Obesity and sleep apnoea

Obstructive Sleep Apnoea (OSA) is associated with a number of medical conditions, namely cardiovascular disease, hypertension, obesity, diabetes, and depression. This article looks at the relationship between OSA and Obesity.

Obesity and Obstructive Sleep Apnoea

First we should clear up what we mean by obesity. Obesity is often defined using the Body Mass Index (BMI). Your BMI is calculated as your weight, in kg, divided by the square of your height in metres (the later provides a crude measure of the surface area of your body). BMI is supposed to be a measure of the thickness of body fat over the surface of the body. It is obviously a measure that can misrepresent actual body fat thickness compared to more accurate measures such as using body fat callipers at various skin fold sites. For example, a body builder at the time of competition will have very low levels of fat but would measure, using BMI, as obese.

The following graphic illustrates the typical physical appearance associated with different BMI measures. A normal BMI is between 18.5 and 25. A BMI of 25-30 is classified as overweight and above 30 as obese.

More detail about BMI and obesity, as well as an online calculator can be found here at the Australian Department of Health (Obesity).

While BMI may not be a precise measure of body fat level for a particular individual it is a simple measure to calculate and this has made it easy to use in survey based research. In many studies BMI has been found to be strongly associated with the incidence of medical conditions such as cardiovascular disease and OSA (these are called co-morbidities at the Australian Health link).

The ABS National Health Survey of 2004-05 indicates that some 41% of males and 25% of females were classified as overweight (with a BMI of between 25 and 30). Proportions of obesity were 18% for males and 17% for females (BMI over 30). While the proportion of overweight adults has increased since 1995, obesity has seen the largest increase.

Obstructive Sleep Apnoea is closely associated with obesity. OSA occurs when breathing is halted during sleep. The obstruction is created in the upper throat, at the junction where the mouth and nose passages. Physiological factors such as throat/neck length and variation in the shape/plasticity of upper throat contribute to OSA as well as neuromuscular control. The later ensures that the upper throat area does not relax too much during sleep thereby retaining its shape and keeping the airway open. An overly relaxed upper throat area is what promotes vibration during breathing, otherwise called snoring, and also OSA.

OSA and AHI

OSA severity is usually measured by the Apnoea-Hypopnoea Index (AHI). This is the average number of apnoea or hypopnoea events per hour of sleep. Apnoea refers to events where breathing is stopped and hypopnoea refers to shallow or reduced breathing events. Both events are considered to have similarly negative effects and accordingly are combined into the one index measure. The direct impact of both is a reduction in blood oxygen levels and disrupted sleep. Normal adults have an AHI of 0-4, mild apnoea is 5-14, moderate is 15-29, and severe is an AHI of 30+.These have flow on effects to cardiovascular health (cardiovascular disease, high blood pressure, strokes) and daytime fatigue and sleepiness. The Re-awakening Australia study used an AHI of 15+ to define the incidence of OSA.

Obesity and the resulting additional fat deposits around the throat make the job of keeping the airway open during sleep even more difficult. To make matters worse, the onset of OSA can promote weight gain, which then feeds back into more severe OSA. It is suggested that a couple of factors are at work. Firstly, the sleepiness induced by OSA reduces physical activity, thereby promoting weight gain. Secondly, the sleepiness is thought to directly increase appetite (and according to one study an appetite for refined carbohydrates). The association between depression and OSA is likely to further complicate the appetite and obesity relationship. There is also evidence of a link between diabetes and OSA, but untangling the contribution of obesity versus OSA when they often go hand in hand is difficult.

Health benefits from weight loss

If you are overweight or obese the health benefits from sustained weight reduction are clear and long lasting regardless of whether you have OSA or not. If you are overweight and experiencing the symptoms of OSA then it is important to see your Doctor and seek a proper diagnosis. Studies suggest that OSA symptoms are responsive to weight reduction. This article argues that treating OSA can help reinforce weight reduction efforts. With both reduced OSA and reduced weight the feedback mechanism can work for your benefit.

The interaction between obesity and OSA is a little complex. However, the advice to take from this article is quite simple. If you are overweight the health benefits from sustained weight reduction and management are significant and life enhancing. Among those benefits is a reduction in the risk of developing OSA. If you show any of the symptoms of OSA then there are clear health benefits from seeking proper diagnosis and treatment. OSA may be “feeding” your weight gain and consequently contributing to the severity of your OSA. If you (or your partner) suspect symptoms of OSA or if you are overweight, in either case the first step is to see your Doctor and set a course for better health.

Symptoms of OSA

The following are symptoms or indicators of OSA: Waking tired, restless sleep and waking during the night, daytime fatigue and irritability. OSA can sometimes be easier to detect by bed partners, family, or friends. Loud snoring, gasping and gulping for air and choking are common indicators of OSA. Other practices and symptoms associated with OSA include breathing through the mouth when sleeping, sleeping on your back, morning headache and/or dry mouth.

Aside from the references linked directly in this article additional sources were “Re-awakening Australia 2010” by Deloitte Access Economics, and “Interactions Between Obesity and Obstructive Sleep Apnea” by Abel Romero-Corral, MD, MSc, Sean M. Caples, DO, Francisco Lopez-Jimenez, MD, MSc, and Virend K. Somers, MD, PhD, FCCP. Obesity and Apnea. Note that Apnoea is the English spelling, and Apnea is the American spelling. Our articles use Apnoea except when referring to the title of a reference.