Abstract
BACKGROUND: As research has identified a wide array of biological functions of vitamin D, the consequences of vitamin D deficiency in persons with chronic kidney disease has attracted increased attention. The objective of this study was to determine the extent of 25-hydroxyvitamin D (25-OH vitamin D) deficiency and its associations with self-reported physical activity and health-related quality of life (HRQoL) among participants of the Comprehensive Dialysis Study (CDS). METHODS: The nutrition substudy of the CDS enrolled patients new to dialysis from 68 dialysis units throughout the USA. Baseline 25-OH vitamin D concentration was measured using the Direct Enzyme Immunoassay (Immunodiagnostic Systems Inc.). Physical activity was measured with the Human Activity Profile (HAP); the Medical Outcomes Study Short Form-12 (SF-12) was employed to measure HRQoL. RESULTS: Mean age of the participants (n = 192) was 62 years. There were 124 participants (65%) with 25-OH vitamin D concentrations < 15 ng/mL, indicating deficiency, and 64 (33%) with 25-OH vitamin D ≥ 15 to <30 ng/mL, indicating insufficiency. After adjusting for age, sex, race/ethnicity, diabetes, season and center, lower 25-OH vitamin D concentrations were independently associated with lower scores on the HAP and on the Mental Component Summary of the SF-12 (P < 0.05 for both), but not with the Physical Component Summary of the SF-12. CONCLUSION: In a well-characterized cohort of incident dialysis patients, lower 25-OH vitamin D concentrations were associated with lower self-reported physical activity and poorer self-reported mental health.