Introduction: Human immunodeficiency virus (HIV)-infected patients treated with antiretroviral therapy (ART) are at high risk for vitamin D insufficiency, which is essentially caused by interference of medication with vitamin D metabolism. Under these conditions, the preservation of natural seasonal variability in vitamin D concentrations is not self-evident. Yet, for proper screening and interpretation of laboratory findings, knowledge about seasonality is essential. Aim of the study was to describe seasonal behavior in ART-treated HIV-infected patients in Central Europe.
Material and methods: It was a retrospective single-center study. Patients’ medical records were screened for serum vitamin D levels, β-crosslaps, and surrogate values of bone turnover.
Results: A total of 1011 datasets (625 patients) were evaluated. Overall, the median vitamin D level was 19.6 µg/l. In 207 (16.4%) datasets, patients were receiving oral cholecalciferol supplementation. Seasonal changes in serum vitamin D levels were reflected by minimum levels (median 13.5 µg/l) in March and maximum levels (median 23.7 µg/l) in July (p < 0.001). In contrast, serum calcium levels were lowest in September and October (2.23 mmol/l) and highest in May (2.32 mmol/l).
Conclusions: Significant variation in seasonal serum vitamin D levels was found in an unselected population of HIV-infected patients. This finding is in line with results from HIV-negative populations. Accordingly, the time point of vitamin D testing might be crucial for appropriate diagnosis of hypovitaminosis. We recommend vitamin D testing between December and May to provide the highest sensitivity. As serum calcium levels did not demonstrate the same pattern, the meaning of this finding is unclear and warrants further investigation.