Sleep apnoea possibly linked to cancer risk in women

"Snoring or waking up exhausted 'could be linked to cancer'," reports the Sun.

Obstructive sleep apnoea (OSA) is a relatively common condition where the walls of the throat relax and narrow during sleep, interrupting normal breathing.

This makes people wake up briefly to catch their breath, though many people with OSA do not remember doing so.

This can lead to interrupted and poor-quality sleep, meaning people wake up tired.

People with OSA may also snore, although not everyone with sleep apnoea snores.

Researchers studied almost 20,000 adults referred to sleep clinics in a European network.

They found 2% of people who'd been assessed for OSA from 2007 to 2016 had cancer.

They then compared sleep test results for people with and without cancer.

They said people with OSA were more likely to have cancer, but when they took account of other potential risk factors, they found the results only remained true for women.

The study does not prove that OSA causes cancer. Cancer rates in the group were quite low.

Also, there could be an underlying factor (or factors) that increases the risk of both cancer and OSA, such as diet and lack of exercise.

If you're concerned you may have OSA, see a GP as treatments are available.

Aside from the adverse effect on quality of life, untreated OSA can put people at risk of accidents caused by lack of sleep.

Read more about treating obstructive sleep apnoea

Where did the story come from?

The researchers came from Aristotle University of Thessaloniki, Democritus University of Thrace and the University of Crete in Greece, the University of Palermo in Italy, University College Dublin in Ireland, Royal Infirmary Edinburgh in Scotland, Grenoble University Hospital in France, Ege University in Turkey, the Institute of Tuberculosis and Lung Diseases in Poland, St Ann's University Hospital in the Czech Republic, the University of Turku in Finland, and Sahlgrenska University Hospital in Sweden.

The study was funded by European Union COST action B26 and the European Respiratory Society.

It was published as a research letter in the peer-reviewed European Respiratory Journal.

The Sun and the Mail Online reporting was appropriate, as both were fairly cautious in their handling of the study's implications.

They did not claim that OSA causes cancer, and included comments from other researchers pointing out the low overall rates of cancer in the study.

What kind of research was this?

This was a cross-sectional study.

This type of study is useful for looking for links between factors, such as OSA and cancer, but cannot show whether one causes another.

Other factors common to both conditions might be involved.

What did the research involve?

Researchers reviewed the records of patients aged 18 or over who were assessed for OSA in a participating sleep laboratory between 2007 and 2016.

People were diagnosed after taking either polysomnography or polygraphy sleep tests.

These tests monitor brain waves, muscle tone and movements, airflow through the mouth and nose, heart rate and blood oxygen levels, and were performed while the person was asleep.

Researchers checked how many people referred for OSA testing had cancer. They then compared sleep test results for people with and without cancer.

Test results included overall severity of sleep apnoea, time with low oxygen blood saturation (less than 90%), and mean and lowest oxygen blood saturation.

They adjusted their figures to take account of a number of potential confounding factors:

• age
• gender
• body mass index (BMI)
• smoking
• alcohol use

What were the basic results?

Of the 19,556 patients, 388 (2%) had cancer.

Men and women

When looking at results for women and men together, only a single measure (time with low oxygen blood saturation) was linked to a higher chance of having cancer.

And this was only by a 10% increase in relative risk, which is quite small when considering the overall risk was only 2% (odds ratio [OR] 1.1, 95% confidence interval [CI] 1 to 1.2)

Women only

When the researchers looked at the results separately for women, they found women with OSA were 79% more likely to have cancer than women whose results showed they did not have OSA (OR 1.79, 95% CI 1.09 to 2.95).

Women with severe OSA were twice as likely to have cancer than those without OSA (OR 2.15, 95% CI 1.19 to 3.87).

Low blood oxygen saturation was also linked to a 3% higher chance of having cancer for women (OR 1.03, 95% CI 1.01 to 1.06).

The most common cancers were breast, prostate, gynaecological, lymphoma and thyroid cancers.

How did the researchers interpret the results?

The researchers said: "The design of our study does not allow speculation about a causal relationship between cancer prevalence and OSA.

"However, the observed interaction between them suggests a possible OSA related mechanism in carcinogenesis [development of cancer] with higher susceptibility [risk] in females."

Conclusion

If you always wake up tired, snore heavily or are concerned that you may have OSA, it's best to check it out with a GP.

The GP can look for other possible causes for your symptoms, and if necessary refer you for assessment at a sleep clinic.

Although headlines about cancer and snoring are worrying, there's no need to be concerned as a result of this study.

The study does not show that OSA causes cancer. It only shows there may be a link between the 2 conditions.

The low number of people who had cancer in the study shows it's unlikely that sleep apnoea has a big effect on cancer.

There are many reasons why people with OSA might be more likely to have cancer, including common risk factors like obesity, smoking and increased age.

While the researchers tried to take account of these in their study, they could not control for other factors, such as diet, physical exercise and genetics.

There are other weaknesses in the study. Some of the results varied by the type of testing used. This makes the overall results less reliable.

Lifestyles measures, such as losing weight (if you're overweight), drinking less alcohol and not smoking, may help reduce the symptoms of OSA.

Find out more about OSA, including symptoms and treatment