Glucosamine, one of the most popular OTC supplements among older adults, is now under scrutiny for something far more serious than joint health. A large study published in Nature Metabolism, drawing on electronic health records from over 66,000 patients, found that glucosamine users had a 25% higher likelihood of progressing from mild cognitive impairment (MCI) to full dementia within 5 years — and a 25% higher mortality risk among those already diagnosed with dementia.

Researchers at the University of Florida used AI to analyze health records and paired those findings with postmortem human brain tissue and mouse model experiments. The proposed mechanism centers on glycosylation — a process where sugar structures are tagged onto proteins. In Alzheimer's brains, this system appears to go into overdrive, and glucosamine, which can cross the blood-brain barrier, may be fueling that excess. In mice, suppressing the process improved memory; administering glucosamine worsened outcomes.

Key Takeaways

• The association was observational — causality has not been established, and clinical trials are needed
• The mortality signal was seen only in patients with established dementia, not in the MCI group
• Experts recommend initiating conversations with at-risk patients (MCI or dementia) who are currently taking glucosamine

Why it matters: Glucosamine has never shown dramatic benefits for its primary use case, and now there's a meaningful signal linking it to worse cognitive outcomes. For clinicians managing older patients with cognitive concerns, this study is a prompt to revisit supplement lists — even the seemingly harmless ones.