Role of vitamin d nutrition (VDN) in hyperparathyroidism of chronic kidney disease stages 2 to 5, a retrospective cohort study of 977 patients.

Objective: To determine the effect of vitamin D nutrition (VDN), as assessed by serum 25- hydroxyvitamin D (25OHD) on the degree and severity of secondary hyperparathyroidism, as assessed by serum PTH level in a cohort of patients with CKD stages 2-5. Methods: This is a retrospective study of patients with CKD who were seen at Henry Ford Hospital nephrology clinic between January 1 and December 31st, 2016. Patients were divided into four groups - stages 2, 3, 4 and 5 CKD. Data including demographics, eGFR, serum creatinine, PTH, calcium, 25-hydroxyvitamin D were collected for each group. Statistical analysis was done using ANOVA and multiple regression/ANCOVA analysis. Results: A total of 977 patients were included in the analysis. The mean serum PTH level increased significantly with CKD stage (50, 77, 137 and 355, p\u3c0.001), but serum 25-hydroxyvitamin D did not (26, 29, 30, 27, p=0.204). However, in multiple linear regression analysis, CKD stage (p\u3c0.001), lower calcium (p=0.005), African-American race (p=0.024) and lower 25-hydroxyvitamin D (p=0.005) were significant predictors of serum PTH levels. We did not have the details of vitamin D intakes so the small effect size could have been confounded by variable rate and dose of vitamin D intakes. In other modeling, the relationship of 25-hydroxyvitamin D to PTH varied by CKD stage. Conclusion: VDN, as assessed by serum 25-hydroxyvitamin D, may contribute to the secondary hyperparathyroidism in addition to CKD stage and prevailing serum calcium levels. Further studies, both prospective and interventional, would be necessary to determine the relative role of VDN independent of CKD stages