Sleep apnoea severity independently predicts glycaemic health in non- diabetic subjects: the ESADA study

Sleep disordered breathing and dysglycaemia are intimately linked, but the existence of an independent relationship between them, beyond their shared association with obesity, has been difficult to definitively identify. In the largest reported study on this topic to date, we found OSA severity to be an independent predictor of glycaemic health, adding to a growing body of evidence that OSA has an independent

association with insulin resistance and impaired glucose tolerance.

The key finding of the present study is the independent relationship seen between OSA severity indices and HbA1c levels in non-diabetic subjects, which remains significant after adjustment for confounding variables. While prior data from the Sleep Heart Health Study and other reports have demonstrated a detrimental effect of sleep disordered breathing on other measures of insulin resistance, we evaluated a marker

that is a validated predictor of long-term cardiovascular morbidity and mortality in both diabetic and non-diabetic populations. Therefore, the independent relationship seen between HbA1c levels and sleep disordered breathing severity in this cohort suggests an increased future burden of cardiovascular disease in patients with more severe OSA and more significant nocturnal hypoxaemia.

We observed a significant, if modest, 0.25% difference in adjusted mean HbA1c between subjects in the mildest AHI quartile and those in the most severe quartile. The best data on the relationship of HbA1c levels with long-term outcomes in non-diabetic subjects is probably provided by the Atherosclerosis Risk in the Community (ARIC) study [11]. In that cohort, subjects with an HbA1c at baseline between 5.5% and 6.0% had an 18% increased risk of death, a 23% increased risk of incident coronary artery disease and an 86%

increased risk of incident diabetes compared with those with an HbA1c of 5.0–5.5%, over a median followup time of 14 years. It is a little difficult to assess the 0.25% difference in adjusted mean HbA1c seen in our cohort in that context, but it is notable that the mildest and most severe AHI quartiles would fall into the two categories mentioned above. We would suggest, however, that the clear increased odds of the more severe OSA severity quartiles having an HbA1c level o6.0% is the most important finding in this regard, as the data from the ARIC study would indicate that these are the subjects at markedly higher risk of later adverse events.

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