Mr. Jones has been struggling with his weight for years.  No matter what diet he has tried, he has never been able to reach his goal weight.  Even if he is able to lose a few pounds, he just can’t seem to keep the weight off.  He has never been one to exercise even though he knows it would probably help with weight loss.  By the time he gets home, he feels too exhausted to exercise.  Even a short walk seems like an insurmountable chore.  Six months ago, his physician told him that he had type II diabetes and started him on medication to bring down his blood sugar.  Last week he also discovered he has sleep apnea.  He feels frustrated and discouraged about having “so many medical problems.”  He recently read an article about the relationship between weight and sleep apnea and is wondering if the apnea may have caused his weight problem.  He asks his doctor if using PAP therapy will help him to lose weight and improve his blood sugar.

Multiple studies show that being overweight is the strongest risk factor for developing obstructive sleep apnea (OSA).  However, there is now evidence to suggest that OSA itself may influence whether an individual develops weight problems and type II diabetes.  Recent studies show a link between OSA and abnormal metabolism of blood sugar.  Body cells can become resistant to the action of the sugar-regulating hormone insulin, a condition known as insulin resistance.  Insulin resistance occurs more commonly in patients with OSA and is an early step in the development of type II diabetes.  The link between OSA and insulin resistance is important as it may point to OSA as a risk factor for the development of type II diabetes and obesity.  For many people with OSA, it raises the interesting question of treating OSA to improve blood sugar control and help with weight loss.
 

Understanding insulin resistance
The exact link between OSA and insulin resistance remains unclear but is likely to involve multiple complex processes.  Under normal conditions, insulin is released in response to the ingestion of glucose (sugar) in the form of food.  Insulin functions like a key that allows cells to open, take glucose out of the blood and use it for energy.  Insulin’s main job is to keep the level of sugar in the blood within safe levels.  Insulin resistance occurs when the cells require higher amounts of insulin in order to let in the same amount of glucose.  Insulin resistance also raises blood sugar levels.  The glucose-using cells become immune to the action of insulin and insulin-producing cells produce excessive amounts of insulin.  High levels of insulin and blood sugar result in weight gain and further difficulties with glucose metabolism. 

OSA and insulin resistance
In OSA, airway closure causes breathing to stop and oxygen levels to drop.  This stresses the body and causes the release of stress hormones.  These stress hormones elevate blood glucose levels many times each night and cause the production of high levels of insulin.  As we have already learned, high insulin levels result in weight gain.  People who feel sleepy and fatigued from OSA don’t exercise as much, making them more likely to gain weight and further increasing the chance of developing insulin resistance. Obesity and insulin resistance can progress to type II diabetes.  Conversely, insulin resistance and type II diabetes contribute to additional weight gain and worsening OSA.  The relationship between weight, type II diabetes, and OSA seems to be a vicious cycle.

Two large, well-documented studies support the link between OSA and insulin resistance.  The first study, by Ip and colleagues (2002), followed 270 people referred for sleep studies who did not have diabetes.  They discovered that the severity of OSA was associated with insulin resistance.  That is, the worse the apnea, the more likely the person was to have high levels of insulin and blood sugar.  This association between OSA and insulin resistance was seen in both obese and non-obese subjects.

Data from the Sleep Heart Health Study (Punjabi et al, 2004) further support the relationship between OSA and insulin resistance.  This large study also showed that OSA is associated with abnormal glucose metabolism and insulin resistance even when other contributing factors such as age, gender, smoking, weight, waist size, and amount of sleep each night are taken into account.  As in the study by Ip and colleagues, the more severe the OSA, the more likely the person was to develop insulin resistance.

Will PAP therapy help with weight loss and blood sugar control?
Early studies did not show that treatment of OSA with CPAP therapy improved insulin and glucose regulation.  However, in most of these studies people used CPAP for only a short period of time, from only one night to a maximum of 6 months.  It is possible that since it takes many years for insulin resistance to develop into diabetes, recovery may also take a long time.  Still, some studies show promise that treatment of OSA may improve insulin resistance.  A study published recently by Babu and colleagues (2005) demonstrated that CPAP use improved blood sugar control in very obese individuals with type II diabetes.  Importantly, a strong relationship was seen between blood sugar control and adherence to CPAP therapy.  Specifically, there was a greater improvement in glucose levels in those individuals using CPAP for more than four hours per night.

During his first visit to the sleep clinic, Mr. Jones discusses his concerns about his diabetes and weight gain with his physician.  While the exact nature of the relationship between diabetes, weight, and OSA is not fully understood, there is currently enough evidence to suggest a strong relationship between OSA, diabetes, and obesity and that treatment of OSA may improve glucose metabolism and prevent further weight gain.  While many individuals may experience a dramatic response to complaints of fatigue, sleepiness, and sleep disturbance, improvement in blood sugar and impact on weight may take several months or longer.  Consistent nightly use of PAP therapy should result in improvement in energy levels that may motivate the individual to increase activity and exercise.  Exercise clearly plays a key role in weight loss and improved blood sugar control.  For these reasons alone it is worthwhile to work aggressively at accepting and adhering to PAP therapy.