The Effects of Glucosamine on Glucose Metabolism

Does administration of oral glucosamine, such as that found in joint supplements, affect glucose metabolism? The effects of oral glucosamine on glucose metabolism were recently summarized in a review article by Simon and coworkers (2011).

Glucosamine is a commonly used supplement for osteoarthritis in both humans and horses. Intestinal absorption of glucosamine in horses is 2.5-6% of the orally administered dose. From a chemical perspective, glucosamine is essentially glucose with an amino group (a precursor of protein). Glucosamine may enter into glucose pathways that affect insulin sensitivity and glucose uptake into cells.

Studies using high concentrations of glucosamine in media with cells grown outside the body showed that uptake of glucose by the cells was decreased. Experimental interference with glucose metabolism occurs when glucosamine concentrations are hundreds of times higher than those expected in the blood with normal supplemental doses of glucosamine. The only diabetes-like effect of glucosamine in humans occurred with high-dose intravenous infusion of glucosamine, which caused a slight elevation in plasma glucose concentration during an intravenous glucose tolerance test. The concentration of glucosamine needed to achieve this effect was very high, 500-1000 times the blood concentration expected after oral administration, and glucosamine concentration was nearly the same as plasma glucose concentration. The diabetes-like effect of glucosamine was not caused by insulin resistance, but rather inhibition of the enzyme glucokinase, which initiates the use of glucose to produce energy in cells. In animals, oral administration of glucosamine at doses much higher than those used for osteoarthritis did not adversely affect glucose tolerance.

This review of many studies concluded that trials involving glucosamine supplementation in humans with type 2 diabetes or impaired glucose tolerance found no clinically significant adverse effects on glucose metabolism or insulin sensitivity. Studies that have shown an effect of glucosamine to decrease insulin sensitivity are limited to intravenous administration of glucosamine and in cells studied outside the body. The authors concluded that currently there appears to be no reason to restrict the use of glucosamine in human patients at risk for diabetes, patients with either type 1 or type 2 diabetes, or in patients that have normal blood glucose concentration.

Horses are unlikely to absorb enough orally administered glucosamine to reach sufficiently high blood concentrations to interfere with glucose metabolism or induce insulin resistance. Ultimately, owners must balance the risk of insulin resistance versus improvement of osteoarthritis if an at-risk horse is supplemented with glucosamine. Based on experimental studies and human clinical trials, it appears this risk is slight.

Simon, R.R., V. Marks, A.R. Leeds, and J.W. Anderson. 2011. A comprehensive review of oral glucosamine use and effects on glucose metabolism in normal and diabetic individuals. Diabetes/Metabolism Research and Reviews 27:14-27.