To evaluate the association between regular glucosamine intake and heart failure (HF) and to explore whether the association is mediated by relevant cardiovascular disease.We included 479,650 participants with data available for supplement use and without HF at baseline from the UK Biobank study. Using 12 single-nucleotide polymorphisms linked to HF, a weighted genetic risk score was calculated. We evaluated the association between glucosamine use and HF by Cox regression models after inverse probability of treatment weighting. A validation and mediation analysis were performed through two-sample Mendelian randomization. The study was from May 18, 2006, to February 16, 2018.During a median follow-up of 9.0 (IQR, 8.3-9.8) years, we documented 5501 incident cases of HF. In multivariable analysis, the HR of glucosamine users for HF was 0.87 (95% CI, 0.81 to 0.94). The inverse associations were stronger in males and participants with unfavorable lifestyle (P<.05 for interaction). Genetic risk categories did not modify this association (P>.05 for interaction). Multivariable Mendelian randomization showed that taking glucosamine was protective against HF (HR, 0.92; 95% CI, 0.87 to 0.96). The mediated proportion of coronary heart disease and stroke were 10.5% (95% CI, 7.6% to 13.4%) and 14.4% (95% CI, 10.8% to 18.0%), respectively. The two-mediator combination accounted for 22.7% (95% CI, 17.2% to 28.2%) of the effect of glucosamine use.Regular glucosamine supplementation was associated with a lower risk of HF regardless of genetic risk status, and to a lesser extent, coronary heart disease and stroke mediated this effect. The results may inform novel pathway for prevention and intervention toward HF.