Glucosamine is currently one of the most popular of all dietary supplements. It is marketed as a treatment for arthritis, and there is some evidence that it is moderately helpful for this indication. But evidence had been accumulating to suggest that glucosamine might have other effects as well. The latest analysis evaluated the associations of regular glucosamine use with all-cause and cause-specific mortality in a large prospective cohort.
This population-based prospective cohort study included 495 077 women and men from the UK Biobank study. Participants were recruited from 2006 to 2010 and were followed up through 2018. The investigators evaluated all-cause mortality and mortality due to cardiovascular disease (CVD), cancer, respiratory and digestive disease. Hazard ratios (HRs) and 95% CIs for all-cause and cause-specific mortality were calculated using Cox proportional hazards models with adjustment for potential confounding variables.
At baseline, 19.1% of the participants reported regular use of glucosamine supplements. During a median follow-up of 8.9 years (IQR 8.3-9.7 years), 19 882 all-cause deaths were recorded, including 3802 CVD deaths, 8090 cancer deaths, 3380 respiratory disease deaths and 1061 digestive disease deaths. In multivariable adjusted analyses, the HRs associated with glucosamine use were 0.85 (95% CI 0.82 to 0.89) for all-cause mortality, 0.82 (95% CI 0.74 to 0.90) for CVD mortality, 0.94 (95% CI 0.88 to 0.99) for cancer mortality, 0.73 (95% CI 0.66 to 0.81) for respiratory mortality and 0.74 (95% CI 0.62 to 0.90) for digestive mortality. The inverse associations of glucosamine use with all-cause mortality seemed to be somewhat stronger among current than non-current smokers (p for interaction=0.00080).
The authors concluded that regular glucosamine supplementation was associated with lower mortality due to all causes, cancer, CVD, respiratory and digestive diseases.
Previous epidemiological investigations indicated that glucosamine use might play a role in prevention of cancer, cardiovascular disease and other diseases. This suggests that the finding is more than the result of a large ‘fishing expedition’ to which epidemiological studies are sadly prone. It we are indeed dealing with a true phenomenon, we should ask by what mechanism these remarkable outcomes might be achieved. It is well documented that glucosamine has powerful anti-inflammatory effects. Therefore it is conceivable that such anti-inflammatory mechanisms are the cause for the observed outcomes.
How do we prove or disprove the hypothesis that glucosamine reduces the mortality of a range of diseases? A reasonable starting point would be to consult the good old Hill criteria of causality:
(1) The strength of association is small to moderate – certainly not strong
(2) The consistency of the findings is quite remarkable; that is unless dozens of epidemiological studies that failed to yield and association were never published.
(3) The specificity of the association with diseases linked to inflammation is also impressive (with the caveat above).
(4) Temporality seems also not a problem, as far as I can see.
(5) Biological gradient needs further testing, I think.
(6) Plausibility is not a problem, since there is a possible mechanism that could explain the findings.
(7) The same applies to coherence.
(8) Experiment is needed, but it is far from easy to conduct clinical trials where mortality is an endpoint.
(9) Analogy is realised through the well-established concept of (cardiovascular) risk factors.
What does all this actually mean?
It means, I think, that glucosamine could well have clinical effects that go far beyond easing the pain of arthritis. However, we cannot be sure. Once again, it boils down to the need of robust clinical trial data. The subject certainly seems important enough to consider this option.