"There are many studies published during the last five to ten years showing a strong link between sleep apnea and diabetes, especially type 2 diabetes," says Frédéric Gagnadoux, a professor of medicine at the University of Angers and a respiratory physician who specializes in sleep disordered breathing. A 2012 review of the evidence linking the two conditions estimated that about 71 percent of people with type 2 diabetes may have sleep apnea, based on an average of five studies looking at a total of 1,200 patients^1.

  The link goes the other direction also.  A 2014 study looked at 6,616 people who participated in the European Sleep Apnea Cohort and looked to see how many had both sleep apnea and type 2 diabetes. 28.9% of those with severe apnea had diabetes, even when the researchers accounted for other risk factors such as obesity^2. In other words, just under a third of people with severe sleep apnea also had type 2 diabetes. 

  The researchers also found that people with more severe apnea were more likely to also have type 2 diabetes: The prevalence of diabetes varied according to how severe the sleep apnea was.  The conclusion of the study reads, “Increasing OSA severity is associated with increased likelihood of concomitant T2DM (type 2 diabetes mellitus) and worse diabetic control in patients with T2DM”.