Association Between the Water Distribution in the Human Body and 25-Hydroxyvitamin D Among the Type 2 Diabetes Mellitus Population: A Possible Pathway Between Vitamin D and Diabetic Nephropathy

Abstract

Purpose To explore the association between the water distribution in the human body and 25-hydroxyvitamin D among patients with type 2 diabetes mellitus (T2DM), and to analyze whether water distribution is a mediator between vitamin D and T2DM complications. Patients and Methods In total, 533 T2DM inpatients were included from August 1, 2016 to April 1, 2023. Water distribution indicators, whether from the whole body, arms, trunk, or legs, were measured to calculate the association with vitamin D using linear regression analysis. Subgroups based on age, sex, body mass index, and macrovascular complications were established to clarify changes in the association between vitamin D and water distribution in different populations. Mediation analysis was applied to evaluate the correlation between vitamin D, water distribution, and T2DM complications. Results There was a negative correlation between 25-hydroxyvitamin D and the ratio of extracellular water (ECW)/total body water (TBW) both in the whole body ( P =0.045, β =−0.008) and in certain parts. A U-shaped restricted cubic spline curve further presented an inflection point (approximately 23 ng/mL 25-hydroxyvitamin D) in the relationship between 25-hydroxyvitamin D and the ECW/TBW of the whole body. A negative correlation was observed between ECW/TBW and vitamin D in the obese subgroup ( P =0.015, β =−0.038). In the total effect of vitamin D on diabetic nephropathy (DN), the mediation effect of ECW/TBW accounted for 15.44%. Conclusion A correlation between vitamin D and water distribution was observed, and a high ECW/TBW was one of the pathways through which low vitamin D levels might affect DN.