We thank Harsch et al for their comments. Their letter highlights the important contribution of obesity in studies of both insulin resistance and obstructive sleep apnoea (OSA). Although obesity underlies both pathologies, it also confounds studies investigating these conditions. The only studies therefore that can determine conclusively the effect of continuous positive airway pressure (CPAP) on improvements in insulin resistance and glycaemia in patients with OSA are double blind randomised controlled trials. We agree that a randomised controlled trial of CPAP in less obese subjects with type 2 diabetes would clarify this area further, but a study of pre-diabetic subjects with insulin resistance would be even more enlightening.