The role of vitamin D in obstructive sleep apnoea syndrome

Obstructive sleep apnoea syndrome (OSAS) is a common disorder of multifactorial pathogenesis and is associated with obesity, diabetes and cardiovascular disease. Vitamin D is a fat-soluble vitamin with an important function in calcium absorption and homeostasis, which is also implicated in several nonskeletal conditions. The prevalence of vitamin D deficiency is increasing worldwide and is associated with similar metabolic disturbances to OSAS. Moreover, recent data suggest that in OSAS patients serum levels of vitamin D are lower compared with non-apnoeic subjects. However, the mechanisms linking vitamin D deficiency and OSAS are not completely understood and several hypotheses have been advanced. To date, a limited number of studies have assessed the association between lower serum concentrations of vitamin D and OSAS, and have reported inconsistent results. Similarly, contradictory results have been produced by studies which evaluated the effect of continuous positive airway pressure treatment on serum vitamin D levels. The aim of this review is to summarise current knowledge on the association between OSAS and vitamin D levels. KEY POINTS: Vitamin D insufficiency prevalence is increasing worldwide and presents with similar comorbidities and risk factors to OSAS. The nonskeletal actions of vitamin D may contribute to the development of OSAS through immune system modulation, myopathy and inflammation. Studies evaluating serum vitamin D concentrations in OSAS patients and the effect of CPAP treatment report contradictory results, often influenced by confounding factors, such as obesity. There appears to be potential for use of vitamin D supplementation in OSAS patients as a means of reducing the incidence of cardiovascular disease, a comorbidity common in both conditions. EDUCATIONAL AIMS: To assess the potential association between OSAS and serum levels of vitamin D. To discuss the pathogenetic mechanisms linking OSAS and vitamin D insufficiency. To illustrate the effect of CPAP treatment on vitamin D concentration in OSAS patients.