In my readings it is better as a preventative than as a cure. Though it has been proven to stimulate production of sinovial fluid and help regenerate very small amounts of damage to cartilege. I do give Glucosamine/Chondroitin/MSM 1300 twice a day to my 73 lb Lab. I started when he was about 10 months old and in the middle of a three month long mystery limp and kept it up with my Vet's blessing.
If you google glucosamine and diabetes you'll probably get some hits. I think they will be old but there was a lot of talk, unsubstantiated as far as I could telll, about a link. Seems to have died down.