The worry came from the lab; in people, resting sugar did not move
Glucosamine is a sugar and interferes with glucose handling in the lab. Gathering the human trials, including in people with diabetes, fasting sugar did not rise on ordinary doses.
What the study found
Fasting glucose held steady across trials running up to three years
Glucosamine is a sugar and interferes with glucose handling in laboratory systems, which is where the worry began. Gathering the human trials, including those in people with diabetes or pre-diabetes, fasting glucose did not rise on ordinary oral doses over periods reaching three years.
The caveat · Authors consult for industry clients
The reviewers work for a consultancy that carries out safety assessments for industry clients, and the paper names no client. In the same passage where they set aside the studies reporting a glucose effect, they acknowledge that no long-term trial exists in people with pre-diabetes.
What we don't know
A one-dose glucose challenge and months of resting glucose measure different things, so both results can stand. What neither covers is years of glucosamine in someone who is already glucose intolerant.