Introduction:
Vitamin D is a pleiotropic hormone involved in the functioning of organ systems including those central to critical illness pathophysiology. We evaluated the longitudinal vitamin D status in the pediatric intensive care unit (PICU) and its relevance to patient outcomes.

Material and methods:
Thirty-six PICU-admitted patients and 40 age- and sex-matched healthy children were enrolled. Serum total 25-hydroxyvitamin D [25(OH)D] levels were analyzed on PICU days 1, 5, and 10 in the patient group, and once in the control group. Patients were divided into sufficient (> 30 ng/ml), insufficient (20–30 ng/ml), and deficient (< 20 ng/ml) subgroups. Outcome measures between the subgroups and alterations in 25(OH)D levels were examined.

Results:
The mean 25(OH)D levels of PICU patients initially and control cases were not different (25.4 ±6.0 and 25.9 ±5.8 ng/ml, respectively). Although all patients with vitamin D deficiency were hospitalized for infectious diseases, the mean 25(OH)D level of patients hospitalized for infections was not different from other patients. There was no difference between vitamin D subgroups in demographic variables, admission season, illness severity, respiratory/inotropic support, duration of stay, or mortality. Vitamin D deficient patients had lower albumin concentrations (p < 0.05). On days 5 and 10, the mean 25(OH)D levels of the patients were 24.5 ±5.7 and 23.6 ±5.8 ng/ml, respectively, both different from the admission level (p < 0.001).

Conclusions:
Hypovitaminosis D, which is common in healthy children, is also common in PICU admission and tends to be more profound during the stay. Further studies are required to evaluate the bioavailability of vitamin D in critical illness.