Background: Decreased levels of serum 25(OH)D, i.e., the best indicator of vitamin D supply to the body, have been reported both in COPD and OSA patients, while continuous positive airway pressure (CPAP) therapy has been shown to improve hypovitaminosis D.

Aim: To evaluate the effect of CPAP treatment on serum 25(OH)D levels in patients with coexistent COPD-OSA overlap syndrome (OS).

Methods: In consecutive OS patients, (diagnosed with pulmonary function testing and polysomnography), serum 25(OH)D levels, Epworth sleepiness scale (ESS) score and COPD assessment test (CAT) score were measured at baseline and 12 months after CPAP treatment. Compliance to treatment was assessed from the data retrieved from the CPAP device.

Results: Overall, 46 patients (43 males, mean age 60.9 years, mean BMI 37.8±5.5 Kg/m2, GOLD stage B 43.5%) were included and evaluated over a 12-month period. Most of the patients (82.6%) had severe OSA. After 12 months, the majority of patients shifted from COPD GOLD stage B to stage A. After 12 months of treatment, an improvement was observed in apnea-hypopnea index (AHI) (from 41.1/h to 3.1/h, p<0.001), ESS score (from 9 to 3, p<0.001] and CAT score (from 9 to 5, p<0.001). In all patients, serum 25(OH)D levels increased after 12 months of CPAP (from 21.3±8.4 to 23.8±8.7 ng/ml, p=0.001). Those were higher in OS patients with good 12-month CPAP compliance compared to patients with poor compliance (25.8±7.6 versus 20.4±9.6 ng/ml, p = 0.038).

Conclusions: In a sample of OS patients, good compliance to CPAP treatment was proven to be associated with improvement in OSA and COPD indices, as well as with an increase in serum 25(OH)D levels.