A recent study by researchers at the University of Florida found that glucosamine, a popular over-the-counter joint supplement, was associated with a 25% higher likelihood of mild cognitive impairment progressing to dementia. The findings come from a large retrospective analysis of patient health records, supported by experiments involving human brain tissue and mouse models of Alzheimer's disease. The study was published in Nature Metabolism. The researchers analyzed deidentified health records collected from 2012 to 2024 and focused on patients diagnosed with either Alzheimer's disease and related dementias (ADRD) or mild cognitive impairment (MCI). In both groups, 8% of patients reported using glucosamine, including 1,896 people with ADRD and 2,750 people with MCI. After accounting for age, sex, and demographics, the researchers found that glucosamine use was associated with a 25% higher likelihood that MCI would progress to dementia. Among people who already had ADRD, glucosamine use was also associated with a 25% higher mortality risk, though this association was not observed in the MCI group. The health record findings do not show that glucosamine itself causes dementia to progress. Observational studies can reveal associations, but other differences between people who take a supplement and those who do not may contribute to the results. The researchers suggest that the findings raise an important clinical question that now deserves much more attention. The study also uncovered evidence of a biological mechanism that could help explain the association. The researchers point to a metabolic pathway involving the attachment of sugar structures to proteins. This process is a normal and important part of cell biology, but the researchers found signs that it becomes excessively active in Alzheimer's disease. The Alzheimer's brain appeared to be particularly vulnerable to this metabolic pathway. Mouse experiments showed that glucosamine significantly increased the attachment of sugar residues to proteins inside cells. At the same time, glucosamine-treated mice developed worse deficits in "social memory" compared with the other animals. When the researchers used a chemical treatment to suppress the sugar attachment process, memory performance improved. That experiment suggested that excessive sugar tagging could play a direct role in the memory problems seen in the animals rather than simply occurring alongside them. Human Alzheimer's brain tissue showed the same pattern. Brain specimens from people with Alzheimer's disease showed significantly more sugar attachment than tissue from normal controls. Combined with the mouse experiments and health record analysis, the findings suggest that abnormal metabolism may be more than a secondary consequence of Alzheimer's disease. The researchers reported that it could instead contribute to the disease process itself. The results raise a potentially important question about glucosamine use among people with cognitive impairment or dementia, but they do yet establish that people should stop taking the supplement. A controlled human clinical trial will be needed to determine whether glucosamine directly accelerates Alzheimer's progression and, if so, which patients may be most vulnerable.