ACADEMIC EMERGENCY MEDICINE 2011; 18:551–554 © 2011 by the Society for Academic Emergency Medicine
Objectives: Vitamin D is increasingly recognized as an important mediator of immune function and may have a preventive role in the pathogenesis of sepsis. We sought to evaluate the association between vitamin D status and sepsis severity and hypothesized that vitamin D insufficiency would be associated with increased sepsis severity.
Methods: This was a pilot study of emergency department (ED) patients age ≥18 years evaluated for suspected infection at an urban, teaching hospital. The authors measured illness severity using the following assessments at baseline and 24 hours: 1) severe sepsis, defined as suspected infection plus two or more elements of systemic inflammatory response syndrome criteria and acute dysfunction of one or more organ systems; 2) Acute Physiology Age Chronic Health Evaluation (APACHE) II scores; and 3) Sepsis-related Organ Failure Assessment (SOFA) scores. Vitamin D insufficiency was defined as baseline serum 25-hydroxyvitamin D (25OHD) levels <75 nmol/L.
Results: Eighty-one patients were enrolled, with a median age of 62 years (interquartile range [IQR] = 48–76 years), 47% were female, and 77% were white. At baseline, 64 (79%) had 25OHD levels of <75 nmol/L, and 43 (53%) had severe sepsis. At 24 hours, 48 (59%) had severe sepsis. Patients with baseline 25OHD levels of <75 nmol/L, compared to patients with 25OHD levels of ≥75 nmol/L, were more likely to have severe sepsis (61% vs. 24%; p = 0.006) and SOFA scores ≥2 (44% vs. 18%; p = 0.049). Additionally, at 24 hours, those with 25OHD levels of <75 nmol/L were more likely to have severe sepsis (67% vs. 29%; p = 0.005), dysfunction of two or more organ systems (50% vs. 18%; p = 0.02), APACHE II score of ≥25 (19% vs. 0%; p = 0.06), and SOFA scores of ≥2 (63% vs. 29%; p = 0.02). Additionally, all four patients who died during the index hospitalization had 25OHD levels of <75 nmol/L.
Conclusions: Vitamin D insufficiency was associated with higher sepsis severity in ED patients hospitalized for suspected infection. Larger observational studies, mechanistic studies, and ultimately randomized controlled trials are needed to determine causation and to evaluate if vitamin D supplementation can reduce the risk of sepsis as a preventive or therapeutic strategy.
While vitamin D is best known for its regulation of calcium-phosphate homeostasis and effects on bone health, recent studies suggest that it also regulates innate and adaptive immune function, including differentiation and activation of macrophages, dendritic cells, and lymphocytes.1 Well described is the ability of 25-hydroxyvitamin D (25OHD), the primary circulating form, to induce its own conversion to the active form 1,25-dihydroxyvitamin D (calcitriol) and produce cathelicidin antimicrobial peptides in the presence of an antigen challenge.2 Accordingly, low serum 25OHD levels have been linked to increased risk of infection,3 and a recent clinical trial demonstrated that vitamin D supplementation reduced the risk of incident influenza A infection.4
In addition to infection prevention, vitamin D insufficiency may also be important in the pathogenesis of sepsis, the most fatal consequence of severe infection. In vitro and animal models of sepsis suggest that vitamin D treatment modulates proinflammatory cytokine production, deranged coagulation, and activation of the vascular endothelium associated with the sepsis syndromes.5,6 Although 77% of the U.S. population has insufficient vitamin D (serum 25OHD levels of <75 nmol/L) to support normal immune function,7 critically ill individuals with sepsis may have even lower 25OHD levels, compared to healthy controls.8
Vitamin D supplementation is a simple intervention that holds the potential to reduce illness severity in patients with infection. However, the association between vitamin D insufficiency and infection severity is not known. We hypothesized that among emergency department (ED) patients with suspected infection, those with vitamin D insufficiency, defined as serum 25OHD levels of <75 nmol/L, would have higher infection severity than those with 25OHD levels of ≥75 nmol/L.
This was a prospective observational pilot study. This study was approved by our institutional human subjects committee and informed consent was obtained.
Study Setting and Population
The population was a convenience sample of patients age ≥18 years presenting to the ED with hospital admission planned for suspected infection. Suspected infection was defined as a clinical suspicion of an infectious etiology as determined by the treating clinician. The setting was Beth Israel Deaconess Medical Center, an urban, teaching hospital with an emergency medicine residency training program.
Study procedures are as previously described.9 Briefly, treating clinicians notified study staff of patients with suspected infection; patients were then recruited for the study during their ED stay with clinical and laboratory measures assessed at two time points: baseline (in the ED) and 24 (±2) hours later. Patients were classified as having “sepsis” if they had suspected infection plus two or more elements of systemic inflammatory response syndrome criteria and “severe sepsis” if they had sepsis plus acute dysfunction of one or more organ systems. Additional markers of illness severity included the Acute Physiology Age Chronic Health Evaluation (APACHE) II, and Sepsis-related Organ Failure Assessment (SOFA) scores, which are validated and frequently used scales to measure severity of medical illness and infection, respectively.10,11 All assessments were made based on worst parameters in the ED (for baseline time point) or during the first 24 hours (for the 24-hour time point). If a patient was discharged before 24 hours or a sample was unavailable at 24 hours, the closest assessment before that time was carried forward for analysis. Outcome assessors were blinded to vitamin D status and to the objective of this study.
Serum samples were promptly refrigerated at −4°C and transferred to −80°C freezers for long-term storage within 24 hours. The 25OHD levels were measured by liquid chromatography–tandem mass spectrometry in the Massachusetts General Hospital laboratory. The between-run coefficient of variation for a quality control serum with 25OHD concentration of 57 nmol/L is 7.5%. Serum lactate levels were assessed either by the hospital laboratory or using a point-of-care i-STAT system (Abbot Lifesciences Point of Care, Princeton, NJ). Activation of the inflammatory cascade was assessed using established markers of the body’s inflammatory response (interleukin [IL]-1β and IL-6). These levels were measured at baseline using Quantikine enzyme-linked immunosorbent assay kits (R&D Systems, Minneapolis, MN).
We performed statistical analyses using Stata 10.1 (StataCorp, College Station, TX) and summarized data using basic descriptive statistics. Vitamin D status was defined by 25OHD levels as insufficient (<75 nmol/L) or sufficient (≥75 nmol/L), based on prior analysis of vitamin D and immune responses2 and previous epidemiologic data.3,7 APACHE II and SOFA scores were also dichotomized based on established thresholds to facilitate clinically relevant comparisons. We compared illness severity by vitamin D status using chi-square tests, or Fisher’s exact test as appropriate, and continuous laboratory measurements by Student’s t-test. All p-values were two-tailed, with p < 0.05 considered statistically significant. For this hypothesis-generating pilot study, we did not correct for multiple comparisons. Because age was a large potential confounder of the vitamin D sepsis severity association, we adjusted the primary results for age using standard multivariable logistic regression, with 25OHD level and age as predictors. We assessed model goodness of fit using the Hosmer-Lemeshow test.
We enrolled 81 patients, who were median age 62 years (interquartile range [IQR] = 48–76 years), 47% female, and 77% white. At baseline, 16 (20%) had infection without sepsis, 22 (27%) had sepsis, and 43 (53%) had severe sepsis. At 24 hours, 20 (25%) had sepsis and 48 (59%) had severe sepsis. The median serum 25OHD level was 52 nmol/L (IQR = 32–71 nmol/L), with 64 (79%) having vitamin D insufficiency defined by 25OHD level of <75 nmol/L.
Demographic and clinical characteristics, stratified by vitamin D status, are presented in Table 1. Vitamin D insufficiency was associated with all markers of illness severity at the baseline and 24-hour time points, and with an increase in SOFA score from baseline to 24 hours. While vitamin D insufficiency was associated with older age, adjusting for age did not materially change the direction of any effect sizes (Table 2). Additionally, all four patients who died during the index hospitalization had 25OHD levels of <75 nmol/L.
|Characteristic||Serum 25OHD Level (nmol/L)||p-value|
|<75, n (%)||≥75, n (%)|
|Age ≥ 65 years||34 (53)||4 (24)||0.03|
|Female sex||27 (42)||11 (65)||0.10|
|Nonwhite race||14 (22)||5 (29)||0.53|
|Severe sepsis||39 (61)||4 (24)||0.006|
|SOFA score ≥ 2||28 (44)||3 (18)||0.049|
|Severe sepsis||43 (67)||5 (29)||0.005|
|Two or more organ system dysfunction||32 (50)||3 (18)||0.02|
|APACHE II score ≥ 25||12 (19)||0||0.06|
|SOFA score ≥ 2||40 (63)||5 (29)||0.02|
|Increase in SOFA score (baseline to 24h)||29 (45)||3 (18)||0.04|
|Characteristic||Unadjusted Odds Ratio* (95% CI)||Age-adjusted Odds Ratio* (95% CI)|
|Severe sepsis||0.20 (0.06–0.67)||0.26 (0.07–0.96)|
|SOFA score ≥ 2||0.28 (0.07–1.05)||0.34 (0.09–1.34)|
|Severe sepsis||0.20 (0.06–0.65)||0.28 (0.08–1.01)|
|Two or more organ system dysfunction||0.22 (0.06–0.82)||0.30 (0.07–1.25)|
|APACHE II score ≥ 25||NC||NC|
|SOFA score ≥ 2||0.25 (0.08–0.80)||0.35 (0.10–1.24)|
|Increase in SOFA score (baseline to 24h)||0.26 (0.07–0.99)||0.34 (0.85–1.36)|
Although the study was underpowered to detect smaller differences in laboratory parameters statistically, patients with baseline 25OHD levels of <75 nmol/L, compared to patients with 25OHD levels of ≥75 nmol/L, had higher mean initial lactate levels (2.6 vs. 2.2 mmol/L; p = 0.20), IL-1 levels (3.1 vs. 1.4 pg/mL; p = 0.19), and IL-6 levels (276 vs. 148 pg/mL; p = 0.11).
To our knowledge, this is the first study to evaluate the association between vitamin D status and sepsis severity. In a cohort of ED patients with suspected infection, vitamin D insufficiency was consistently associated with severe sepsis, APACHE II scores, and SOFA scores. Additionally, vitamin D insufficiency was associated with worsening clinical course, as measured by increase in SOFA score from baseline to 24 hours.
Laboratory and animal studies provide support for our hypothesis that vitamin D may have an important protective effect in the pathogenesis of sepsis. For example, vitamin D pretreatment of human microvessel endothelial cells reduced lipopolysaccharide-induced production of proinflammatory cytokines (IL-6 and IL-8) and inhibited NF-κB activation.5 In the present clinical study, our results also suggest that higher 25OHD levels may be associated with lower systemic levels of proinflammatory cytokines, such as IL-1 and IL-6, although these nonsignificant results require further study. Additionally, Møller and colleagues6 found that 1,25-dihydroxyvitamin D3 supplementation improved sepsis-induced coagulation disturbances in a rat cecal ligation and puncture model. Although we did not assess coagulation in this study, these data suggest another possible mechanism of vitamin D-modulated protection against the pathogenesis of sepsis.
Severe sepsis affects more than 750,000 Americans annually, of whom 51% require intensive care unit assistance and 29% die during the index hospitalization.12 Despite years of research, the treatment of patients with severe sepsis remains an important challenge. To date, therapies that inhibit individual components of the inflammatory or coagulation pathways have had little impact on survival. The present results add to the existing literature suggesting that vitamin D is associated with sepsis severity. Further studies are needed to determine the role of vitamin D in prevention of infection and mitigation of the inflammatory and coagulation associated with sepsis.
Vitamin D supplementation, particularly of higher risk populations such as older adults, holds the potential to lower risk of incident infection and associated morbidity such as sepsis. In addition to prevention, vitamin D supplementation in the acute care of patients with infection has potential as an adjuvant treatment to modulate inflammatory and coagulation-induced sepsis syndromes. Vitamin D supplementation is a simple and safe intervention. In the present study, and consistent with prior epidemiologic data from the U.S. population,7 79% of patients had 25OHD levels of <75 nmol/L, below what is likely needed for optimal immune function. These hypotheses require further study through larger observational studies to confirm the present findings and ultimately randomized controlled trials of vitamin D supplementation.
As a pilot study, this analysis was exploratory in nature, as our modest sample size was underpowered to perform robust multivariable analyses or other inferential analyses. Although adjusting for age did not materially change results, other factors may have confounded the associations between vitamin D status and illness severity. Larger studies are needed to assess the effects of other potential confounders, such as season, obesity, and medical comorbidities. This was an observational study, and the reported associations do not prove causal relationships. Specifically, although we are not aware of any evidence that serum 25OHD levels change acutely in response to severe illness, it is difficult to address this issue (potential reverse causation) in this observational study. Clinical trials are needed before vitamin D supplementation can be recommended to prevent infection and resulting sepsis.
Vitamin D insufficiency was associated with higher sepsis severity in ED patients hospitalized for suspected infection.