Background: There are seasonal variations in serum 25-hydroxyvitamin D (25OHD) levels related to sun exposure. Recent guidelines suggest a target serum 25OHD level >30 ng/ml in chronic kidney disease patients. However, vitamin D supplementation dosing and monitoring regimens are not well established in hemodialysis patients. The aim of this study was to assess the interplay between season and 25OHD supplementation according to guidelines on 25OHD levels in hemodialysis patients.
Methods: We retrospectively reviewed data collected prospectively over 12 months in 32 stable hemodialysis patients receiving 25OHD supplements (mean dose 30,600 IU/month) under routine clinical care following the Spanish Society of Nephrology guidelines.
Results: Higher serum 25OHD was observed during the summer, peaking in June and August. Despite a trend towards a higher 25OHD dose in winter the prevalence of 25OHD deficiency was still >40 % in winter. Furthermore, despite a higher dose of calcium-based phosphate binders, there was a trend toward lower serum calcium in winter. Season, together with residual diuresis and dry weight, was a significant independent contributor to a multivariate lineal regression model that explained 25 % of serum 25OHD variability, while a 25OHD dose did not contribute significantly in this 25OHD-supplemented population.
Conclusion: Winter vitamin D deficiency is prevalent in hemodialysis patients despite supplementation with 25OHD according to clinical guidelines. More intensive monitoring or pre-emptive winter dose increases should be evaluated to achieve guideline targets.