For a long time, obstructive sleep apnea (OSA) was considered to be a disease that mostly affected men. Today, women are being diagnosed more often. But still, 3-to-5 times more men are diagnosed than women. MyApnea founder, Dr. Susan Redline, and a team of researchers from Brigham and Women’s Hospital and Yale School of Medicine set out to understand how sleep apnea presents in men and women and its impact on diagnosis and health impact.

For a long time, Dr. Redline had a hunch that sleep apnea might present differently in men and women. This could mean that men and women may need to be diagnosed and treated differently for sleep apnea. Dr. Redline explained the motivation for this new study: “Here, we begin to drill down to understand how sleep apnea may differ and how common approaches to scoring sleep studies may underestimate sleep apnea in women.”

The study looked at the sleep studies of 2,057 people who participated in a study called the ‘Multi-Ethnic Study of Atherosclerosis’ (MESA). While the study participants slept, advanced in-home sleep equipment recorded their breathing, brain activity, body movements, and more. These signals allowed the team to measure not only how severe the sleep apnea was for each person but also how individual breathing pauses (apneas) differed in their duration, impact on oxygen levels, and likelihood to occur in REM (dream) or other stages of sleep.

They looked at the score most commonly used to diagnose sleep apnea: apnea-hypopnea index (AHI). The AHI summarizes the number of times someone’s breathing pauses per hour while they sleep. If you stop breathing more than 15 times every hour, your AHI is greater than 15 and you would be diagnosed with ‘moderate to severe sleep apnea’.

That’s how things normally work. But, in this study, the team challenged the traditional way of doing things and calculated AHI in alternative ways. For example, they looked at the number of times people stopped during REM and non-REM sleep. When they calculated the AHI this way, the team found that during non-REM sleep, twice as many men as women had an AHI score greater than 15. But during REM sleep, the men and women had equal scores.

This may be an especially important discovery because there is growing evidence that sleep apnea during REM sleep is associated with cardiovascular risks. Even though some women may not have the classic AHI score of 15, treatment may be important to protect heart health if they are having many AHIs during REM sleep.

Another important way that sleep apnea can be defined is oxygen desaturation. When people stop breathing during an apnea, their oxygen levels drop. Medicare only provides coverage to treat people within a strict level of oxygen desaturation. Redline and colleagues compared this Medicare definition to less strict levels that are not measured in most at-home sleep studies. The number of women with an elevated AHI almost doubled.

“This suggests that women may be under-diagnosed when we use the Medicare definition of sleep apnea,” said Redline. “Women who have been evaluated using only home-based sleep studies should continue to speak to their doctor if they have not been diagnosed with sleep apnea but continue having symptoms.”

The study also showed that the underlying mechanisms for sleep apnea differ in men and women. The apneas occurring in men were associated with measures indicating greater collapsibility of the throat while apneas occurring in women more likely stimulated abrupt changes in breathing.

For a long time, OSA has had the reputation of being a man’s disease. This new study shows that OSA may be a women’s disease too- we just haven’t applied sex-appropriate methods for diagnosing it. Going forward, we also need to consider how to use this knowledge to develop new treatments that work in both men and women.

The complete published article in the journal SLEEP can be found here.

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