sources.