The link between sleep apnoea and obesity

Obesity is commonly defined via the body mass index (BMI). An adult’s BMI is calculated by dividing their weight in kilograms by their height in metres squared. The resulting figure can then be put into the following categories:

• Underweight: 18.5 and below
• Healthy weight: between 18.5 and 24.9
• Overweight: between 25 and 29.9
• Obesity: between 30 and 39.9
• Severe (also known as morbid) obesity: 40 or more

Do remember that body mass index is just one measure of health – for example if you have a lot of muscle (which weighs more than fat) you may fall into the overweight category despite not having much body fat. BMI ranges can also vary slightly for people of different ethnic backgrounds and are measured differently in children, so it’s a good idea to speak to your doctor if you’re concerned about your weight. They may use other measurements, such as waist circumference, to help determine whether you need to lose weight.

How common is obesity or being overweight?

Throughout the world, almost 10% of adults are living with obesity – that’s almost one in 10³ of the general population. And when it comes to the overweight category, the figures are even higher, with nearly one out of three³ adults having a body mass index between 25 and 29.9. So if you are carrying more weight than you’d like, you’re certainly not alone.

How common is sleep apnoea in people who are overweight?

The occurrence of sleep apnoea in the general population is thought to be around 25%⁴ – however, it’s estimated that more than 80% of sleep apnoea cases worldwide are yet to be diagnosed⁵, so it’s hard to pinpoint exact figures!

What we do know is that around 40% of people who are in the overweight category have sleep apnoea⁶. While this figure seems high, it’s worth bearing in mind that suggests 60% of overweight people don’t have sleep apnoea! In people with severe obesity, the percentage affected by sleep apnoea rises to 77⁶. To understand why a higher body weight seems to be a risk factor for sleep apnoea, it helps to know the causes of the condition…

With obstructive sleep apnoea it’s all connected to what is blocking the airways. In most cases it’s the muscles and soft tissues of the throat, which relax during sleep. If someone has nasal congestion, a naturally more narrow airway or other physical characteristics¹³, such as a big tongue or large tonsils, the airway is likely to get blocked more easily. It’s not hard to see how being overweight or obesity could exacerbate this further: when people gain weight, they gain it all over – including visceral or ‘hidden’ fat deposits within the throat area. This additional body fat can narrow the airways, particularly if you’re lying down. People who are overweight are also more likely to have a bigger neck circumference¹³, which is another risk factor for OSA.

Weight can also affect the severity of OSA, which is split into three categories:

• Mild: 5 to 14 apnoeas per hour
• Moderate: 15 to 30 apnoeas per hour
• Severe: more than 30 apnoeas per hour

As a general rule, the higher your BMI the more severe the sleep apnoea. If you have a BMI below 30, OSA is usually less severe – however these people still need attention, as they are four times more likely to develop high blood pressure than people in the obese category who don’t have OSA (see below for more on high blood pressure and OSA)¹⁴.

Mixed or central sleep apnoea and obesity

It’s worth noting that while obstructive sleep apnoea makes up 84% of sleep apnoea cases¹⁵, there are other forms that are less common:

• Central sleep apnoea: this occurs when the brain stops sending signals to the muscles that control breathing during sleep, so breathing stops for short periods. It doesn’t have anything to do with the airways being blocked – they remain open during sleep.
• Mixed sleep apnoea: as the name suggests, this is a combination of central and obstructive sleep apnoea.

Both these conditions are primarily caused by medical conditions affecting the brain, so aren’t associated with obesity.

As well as having a higher risk of developing OSA, people living with obesity and severe obesity are at risk of other breathing disorders too…

Obesity hypoventilation syndrome (OHS)

This condition is usually only seen in people with obesity or severe obesity. The risk of OHS rises with body mass index: almost half of people with a BMI of 50 or more have the condition²⁷ (for context, it’s projected that by 2030 nearly one in four people in the United States will have a BMI of more than 50²⁸).

OHS shares some of the same symptoms as OSA, such as daytime sleepiness and headaches, but can also cause difficulty breathing. Around 90% of OHS patients also have obstructive sleep apnoea^3,29, and often have other conditions at the same time, such as cardiovascular disease, with up to 88% having hypertension^3,30.

While OHS is a serious condition, there is treatment available, so if you think you may be at risk take a look at our obesity hypoventilation syndrome page and speak to your doctor.

Now we’ve looked at the negatives of sleep apnoea, here are some positives! There is lots that can be done help people with the conditions live happier, healthier lives. A treatment plan for someone with obesity and OSA might include a combination of the following:

• Lifestyle changes, including weight management (which could also be aided by medication)
• Continuous positive airway pressure (CPAP) therapy. This is considered the ‘gold standard’ treatment for OSA – more on this below!
• A mandibular advancement device (a small oral appliance, like a gumshield, worn in the mouth overnight)
• Surgery – in rare cases this may be considered if other treatments prove ineffective. It could take the form of either an operation to clear the airway of a physical blockage, or bariatric surgery (such as a gastric band or bypass) to aid weight loss.

CPAP therapy is a common and effective treatment for OSA. CPAP stands for continuous positive airway pressure, this is because a CPAP machine produces a steady flow of pressurised air that a person breathes in via a mask while they sleep. This pressured air helps to keep the airways open, preventing apnoeas and hopefully leading to a more refreshing night’s sleep.

The amount of air pressure required to keep your airways open is somewhat dependent on how many apnoeas you have in a night (ie the severity of your OSA). Lower levels of pressure are easier to get accustomed to and more comfortable, so anything that helps reduce the severity of your OSA at the same time as having CPAP (like weight loss) is a good thing.

You may be tempted to think that if you lost enough weight, you might be able to stop CPAP therapy altogether. However, while weight loss can help reduce the severity of OSA, it is unlikely to stop it completely (remember the results in people who’d had bariatric surgery?). So if you feel like your OSA symptoms have improved, it’s likely due to your weight loss in combination with the CPAP therapy – the two things are closely intertwined and it can be hard to tell what’s causing the other. For this reason, you should always speak to your doctor before stopping CPAP treatment. It’s likely they will encourage you to continue with a combined approach that benefits your whole health, rather than just your OSA.

Seeking help for obesity and OSA

Because of the connection between OSA and obesity, it’s recommended that people with a high BMI are tested for sleep apnoea. And as anyone can have the condition, no matter what their weight – if you’re experiencing any of the symptoms discussed in this article a good place to start is to take our free sleep assessment – this may help frame your conversation with your doctor. Good luck!