Indoor Employment as a Factor Associated with Vitamin D Levels in Obstructive Sleep Apnoea Syndrome

Background and Objectives: Variations in serum 25-hydroxyvitamin D [25(OH)D] concentrations have been described among individuals working in different settings. Moreover, published evidence suggests an association between Obstructive Sleep Apnea Syndrome (OSAS) and 25(OH)D insufficiency. The aim of this study was to assess the association between certain exposures in the occupational environment and 25(OH)D levels, in relation to OSAS severity. Materials and Methods: For a period of 12 months, 25(OH)D serum levels were assessed in subjects consecutively investigated for OSAS. These were divided into group A (control subjects working indoors), group B (control subjects working outdoors), group C (OSAS patients working indoors) and group D (OSAS patients working outdoors). Results: A total of 189 subjects were included (155 males and 34 females), comprising 129 OSAS patients and 60 non-apnoeic controls. Serum 25(OH)D levels were significantly higher in group B compared to the other groups (32 ± 13 vs. 23 ± 7 ng/mL for group A, p = 0.001; vs. 15 ± 8 ng/mL for group C, p < 0.001; and vs. 23 ± 9 ng/mL for group D, p < 0.001). Additionally, serum 25(OH)D levels were higher in group A compared with group C (23 ± 7 vs. 15 ± 8 ng/mL, p = 0.001), while no significant difference was observed between groups A and D (p > 0.05). Regression analysis revealed that the apnoea–hypopnoea index (β = 0.02, OR = 1.02, 95% CI: 1.00–1.04, p = 0.02) and indoor occupation (β = 1.03, OR = 2.80, 95% CI: 1.17–6.70, p = 0.02) were independently associated with vitamin D insufficiency. Conclusions: Serum 25(OH)D levels are decreased in OSAS patients working indoors. Thus, the working environment should also be considered in the overall assessment of 25(OH)D status in OSAS patients.