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Sleep apnea - what is it, how common is it and how does it affect mortality & physical health?

Sleep apnea is a common, but frequently unrecognised, contributor to psychological difficulties and to health problems more generally.  I would like to look at a series of questions about this disorder - what is it, how common is it, why is it important, how do you recognise it, and what can be done about it?

What is sleep apnea?  Well trusty Wikipedia tells us that "Sleep apnea, also spelled sleep apnoea, is a sleep disorder characterized by pauses in breathing or instances of shallow breathing during sleep.  Each pause, called apnea, can last for a few seconds to several minutes.  For a diagnosis of sleep apnea, more than five episodes an hour must occur ... When breathing is paused, carbon dioxide builds up in the bloodstream. Chemoreceptors in the blood stream note the high carbon dioxide levels. The brain is signaled to wake the person sleeping and breathe in air. Breathing normally will restore oxygen levels and the person will fall asleep again ... an individual with sleep apnea is rarely aware of having difficulty breathing, even upon awakening.  Sleep apnea is recognized as a problem by others witnessing the individual during episodes or is suspected because of its effects on health or alertness. Symptoms may be present for years (or even decades) without recognition."

How common is it?  Young et al estimate that approximately 15% of US adults are affected by sleep apnea, with rates rising in parallel with increasing obesity.  More accurately, Peppard et al. performed a series of polysomnography studies repeated at 4 year intervals in a cohort of 1,520 US adults - "Increased prevalence of sleep-disordered breathing in adults" - and they reported that "The current prevalence estimates of moderate to severe sleep-disordered breathing (apnea-hypopnea index, measured as events/hour, >/=15) are 10% (95% confidence interval (CI): 7, 12) among 30-49-year-old men; 17% (95% CI: 15, 21) among 50-70-year-old men; 3% (95% CI: 2, 4) among 30-49-year-old women; and 9% (95% CI: 7, 11) among 50-70 year-old women. These estimated prevalence rates represent substantial increases over the last 2 decades (relative increases of between 14% and 55% depending on the subgroup)."  The US "National Sleep Foundationcomment that "There are a number of factors that increase risk, including having a small upper airway (or large tongue, tonsils or uvula), being overweight, having a recessed chin, small jaw or a large overbite, a large neck size (17 inches or greater in a man, or 16 inches or greater in a woman), smoking and alcohol use, being age 40 or older, and ethnicity (African-Americans, Pacific-Islanders and Hispanics). Also, OSA seems to run in some families, suggesting a possible genetic basis." and they also state "More than 18 million American adults have sleep apnea. It is very difficult at present to estimate the prevalence of childhood OSA because of widely varying monitoring techniques, but a minimum prevalence of 2 to 3% is likely, with prevalence as high as 10 to 20% in habitually snoring children. OSA occurs in all age groups." 

Why is it important?  Well basically because sleep apnea is associated with both increased mortality and increased rates of a whole series of physical and psychiatric diseases.  Young et al, in their 2008 paper "Sleep disordered breathing and mortality: eighteen-year follow-up of the Wisconsin sleep cohort" found a 50% increase in death rate for those with mild or moderate sleep apnea, and a three to four fold increased risk of death in those with severe sleep apnea - "All-cause mortality risk, adjusted for age, sex, BMI, and other factors was significantly increased with SDB severity. The adjusted hazard ratio (HR, 95% CI) for all-cause mortality with severe versus no SDB was 3.0 (1.4,6.3). After excluding persons who had used CPAP treatment (n = 126), the adjusted HR (95% CI) for all-cause mortality with severe versus no SDB was 3.8 (1.6,9.0); the adjusted HR (95% CI) for cardio-vascular mortality was 5.2 (1.4,19.2). Results were unchanged after accounting for daytime sleepiness. Conclusions: Our findings of a significant, high mortality risk with untreated SDB, independent of age, sex, and BMI underscore the need for heightened clinical recognition and treatment of SDB, indicated by frequent episodes of apnea and hypopnea, irrespective of symptoms of sleepiness."

What physical diseases is it associated with?  Obstructive sleep apnea is associated with increased rates of a whole series of major physical diseases including high blood pressure, coronary heart disease, stroke, type II diabetes, cancer, loss of cognitive function & full dementia, as well as - stretching the meaning of physical disease - increased risk of injury & death from road traffic accidents (RTA's).  Basoglu & Tasbakan in their 2014 paper "Elevated risk of sleepiness-related motor vehicle accidents in patients with obstructive sleep apnea syndrome: a case-control study" reported a doubling of RTA risk in OSA sufferers, with risk rising even further for those with increased neck circumference (43cm or more - note other studies have reported increasing OSA problems with thinner necks than this e.g. >17in for men & >16in for women) and those reporting higher levels of daytime sleepiness (scoring 11 or more on the Epworth Sleepiness Scale).  There is an extensive research literature on links between sleep apnea, high blood pressure and cardiovascular disease - see, for example, the 2008 American Heart Association's position paper "Sleep apnea and cardiovascular disease" and the more recent large prospective study "Association between treated and untreated obstructive sleep apnea and risk of hypertension".  In the Young et al study, mentioned in the previous paragraph, note that over 18 years follow-up, cardiovascular mortality occurred at over 5 times the rate in those with untreated severe sleep apnea (compared to those with no sleep disordered breathing).  Attention has also turned to the way sleep apnea increases risk of cancer as well - see last year's "Putative links between sleep apnea and cancer: from hypotheses to evolving evidence" - and for cognitive function & dementia, see "Sleep apnea and the risk of dementia: a population-based 5-year follow-up study in Taiwan" and the broader overview "Impact of sleep on the risk of cognitive decline and dementia".

Overall message so far:  Sleep apnea is a common, regularly unrecognised disorder, occurring in approaching 1 in 5 adults.  It becomes even more common with increasing weight and increasing age (so with our aging, fattening population, sleep apnea is becoming a more & more worrying issue).  Men are more likely to suffer from sleep apnea than women, and both alcohol & smoking tend to aggravate the problem.  It's important to realise though that sleep apnea can affect all age groups, including children.  Particularly as it becomes more severe, sleep apnea is linked with a wide range of severe diseases and with significantly increased death rates.  

In the next post I'll look at the relevance of sleep apnea for psychiatric disorders and, in the third post of this sequence, I'll discuss how it's recognised & what can be done about it. 


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