Previous studies have shown associations between diabetic retinopathy (DR) and obstructive sleep apnea (OSA), but the authors of a recent study wanted to take things a step further and evaluate longitudinal relations in larger cohorts.

This cross-sectional and five-year longitudinal study included 153,238 patients with type 2 diabetes who had attended diabetic eye screening and were registered in the Danish Registry of Diabetic Retinopathy (DiaBase). Each of these were matched by five controls without diabetes of the same age and gender.

Patients with type 2 diabetes were more likely to have prevalent OSA (odds ratio 2.01) and to develop OSA within five years. Type 2 diabetes patients with DR at baseline were less likely to have prevalent OSA (OR 0.57) and to develop incident OSA. Likewise, patients with OSA had a lower risk develop HR (HR 0.83, 95% CI 0.74-0.92).

Those with higher levels of DR were more likely to be male, have had a longer duration of diabetes, had a higher comorbidity index score and were more likely to use insulin and antihypertensive drugs. In contrast, a higher prevalence of OSA was found for all patients with a lower level of DR.

Patients screened for DR for the first time had twice the prevalence of OSA as age- and gender-matched persons without diabetes.

“Unexpectedly, the highest risk was identified in patients without DR, who, independently of other factors, had a 14% and 43% higher rate of prevalent and incident OSA, as compared to patients with DR,” the authors noted in their paper. “With the data at hand, we cannot know if this can be explained by pathophysiological mechanisms or if. This was a result of a potentially better awareness of diabetes and associated complications in those without DR, which could make these patients more likely to receive a hospital-based diagnosis for OSA.

“While we would not expect OSA to be a casual protector of DR from a pathophysiological point of view, our results could indicate that patients with OSA might have obtained a better understanding of diabetic complications and measurements for avoidance, like improved glycemic control, blood pressure lowering and better management of dyslipidemia."

The study concludes patients with type 2 diabetes were twice as likely to have OSA, with the highest risk identified in those without DR. Patients with type 2 diabetes were also more than 50% as likely to develop OSA within five years, but DR and OSA were inversely linked with a lower risk for each other.

The authors noted limitations to this study, such as some factors like obesity being underreported in registries and potential inaccuracies in coding practice in register-based studies.