Sleep apneas are a common condition in which the airway collapses or becomes blocked during sleep, causing stalled breathing. Approximately one in five American adults suffers from a sleep apnea, although in many cases these are mild and don’t present much of an issue.

People with sleep apneas can deal with them by sleeping with a CPAP machine, which helps keep the airway open during rest. However, CPAP machines can be inconvenient and uncomfortable. As a result, many patients, even those with more severe sleep apneas, choose not to use these machines, or use them only intermittently.

But not only are people who neglect to use their CPAP machines failing to treat their sleep apneas, they can be creating more medical conditions for themselves in the long term. In a study conducted by Johns Hopkins University, 31 people with moderate to severe sleep apneas took part in a study of the effects of CPAP machine use on overall health. In the study, they spent two nights sleeping in a Johns Hopkins lab. One night, they used a CPAP machine; the other, they didn’t. Over the course of the night, researchers obtained blood samples from all participants.

On the night that the participants did not use the CPAP machine, these blood samples showed low levels of oxygen, and higher levels of fatty acids, sugar, and the stress hormone cortisol. Additionally, the participants slept worse and experienced higher heart rates, higher blood pressure, and stiffer arteries on the night without the CPAP machine.

It’s uncertain whether these results would be as marked–or even, whether they would present themselves at all–with patients with less severe sleep apneas. And the patients in the study also had other health issues, from heart problems to obesity.

Nonetheless, these results suggest that the stress and heart strain caused by untreated sleep apneas can lead to other health issues, including heart disease, risk of stroke or heart attacks, and type 2 diabetes.

Sleep apneas have long been linked with such health issues, but since they are most commonly found in obese patients, it has long been unclear whether the sleep apnea, or the obesity, was the culprit. This study points to sleep apneas playing at least some part in deteriorated hearth health and type 2 obesity risk, and points to the importance of regular CPAP machine use in improving the overall health of those with a sleep apnea.