For instance, in 2012, Bozkurt et al. [41] reported a significant negative association between serum 25(OH)D levels and glucose metabolism indices (fasting glucose, insulin, and HOMA-IR), as well as the prevalence of prediabetes and diabetes mellitus, assessed through a 75-g oral glucose tolerance test, among 143 patients with OSA. This evidence concerns the gene INS and obstructive sleep apnea syndrome.