Vitamin D, parathyroid hormone and serum calcium levels and their association with hospital mortality in critically ill patients

Introduction

Vitamin D deficiency is highly prevalent and has been associated with increased mortality in the general population [1, 2]. Critically ill patients are especially prone to present with or develop low vitamin D levels due to their underlying disease, sunlight deprivation or longer hospital stays.

Methods

Parathyroid hormone (PTH) and vitamin D status (25-hydroxyvitamin D (25(OH)D)) were assessed at different ICUs (medical, cardiac surgery, mixed surgical and neurological) in 404 patients (age 63 ± 16 years, 65% male) from September 2008 until November 2009.

Results

The mean serum 25(OH)D level was 19.6 ± 11.2 ng/ml. Normal 25(OH)D levels (>30 ng/ml) were found in 12.4% of all patients. The majority (58.2%) were vitamin D deficient (<20 ng/ml), while 29.4% were considered vitamin D insufficient (>20 and <30 ng/ml) by current definitions. Significant variations of vitamin D levels occurred depending on season, with highest values found in August (27.1 ± 13.1 ng/ml) and the lowest in March (12.5 ± 4.6 ng/ml), respectively. Secondary hyperparathyroidism (PTH >65 pg/ml) was highly prevalent in medical and cardiac surgery patients (43.7% and 37.9%). In an age, sex and SAPS II score adjusted Cox-proportional hazards regression analysis model, patients with low PTH or serum calcium levels, as well as low 25(OH)D levels (cut-off 12 ng/ml) were all at significantly greater risk for all-cause mortality. With all variables included into one model (n = 268 patients) serum calcium remained an independent predictor of mortality, whereas PTH log (P = 0.08) and 25(OH)D (P = 0.16) levels suggested a trend.

Conclusions

Vitamin D deficiency is often encountered in critically ill patients. Higher than the currently recommended daily dose of 200 IU vitamin D₃ is probably required for achieving or maintaining normal 25(OH)D levels. Results of this study suggest that baseline parameters reflecting calcium/PTH status are associated with mortality. Whether a disturbance in calcium/vitamin D₃ or PTH metabolism develops secondary to the medical condition of ICU patients or is a primary cause of mortality remains to be clarified in prospective analyses.