Association Between Post-Transplant Vitamin D, Metabolic Syndrome, and Post Transplant Diabetes Mellitus

Background: Associations between 25-hydroxyvitamin D (25(OH)D) deficiency and diabetes have been observed in the general population, but are less delineated in kidney transplant recipients (KTR), especially in the context of highly-prevalent metabolic syndrome (MetS) features in KTR. We hypothesized that vitamin D deficiency may present greater risk in KTR in those with greater burden of MetS features. Methods: We retrospectively evaluated 1792 KTR with no treated diabetes at transplant between 1998 and 2018. Vitamin D was measured at ≥3 months post transplant. MetS features were defined by National Cholesterol Education Program, Adult Treatment Panel III (NCEP-ATP III) criteria. The primary outcome was treated post-transplant diabetes mellitus (PTDM) incidence. Results: In 1792 non-diabetic KTR followed for 10956 patient-years, 237 patients developed PTDM. For KTR meeting NCEP-ATP-III criteria, with 4th-quartile 25(OH)D, there were 1.5 new diagnoses per 100 patient-years, versus 4.2 events per 100 patient-years in KTR with 1st-quartile 25(OH)D (p<0.001). In multivariate survival regression, vitamin D was, accounting for individual NCEP-ATP-III criteria, associated with PTDM (HR 0.93 per 10 nmol/mL 25(OH)D, p=0.007) independently of fasting blood sugar and HbA1c. In marginal effects analysis, MetS impact on PTDM increased as serum 25(OH)D levels decreased. Conclusions: Our study suggests that decreased 25(OH)D is associated with increased PTDM, and this marginal impact worsens as KTR have an increased burden of MetS.