Nonspecific pain is a marker for hypovitaminosis D in patients undergoing evaluation for sleep disorders: a pilot study

BACKGROUND The purpose of this cross-sectional study was to test the hypothesis that serum vitamin D levels are abnormally low in sleep clinic patients admitting to chronic nonspecific musculoskeletal pain and to assess the associated risk factors. A secondary purpose was to identify a clinical biomarker for vitamin D deficiency. METHODS We enrolled 153 consecutive patients who admitted to the presence of chronic nonspecific musculoskeletal pain during a comprehensive sleep evaluation at a specialist sleep medicine clinic within an academic center. Venous blood sampling was performed for determination of serum 25-hydroxyvitamin D. Risk factors for vitamin D deficiency (25-hydroxyvitamin D < 20 ng/mL) were identified by odds ratios. Receiver-operating characteristic curve analysis was performed with 10-fold cross-validation to identify a biomarker for vitamin D deficiency calculated by linear discriminant analysis. RESULTS The mean serum 25-hydroxyvitamin D level was 19.8 ± 11.1, with 54% of the study population having vitamin D deficiency. This mean 25-hydroxyvitamin D level was lower than that observed historically in healthy controls, and was either similar or lower than in all but one representative historical cohort formed on the basis of chronic nonspecific musculoskeletal pain. Risk factors for vitamin D deficiency were black ethnicity, age < 60 years, and obesity. These risk factors were identified both in the entire cohort and separately in subgroups with and without obstructive sleep apnea. The biomarker (based on race, age, and body mass index) had a sensitivity and specificity for predicting vitamin D deficiency of 0.73 and 0.74, respectively. CONCLUSION Vitamin D deficiency was prevalent in patients with sleep disorders and chronic nonspecific musculoskeletal pain on evaluation in a sleep medicine clinic. Vitamin D deficiency was reliably estimated in the study population using a biomarker derived from common demographic characteristics.