The disease-slowing claim rests on two trials sharing one sponsor
Over three years, knees on 1,500 mg of glucosamine sulfate narrowed less than placebo knees, which lost 0.19 and 0.31 mm, in two trials sharing a design, a preparation and a sponsor.
What the study found
Two three-year trials found knees narrowed less on glucosamine
Knees on 1,500 mg of glucosamine sulfate a day narrowed less over three years than knees on placebo, which lost 0.19 and 0.31 mm of joint space. The two trials share a design, a preparation and a sponsor, and are the source of the idea that glucosamine changes the disease.
The caveat · The two groups' ranges overlap
The two arms' confidence intervals overlap substantially, so the striking loss-versus-no-loss framing compares each arm against zero rather than against the other. Around 200 people is small for a three-year X-ray endpoint. Both sit in the stratum later analyses found produces larger effects.
What we don't know
Every trial measuring joint structure independently of the manufacturer found nothing, but those ran shorter and used another salt. Nobody has repeated the three-year sulfate trial without its manufacturer.