From the author:

In response to our recent article on sleep, sleep-disordered breathing and metabolism 1, P. Steiropoulos and co-workers wish to emphasise the role of adherence to continuous positive airway pressure (CPAP) treatment in improving obstructive sleep apnoea (OSA) metabolic status. This is certainly a major factor of success regarding CPAP treatment effectiveness. Whilst CPAP compliance remains a major challenge 2, the optimal duration of treatment remains unclear. It has been suggested that improving vigilance and cognitive function would need a minimum of 5 h, apparently with additional benefits when the duration of treatment was further increased 3. This is much less clear as regard cardiovascular and metabolic changes. There is apparently a relationship between CPAP duration and reduction in blood pressure 4. There is very limited evidence regarding CPAP effects on glycaemic control. P. Steiropoulos and co-workers noticed that mean CPAP use in the two randomised control trials was <4 h, 3.6 5 and 3.9 h 6, respectively. Thus, they question whether insufficient CPAP use may be a potential confounding factor in the published negative findings. They have recently demonstrated that CPAP use for >4 h per night is crucial in ameliorating HbA_1c and total cholesterol levels along with several inflammation markers after 6 months of CPAP treatment in non-diabetic OSA patients, with only adherent patients exhibiting beneficial metabolic effect 7. They also recently reported that only patients using CPAP for >4 h had significant reduction in soluble and cellular immune response factors 8. Their study on glycaemic control 7 is not a randomised controlled trial and as such has significant limitations. Moreover, good adherence to long-term CPAP treatment seems to significantly reduce HbA_1C levels but has no effect on markers of insulin resistance 7. The study by Harsch et al. 9 did not shown any effect on insulin sensitivity in OSA patients with a body mass index >30 kg·m⁻². In this study, the mean compliance to CPAP was high, i.e. 5.2±0.91 h 9. In addition, there was no association between mean duration of CPAP use per night and change in insulin sensitivity from baseline to 3 months 9. Insulin resistance and glycaemia are closely linked in obesity and diabetes pathophysiology. Thus, it may be concluded that CPAP compliance is certainly an important issue. However, obesity is a major confounding factor in OSA. Thus, it is not surprising that CPAP effects on glycaemic control could be modulated by the degree of obesity. It should certainly be further studied by large randomised controlled trials 10, 11.

Statement of interest

None declared.