Glucosamine Linked to Faster Alzheimer's Progression in People With Mild Cognitive Impairment
A University of Florida study published in Nature Metabolism found that glucosamine supplements were associated with a 25% higher risk of progressing from mild cognitive impairment to dementia, and higher mortality among those already diagnosed with dementia. Researchers caution the observational findings are a safety signal, not proof of causation, and do not suggest a risk for cognitively healthy people taking glucosamine for joint health.
Older adults who take glucosamine for joint pain may face a higher risk of cognitive decline if they already have mild cognitive impairment, according to a new study from University of Florida researchers published in Nature Metabolism. The analysis found that glucosamine users with mild cognitive impairment were 25% more likely to progress to dementia than similar patients who did not take the supplement.
The research team examined thousands of medical records from patients with dementia, Alzheimer's disease and mild cognitive impairment, then narrowed the group to those taking glucosamine. Among people who already had dementia, glucosamine users showed higher mortality compared with non-users. The study also tracked laboratory mouse models and compared healthy human brains with Alzheimer's-affected tissue.
The findings center on glycosylation, a natural process in which brain cells attach small chains of sugar to proteins. Ramon Sun, Ph.D., a professor of biochemistry and molecular biology at the University of Florida College of Medicine and senior author of the study, compared these sugar chains to labels and fittings on a machine part. «The right amount is essential,» he said, explaining that the chains help proteins fold correctly, reach the right location in the cell and connect with their partners.
According to Sun, the body uses an internal checkpoint to regulate how many of these sugar chains it produces. Supplemental glucosamine bypasses that front gate entirely, he said, like a delivery truck pulling straight up to the loading dock and instantly boosting the raw material used to make the chains. In brain tissue, researchers found an excess of sugar chains on proteins in Alzheimer's-affected brains. Many of those proteins help nerve cells communicate, and the extra chains may interfere with their function. Sun likened the effect to coating a key in too much wax — it remains the same key but no longer fits the lock properly.
In mouse experiments, normal mice given glucosamine showed no increase in these sugar chains and no change in a memory test. But in mice with Alzheimer's-like disease, where the production line was already running too hot, glucosamine increased the sugar chains further and worsened performance on a memory test.
Neil Levin, senior nutrition education manager at the Illinois-based supplement manufacturer Now, said glucosamine is a naturally occurring compound of sugar and an amino acid group that serves as a fundamental structural building block in the body. It is concentrated in cartilage, the connective tissue that cushions joints, and is a component of larger molecules that give cartilage strength, elasticity and the ability to retain water. «Support for aging joints is the primary reason people take glucosamine as a dietary supplement,» Levin said.
Both researchers stressed the study's limits. The findings rely on medical records, which may not capture every supplement a patient took. «Health records tell us what was documented, not everything a person took,» Sun said, noting that over-the-counter supplements are not always recorded and that records do not reliably capture dose, brand or consistency of use. Levin added that glucosamine users may differ in factors such as arthritis, pain, mobility, frailty and medication use. He said the finding should be treated as a safety signal warranting controlled human research, but that it did not and could not conclude that glucosamine causes Alzheimer's disease.
The study did not examine cognitively healthy people and does not suggest that glucosamine poses a risk to those who take it for joint health. «A brain affected by dementia and a healthy brain are different biological environments, and we shouldn't assume a supplement behaves the same way in both,» Sun said. The next step, he added, is a well-designed, double-blind clinical trial to evaluate glucosamine's impact on cognitive decline in patients with dementia.
Sun advised anyone with a diagnosis of cognitive impairment or dementia who takes glucosamine to raise it at their next medical visit as part of an ordinary conversation about what is in the medicine cabinet. He also emphasized consulting a doctor before starting or stopping any supplement. «For now, the evidence isn't strong enough to recommend any supplement for slowing Alzheimer's disease, which is why doing this research properly, including the clinical trial we've called for, matters,» he said.
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