Investigating the Relationship between Sleep Disordered Breathing, Glycaemic Control and Inflammation

Metabolic Syndrome (MetS), Type 2 Diabetes (T2DM) and obesity related sleep disorders like Sleep Disordered Breathing (SDB) share common features including visceral adiposity, impaired glycaemic control and increased cardiovascular disease (CVD) risk. As sub-clinical inflammation is considered a key player in these conditions they are thought to be interrelated. We aimed to further investigate this putative interrelationship. In a multi-ethnic population with a spectrum of glucose tolerance (sub-study of the ADDITION-study), we report that abdominal obesity underpins the association between SDB and systemic inflammation. South Asians with SDB had significantly higher levels of leptin, poorer glycaemic control but lower levels of oxidative stress than their Caucasian counterparts. These data suggest that the pathogenesis of SDB is different between these ethnic groups and may aid in understanding why South Asians are at increased risk of T2DM and CVD. Furthermore, SDB is independently associated with increased likelihood of MetS. However, no differences in cardiovascular markers, inflammatory biomarkers or anthropometric measures were observed between those with excessive daytime sleepiness or sleep disturbances as determined by the Epworth Sleepiness Scale and the Sleep Assessment Questionnaire, respectively. This suggests that these questionnaires are broad and insensive in identifying these sleep parameters. Obstructive Sleep Apnoea (OSA) is a severe form of SDB which can be successfully treated with Continuous Positive Airway Pressure (CPAP). Reported results on the effects of CPAP therapy on glycaemic control are inconsistent thus no difinative conclusion could be made from the systematic review carried out to answer this research question. Thus 'The Leicester Sleep and Sugar Study' was conducted to further establish whether CPAP-therapy impacts glycaemic control or systemic inflammation in subjects with established T2DM and newly diagnosed OSA. We report a clinically significant improvement in glycaemic control (HbA1c -0.8%) and a significant reduction in waist circumference with improved psychological well being 6 months post CPAP-therapy. It is evident that OSA is associated with T2DM and MetS although the direction of cause and effect has not been elucidated to date. The results reported here suggest that OSA negatively impacts on glycaemic control. Additionally we report a possible ethnic difference in the pathophysiology of SDB with inflammation playing a key role. Further research is required in this area to further establish these findings.