Background: Although serum phosphorus, calcium, and calcium-phosphorus product levels have been associated with cardiovascular events and mortality in patients with normal kidney function, most studies have not examined the association of these minerals with outcomes when collected repeatedly over time.
Methods: We evaluated the association of serum phosphorus, calcium, and calcium-phosphorus product levels with cardiovascular events and mortality in 950 participants of the Appropriate Blood Pressure Control in Diabetes trial by both time-dependent Cox regression models using the cumulative average of minerals measured over time and fixed covariate Cox regression models with only baseline values of these minerals.
Results: There were 42 deaths and 193 cardiovascular events among the participants, who were followed for an average of 4.8 years following randomization. A significant association was noted between baseline serum phosphorus >3.9 mg/dL and baseline calcium-phosphorus product >36.8 mg(2)/dL(2) compared with the lowest referent category with the adjusted risk of cardiovascular death (hazard ratio [HR] 5.00; 95% confidence interval [CI], 1.70-14.72) and (HR 10.01; 95% CI, 2.55-39.31), respectively. However, in time-dependent models using mineral values repeated during the course of the study, only the average of serum phosphorus remains significant (HR 4.25; 95% CI, 1.15 to 16.65).
Conclusions: In the Appropriate Blood Pressure Control in Diabetes cohort, serum phosphorus, but not serum calcium or calcium-phosphorus product, was associated with cardiovascular mortality in time-dependent Cox regression models. Thus, serum phosphorus levels may be more reliable in predicting cardiovascular mortality in patients with type 2 diabetes.