Relationship of serum calcium concentration with chronic kidney disease and mortality in type 2 diabetes mellitus patients: evidence from the NHANES 1999-2018.

Objectives: This study aims to explore the relationship of serum calcium (Ca) concentration with diabetic kidney disease (DKD) and all-cause mortality among type 2 diabetes mellitus (T2DM) patients using National Health and Nutrition Examination Surveys (NHANES).

Methods: Data of T2DM patients aged ≥ 40 years were screened from the NHANES database from 1999 to 2018. The outcomes were the risk of DKD diagnosed by urine albumin-to-creatinine ratio (UACR) ≥ 30 mg/g or estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m² and the risk of all-cause mortality ascertained by linkage to National Death Index (NDI) records through 31 December 2019. The weighted univariate and multivariate logistic regression model and cox proportional hazard model were utilized to explore the relationships of serum Ca concentration with DKD and all-cause mortality, respectively, with odds ratios (ORs), hazard ratios (HRs) and 95% confidence interval. The relationships were further explored stratified by age, gender, body mass index (BMI), the duration of T2DM, and the history of cardiovascular disease (CVD), cancer and DKD.

Results: Totally, 6595 T2DM patients were included. Of these patients, 2441 (37.01%) had DKD and 1868 (28.32%) deaths occurred over a mean follow-up of 104.50 (± 1.61) months. In fully adjusted model, we observed high serum Ca concentration was associated with high risk of DKD (OR = 1.45, 95% CI 1.18-1.77) and high all-cause mortality risk (HR = 1.33, 95% CI 1.16-1.52). These relationships remained significant after performing subgroup analyses. The Restricted cubic spline curves shown that linear correlations were observed between serum Ca concentration and DKD as well as all-cause mortality (P < 0.05).

Conclusions: Elevated serum Ca concentration may predict the high risk of DKD and poor prognosis in T2DM patients, and future large-scale and well-designed prospective cohort study is needed to explore the association of serum Ca concentration and DKD and prognosis in T2DM patients.