Obstructive sleep apnea is part of the spectrum of sleep-related breathing disorders that range from benign snoring to severe obesity hypoventilation syndrome. The association of abnormal sleep with daytime sleepiness is termed “obstructive sleep apnea syndrome” and is the main focus of this article.
Obstructive sleep apnea syndrome is very common and it is well recognized that it is associated with obesity; however, its strong relationship with diabetes is less well appreciated by clinicians, despite a report highlighting this from the International Diabetes Federation 10 years ago [1, 2].
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Sleep apnea is part of the spectrum of sleep disordered breathing disorders.
Epidemiology of obstructive sleep apnea syndrome
Epidemiological studies have shown that obstructive sleep apnea syndrome:
- affects between 6% and 13% of the adult population;
- is more common in men than women; and
- is common in those who are obese [3].
Obstructive sleep apnea syndrome causes daytime sleepiness, which significantly affects quality of life, work productivity, and increases the risk of accidents. Importantly, obstructive sleep apnea syndrome is also associated with an increased risk of metabolic syndrome and its consequences, which include ischemic heart disease and stroke, over and above the risks already associated with concomitant obesity.
Obstructive sleep apnea syndrome is also a risk factor for type 2 diabetes, with recent studies from Finland and the USA showing an increased risk of 1.5–2-fold [4,5]. A study from Oxford in the UK found that 23% of patients with diabetes had obstructive sleep apnea syndrome [6]; some other studies, for example LookAHEAD, have suggested an even higher prevalence of 80%, although this included people with less severe forms of obstructive sleep apnea, which may not all warrant treatment [7].
Why is obstructive sleep apnea associated with diabetes?
Potential mechanisms that might explain these associations include intermittent hypoxia and sleep fragmentation, which may:
- increase sympathetic activity;
- activate the hypothalamic–pituitary–adrenal axis; and
- increase oxidative stress and trigger inflammatory responses.
Some studies have found that obstructive sleep apnea syndrome may also be more common in people with type 1 diabetes, even in those who are not obese [8]. The mechanisms involved here are not known, but could possibly be related to the development of autonomic neuropathy. Cross-sectional observational studies have also shown higher prevalence of microvascular complications of diabetes, in particular higher rates of retinopathy and neuropathy in patients with obstructive sleep apnea syndrome and type 2 diabetes [9, 10], and more recently with poor healing of foot ulcers [11].
How to identify possible obstructive sleep apnea syndrome in the diabetes clinic
The diagnosis of obstructive sleep apnea syndrome should be suspected in patients with diabetes who report excessive daytime sleepiness; this can be assessed in clinic using the Epworth Sleepiness Scale [12]. The STOP-BANG questionnaire, which includes blood pressure, neck circumference, and BMI as markers of risk, is also useful [10]. Those scoring above 10 on the Epworth Scale, or 3 or above on the STOP-BANG questionnaire, should be referred for a sleep study; this is usually done as an overnight study at home using portable equipment that records pulse oximetry, breathing (either with airflow or a chest band) and an electrocardiogram trace. The data will be assessed in the sleep lab, and the key output is the apnea-hypopnea index, calculated by dividing the number of apnea events by the number of hours of sleep.
| The apnea-hypopnea index [13]. | |
| Normal | AHI <5 |
| Mild | AHI 5–14 per hour |
| Moderate | AHI 15–30 per hour |
| Severe | AHI >30 per hour |
| AHI=apnea-hypopnea index | |
Most guidelines recommend offering continuous positive airway pressure (CPAP) treatment to those with an apnea-hypopnea index of 15 or above who have evidence of daytime sleepiness [11].
Treatment of obstructive sleep apnea syndrome
Treatment of the symptoms of obstructive sleep apnea syndrome, especially daytime sleepiness, should include advice about adopting regular sleeping habits as much as possible. Those who are obese should be supported in efforts to lose weight, as weight loss can improve symptoms; this has been shown with dietary weight loss, the glucagon-like peptide-1 receptor agonist liraglutide at the approved dose for obesity (3 mg daily), and with bariatric surgery [14–16]. Most people with obstructive sleep apnea syndrome and daytime sleepiness will also be offered a trial of CPAP, which helps to maintain airway patency during sleep and prevents the intermittent hypoxia and subsequent arousals from sleep that result in daytime sleepiness. Other treatments that are less effective, but preferred by some, include airway splints and surgical approaches such as uvulopalatoplasty.
There is no question that CPAP is an effective intervention that improves sleep quality and thus reduces daytime sleepiness in people with obstructive sleep apnea syndrome. However, it has been more difficult to convincingly demonstrate metabolic benefits, despite the strong epidemiological associations, and uncontrolled observational studies suggesting benefit [17]. Randomized controlled trials using “sham” CPAP are generally of short duration for ethical reasons. Those that have been conducted have consistently shown small reductions in blood pressure, but no changes in glucose metabolism, markers of insulin resistance, or metabolic syndrome [18, 19].
Conclusion
In summary, obstructive sleep apnea is commonly associated with type 2 diabetes and its presence appears to be associated with a higher risk of complications. Treatment includes weight loss and use of CPAP; the latter will be most effective at controlling symptoms of daytime sleepiness, but glucose control and other risk factors should be managed according to standard guidelines.