Obstructive sleep apnoea (OSA) is a subcategory of sleep apnoea that is characterised by cycles of cessation to breathing that can last up to 30 seconds or more. The pauses to the breathing result in reductions in the saturation of oxygen tissue levels. Development of obstructive sleep apnoea is associated with an increased risk of cardiovascular disease and mortality. In particular the development of obstructive sleep apnoea may be an independent risk factor for the development of high blood pressure. Evidence suggests that being centrally obese, as characterised by the metabolic syndrome, increases the risk of obstructive sleep apnoea. The fact that the metabolic syndrome is characterised and likely caused by the development of insulin resistance suggests that insulin resistance may in some way be a causative factor in the development of obstructive sleep apnoea. In addition, the stress of obstructive sleep apnoea has been postulated to contribute to the development of insulin resistance.
Studies have investigated the relationship between insulin and sleep disordered breathing. For example in one study researchers made measurements of the fasting insulin plasma concentrations and the insulin resistance index using the homeostasis model assessment method (HOMA-IR) to assess the insulin function in 270 the subjects1. Subjects were free of diabetes, but 190 participants had been clinically diagnosed with obstructive sleep apnoea. The results of the study showed that subjects with obstructive sleep apnoea were more insulin resistant than subjects free of the disorder. This was indicated by higher measurements of fasting plasma insulin concentrations and higher HOMA-IR in the sleep apnoea diagnosed subjects. Although obesity was the strongest determinant of the presence of insulin resistance, sleep apnoea was independently associated with insulin resistance. The association between sleep apnea and insulin resistance was seen in both the obese and nonobese.
Therefore the presence of sleep apnoea predicts the concomitant presence of insulin resistance. Interestingly the authors of this study also investigated the association between insulin resistance and high blood pressure and confirmed previous observations that the two conditions are associated. It is difficult to state whether insulin resistance is the cause of obstructive sleep apnoea or if obstructive sleep apnoea is a contributory cause of insulin resistance. Mechanistically the formation of insulin resistance is well described and involves elevated production of fatty acids which accumulate in tissues and interfere with insulin signal transduction. To contribute to insulin resistance, obstructive sleep apnoea would have to contribute to this process, but to date explanations have been circumstantial and speculative. Therefore it is more likely that insulin resistance leads to the formation of sleep apnoea, something which is supported by the fact that the condition is more prevalent in the obese.
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