Who knew that diabetes and obstructive sleep apnea (OSA) could be related? People who have both do, and are probably the most compliant with continuous positive airway pressure (CPAP) therapy because they know its benefit to both conditions.
Consider this: Diabetes is a worldwide epidemic. Meanwhile, sleep-disordered breathing often remains undiagnosed and, therefore, untreated. A correlation between both conditions is not surprising, as today's research confirms.
Which Came First: OSA or Diabetes?
Researchers have known about this relationship for more than two decades. A key study led by Rees in 1981 reported the high incidence of sleep breathing disorders in diabetics. Many studies since then have shown independent associations between sleep apnea, glucose intolerance and insulin resistance. Today, insulin resistance is a well-known risk factor for diabetes.
But can one cause the other?It's complicated. Having diabetes could cause sleep breathing problems. Having OSA can lead to diabetes. Many diabetics are also obese, and obesity itself can lead to OSA. On the other hand, a person may not be diabetic at all, or live in a pre-diabetic state, and they may not even be obese. Should that person develop OSA, they are more likely to also develop diabetes if they don't treat their OSA.
What Statistics Show
According to Dr. Osama Hamdy, director at the Inpatient Diabetes Program at Boston's Joslin Diabetes Center, OSA affects about half of all diabetics. A 2014 study in the American Journal of Respiratory and Critical Care Medicine shows that for non-diabetics, 1 in 3 patients with severe OSA will also develop diabetes. Other studies show that when the severity of OSA increases, insulin resistance and glucose intolerance increase as well.
However, the relationship between sleep-disordered breathing and glucose, fasting insulin and hemoglobin A1c levels has been shown to be significant independent of the presence of obesity. A lean individual can have OSA and can also suffer from lower insulin sensitivity, so obesity alone cannot be the only culprit.
Diabetes and Sleep: Why Diabetics Have Trouble Sleeping
Diabetics have poorer sleep than the general population even when they have no identifiable sleep disorders. They experience high glucose levels at night which cause the kidneys to excrete excess sugar. This means multiple trips to the bathroom and disrupted sleep.
Diabetics also struggle to maintain balances in the hormone melatonin, which not only regulates the sleep-wake cycle, but also the release of insulin from the pancreas to regulate blood sugar. These imbalances can lead to insulin resistance, making glucose-insulin ratios difficult to control. In one major study, subjects who secreted the least melatonin at night were found to have double the risk for developing diabetes.
Diabetics also struggle with leptin resistance, which destabilize breathing patterns during sleep and depresses respiratory function. This may potentially explain why diabetics are predisposed to OSA.
Can OSA Cause Diabetes?
The body consists of a sophisticated collection of chemicals which are influenced by mechanics and neurology. When the body's chemistry strikes an imbalance, this shift in hormones can lead to systemic problems, especially if the shift takes place over a long period of time.
When a person has OSA, their upper airway is blocked by tissues which essentially cut off the air supply for ten seconds, often longer. This lapse in breathing shortchanges the bloodstream the oxygen it needs to deliver to the rest of the body.
When blood runs low on oxygen, the body experiences hypoxia. The brain, noting this hypoxia, sends chemical messages to the body to urge the lungs and diaphragm to breathe. When the obstructed airway prevents this, the brain sends a flood of stress hormones to the bloodstream to waken the person so they will consciously take the breath they need to restore oxygen.
When a person undergoes multiple lapses in breathing with awakenings all night long, for weeks and months at a time, this constant system correction leads to elevated blood sugar levels and impaired insulin sensitivity. Like a line of falling dominoes, unchecked insulin sensitivity leads to protracted insulin resistance, which then leads to glucose intolerance, and diabetes results.
Having OSA does not automatically guarantee a future diagnosis of diabetes, but studies continue to show its risk factors increase for those with untreated OSA.
Obesity, OSA and Diabetes
Weight gain is a common problem for both diabetics and people with OSA.
People with OSA gain weight due to chemistry imbalances. Ghrelin, the hormone which increases appetite, increases in people who suffer from OSA's sleep fragmentation. This leads to cravings of high-fat, high-carbohydrate foods to stave off daytime fatigue.
Leptin, ghrelin's counterpart, typically signals when the body is full, but people with OSA have decreased leptin and are shortchanged this critical metabolic regulator. These imbalances lead to behaviors that spawn overeating that, over time, can lead to obesity.
Consider this second domino effect: The excess tissue around the neck―due to being overweight―further aggravates OSA. This leads to a new set of chemical imbalances, which can eventually trigger diabetes.
Is CPAP the Answer?
It promises to be a useful intervention, if indirectly. Treatment of OSA by CPAP has been shown to improve insulin sensitivity in all patients who use it. In some cases, it has been shown to reverse insulin resistance. A recent study testing hemoglobin A1c levels before and after CPAP treatment showed significant improvements in blood sugar levels which positively corresponded with using CPAP at least 4 hours nightly for several consecutive weeks.
Diabetics should be vigilant about any snoring or suspected sleep breathing disorder. Active treatment of OSA with CPAP is shown to decrease and stabilize blood sugar levels in diabetics, especially those with moderate to severe OSA.
But what's even more crucial is identifying untreated OSA first. Screening for both sleep apnea and diabetes at the primary care level can help many patients identify and treat both conditions simultaneously. Using CPAP may delay or even prevent a nondiabetic patient from progressing on to diabetes, but keep in mind: CPAP cannot be prescribed without first confirming a sleep-breathing disorder like OSA via a sleep study.