Association Between Calcium Supplementation and Recurrence of Cardiovascular Events in Patients With Cardiovascular Disease: A Population‐Based Cohort Study

BACKGROUND: The cardiovascular safety of calcium supplements in individuals with major cardiovascular disease (CVD) remains unclear. This study investigated the association between calcium supplementation and the risk of CVD recurrence in patients with established CVD. METHODS: A retrospective population-based study was conducted in Hong Kong of individuals aged ≥40 years newly diagnosed with CVD from January 1, 2006, to December 31, 2015. The treatment group consisted of patients with CVD prescribed calcium supplements, while the control group consisted of those who never prescribed calcium supplements from January 1, 2005, to December 31, 2020. Propensity score matching and Cox proportional hazard models were adopted to balance the baseline characteristics and estimate hazards ratios (HRs) for CVD recurrence. RESULTS: The matched cohort included 17 720 patients with CVD in each arm. Calcium supplementation was associated with an increased risk of recurrence of adverse CVD events (HR, 1.10 [95% CI, 1.07-1.14]) and CVD-related hospitalization or accident and emergency department attendance (HR, 1.16 [95% CI, 1.13-1.20]). Calcium-only supplementation had higher CVD recurrence risk (HR, 1.21 [95% CI, 1.17-1.25]) than the combination of vitamin D (HR, 0.97 [95% CI, 0.93-1.01]), and a more pronounced association was observed in men (HR, 1.15 [95% CI, 1.09-1.20]) than women (HR, 1.07 [95% CI, 1.03-1.11]). CONCLUSIONS: In patients with major CVD, calcium supplementation is associated with an increased risk of CVD recurrence, particularly with calcium-only use and in men. Caution should be exercised when prescribing or using calcium supplements among patients with CVD.