Urine Calcium Excretion, Cardiovascular Events, and Mortality in Outpatients With Stable Coronary Artery Disease (from the Heart and Soul Study)

Abstract

We sought to evaluate the association of urine calcium excretion (UCaE), which reflects systemic calcium absorption, with cardiovascular (CV) events and mortality in outpatients with prevalent coronary heart disease (CHD). Calcium supplementation is associated with vascular calcification and adverse CV outcomes in patients with end-stage renal disease. Recent studies have raised concern that this phenomenon may also extend to the general population. However, previous studies have assessed oral calcium intake, which correlates poorly with systemic calcium absorption. We measured UCaE from 24-hour urine collections provided by 903 outpatients who were recruited from 2000 to 2002. We used Cox proportional hazard models to evaluate the association of baseline UCaE with a primary end point of any CV event (myocardial infarction [MI], heart failure, stroke, or CV mortality). During a mean follow-up of 6 ± 3 years, 287 subjects (32%) had a CV event. After multivariate adjustment for demographics, traditional CV risk factors, and kidney function, there was no association between UCaE and the primary end point of any CV event (per 10-mg/day greater UCaE, hazard ratio 1.00, 95% confidence interval 0.98 to 1.02). Evaluation of individual CV outcomes revealed a lower rate of MI with higher UCaE (hazard ratio 0.97, 95% confidence interval 0.94 to 1.00). In conclusion, greater UCaE is not associated with higher overall CV event rates or mortality in outpatients with stable CHD. On the contrary, greater UCaE is associated with a modestly lower rate of MI. These findings suggest that greater systemic calcium absorption does not confer CV harm in outpatients with prevalent CHD.