The link, or part of it, may be due to the fact that sleep apnea and diabetes share some risk factors. Obesity and cardiovascular disease are related to both conditions. Sleep apnea doesn’t just increase the likelihood of developing cardiovascular disease -- heart problems can also lead to sleep apnea. Also, people who have diabetes are at least twice as likely to develop heart disease,according to the National Institute of Diabetes and Digestive and Kidney Diseases. 

  Obesity is another known risk factor for heart disease, but in addition, a study of 306 obese patients with diabetes found that a stunning 86 percent of them also had undiagnosed sleep apnea. These conditions all appear to be related. 

  Experts do have some indications of what biological mechanisms might be behind this connection, based on how sleep apnea affects the body.

  "There are two main consequences of sleep apnea during the night," says Gagnadoux. He points to hypoxemia, or times when the concentration of oxygen in the blood dips to below normal levels, and sleep fragmentation. "We know from animal studies that both are risk factors for developing insulin resistance," he adds.

  Hypoxemia can set off a chain reaction in the body that leads to impaired glucose tolerance and increased oxidative stress, which means the body has an excess amount of molecules called reactive oxygen species. These molecules can disrupt the body’s ability to repair itself. The whole process can also contribute to insulin resistance.

  Sleep fragmentation of any sort can push a person's body into state of stress and cause the release of cortisol, a hormone that can strongly alter the metabolism. Repeated awakenings can also lead to insulin resistance, a greater appetite and the craving for carbohydrates. Diabetes gets its foot in the door with all these changes. Higher sleep variability has even been linked to problems with controlling the amount of glucose in the blood. “The more severe the apnea, the more disturbed a patient’s glucose control,” says Mostafavi.