Sleep Apnea, Cortisol Levels, & Glucose Metabolism

Obstructive sleep apnea (OSA) has been linked to several health risks, including increased risk of hypertension and excessive daytime sleepiness, which can increase the risk of motor vehicle accidents and occupational accidents. According to research cited in the article, there is growing evidence that OSA is connected to glucose intolerance, insulin resistance, and type 2 diabetes. “Several recent studies have shown that the prevalence of altered glucose metabolism and type 2 diabetes are increased in OSA patients, independent of age and central obesity.”

Researchers at the University of Split School of Medicine, Split, Croatia created a study to examine the relationship of hypothalamic-pituitary-adrenal (HPA) activity and glucose metabolism in severe and moderate OSA.

“The role of HPA axis in glucose metabolism alterations is, however, still largely debated since OSA features numerous pathophysiological mechanisms that can interfere with glucose metabolism. Therefore, in this study, we tried to integrate the relationship of HPA axis and glucose metabolism in OSA patients.”

Newly diagnosed OSA patients at the Split Sleep Medicine Center were recruited between June 2013 and December 2014. Female patients were excluded, as were those diagnosed with diabetes, severe cardiovascular, psychiatric, neurological, respiratory, or renal disease and active malignant disease. Patients were also excluded due to regular use of drugs that could interfere with glucose metabolism or HPA axis, sedatives or narcotics, and alcohol or drug abuse or if they had a history of OSA treatment prior to study enrollment.

The moderate OSA group (24 patients) and severe OSA group (32 patients) were matched with 20 healthy male controls based on age and BMI. All groups underwent a detailed medical history, physical exam, and anthropometric measurements. Only the OSA groups participated in full-night polysomnography.

One to two weeks after the sleep studies were performed, all groups underwent laboratory testing of morning plasma cortisol, fasting plasma insulin, and fasting plasma glucose.

Results were as follows:

• Morning plasma levels lower in severe OSA group compared to moderate OSA and control groups

• Morning plasma levels similar between moderate OSA and control groups

• Respiratory variables significantly inversely correlated with morning plasma cortisol levels

• Glucose metabolism impaired in both severe and moderate OSA groups, but more pronounced in severe OSA group

• Prevalence of prediabetes was 59.4% in severe OSA group and 41.7% in moderate OSA group

According to the authors, “It is important to highlight that pathophysiological mechanisms of insulin resistance and glucose metabolism alterations in OSA are of complex nature and cannot be approached linearly. This state could arise due to the fact that patients with OSA usually exhibit nocturnal hypercortisolism, and this dynamic might be responsible, at least partially, for the negative effects on glucose metabolism.”

The authors noted several limitations of their study. A larger sample size, especially in the severe OSA group would contribute to findings, and the inclusion of female patients would allow results to apply to the whole OSA population. They also suggested a 24-hour cortisol profile instead of measuring levels at a single point in time, which did “not allow studying the precise alterations and dynamics of cortisol levels.”

Reference: Bozic J, et al. Morning cortisol levels and glucose metabolism parameters in moderate and severe obstructive sleep apnea patients. Endocrine. 2016 Mar 21. [Epub ahead of print]