Do glucosamine and chondroitin worsen blood sugar control in diabetes?

A recent study examined insulin and glucose levels with and without the simultaneous ingestion of 1500 mg of glucosamine. Sixteen fasting volunteers with osteoarthritis but without known diabetes or glucose intolerance received 7 g of glucose with or without ingestion of 1500 mg glucosamine sulfate. The authors unexpectedly uncovered undiagnosed diabetes or impaired glucose tolerance in 3 subjects. These 3 subjects showed a statistically significant (P=.04) 31% increase in the area under the curve of glucose levels following the test. There was no effect of glucosamine sulfate ingestion on patients with normal baseline glucose testing or on insulin levels. Their results might be important since they are the first to suggest that glucosamine ingestion may affect glucose levels in individuals who have untreated diabetes or glucose intolerance.⁵

One double-blinded RCT evaluated whether oral glucosamine supplementation altered glycosylated hemoglobin (HbA_1c) concentrations for patients with well-controlled diabetes mellitus. Thirty-eight patients were randomized to receive either treatment with glucosamine/chondroitin at the recommended doses or placebo. After 3 months of treatment HbA_1c levels did not change and were not significantly different between groups (P=.2).⁶

Another study addressed whether glucosamine taken at recommended doses for the treatment of osteoarthritis had any detrimental effect on glucose metabolism. Fourteen patients participated and had a baseline 4-hour meal tolerance test and a frequently sampled intravenous glucose tolerance test, before and after 4 weeks of glucosamine sulfate treatment (500 mg orally 3 times daily). After 4 weeks they found no change in fasting plasma glucose, insulin, glucose tolerance, or difference in insulin sensitivity in the group of subjects.⁷ Again, the study was limited by a small subject number and short duration of study.

Recommendations from others

The PDR for Nonprescription Drugs and Dietary Supplements states that “glucosamine is likely safe for patients with diabetes that is well controlled with diet only or with one or two oral antidiabetic agents (HbA_1c less than 6.5%). For patients with higher HbA_1c concentrations or for those requiring insulin, closely monitor blood glucose concentrations.”⁸

The American Pain Society encourages adults with osteoarthritis to take 1500 mg of glucosamine daily as a dietary supplement but does not specifically recommend it as pharmacologic management for pain.⁹ The American College of Rheumatology Subcommittee on Osteoarthritis has no recommendations regarding the use of glucosamine or chondroitin in the treatment of knee osteoarthritis.¹⁰