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.

The most common form of sleep apnoea is obstructive sleep apnoea (OSA)⁷. The word obstructive is key, as this type of sleep disorder occurs when the upper airways (in your nose and throat) get obstructed, or blocked, while you sleep, often creating a loud snoring sound. When this happens your breathing may stop for periods of 10 seconds or longer, which are called apnoeas. These apnoeas cause you to wake up briefly to gasp for air, before going back to sleep. This can happen hundreds of times a night, although you might not realise it… What you probably will notice are symptoms such as feeling tired in the morning, and having excessive daytime sleepiness even after a full night in bed.

Other common symptoms of OSA include:

• Memory problems
• Morning headaches
• Feeling depressed or low in mood⁸
• Night sweats⁹
• Decreased libido¹⁰
• Needing to wee frequently at night¹¹
• and finally… weight gain¹²

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.

While we’ve seen that obesity is a risk factor for OSA, it’s certainly not the only one – which may help explain why people who are not overweight can also have the condition. Other risk factors include:

• Being male¹⁶
• Having a family history of sleep apnoea¹⁷
• Advancing age (particularly over 55 years)¹⁸
• Taking certain sedatives¹⁹
• Drinking alcohol²⁰ (particularly before bed)
• Smoking²¹

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…

If a person has OSA and doesn’t get diagnosed or treated, then the symptoms discussed above will continue to negatively impact their quality of life. But reducing symptoms is not the only benefit of treating sleep apnoea (although it’s a pretty welcome one!).

It’s also been shown that people with untreated OSA have a higher risk of health conditions such as:

• Hypertension (high blood pressure)³¹
• Cardiovascular disease, such as coronary heart disease or stroke^32-34
• Type II diabetes³⁵

These also happen to be conditions that people living with obesity are more likely to experience, showing again how obesity and sleep apnoea are interrelated…

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.

Since OSA and obesity seem so closely linked, you might think the easiest solution to sleep apnoea is to lose weight. But it’s not quite as simple as that…

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.

Treating your OSA with CPAP therapy has benefits that are related to the reduction in sleep apnoea symptoms, such as a more positive mood³⁸, more energy during the day³⁹ (so you’re more likely to feel like exercising and keeping fit!), a clear mind³⁸ and even a lower risk of road accidents^40,41.

On top of this there are also benefits for your health – and in particular your cardiovascular health:

• 64% reduction in risk of cardiovascular disease⁴² (compared to those who are not treated for OSA)
• Lower blood pressure during the day and night⁴³

Perhaps most striking of all, a recent analysis revealed that all-cause mortality (the total number of deaths in a group, regardless of what caused the deaths) was reduced in OSA patients who stuck to their therapy⁴⁴.

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.