A new study published Monday in the Journal of Clinical Sleep Medicine highlights the complex reality of treating sleep apnea, one of the most common sleep disorders, in thinner people.

Researchers examined data from more than 150 patients with obstructive sleep apnea (OSA) who had visited the Prince of Wales Hospital in Australia. Though the condition is most associated with obesity, they found that 52 percent of their patients had a body mass index under 30, half of which were further considered normal weight. And unlike their heavier counterparts, thinner people with sleep apnea were less able to tolerate the most common first-line treatment for the condition, a continuous positive airway pressure (CPAP) device. In addition, 36 percent of non-obese patients reported that they stopped using the device during a follow-up exam compared to 13 percent of obese patients.

"Non-obese OSA patients are a challenging group to treat with existing therapies as they are less adherent and compliant with CPAP therapy compared to obese patients with sleep apnea," said study author Dr. Danny Eckert, an associate professor at the University of New South Wales as well as a researcher at Neuroscience Research Australia, in a statement.

People with obstructive sleep apnea have problems breathing properly during sleep. As they attempt to slumber, their airways regularly collapse, slowing the flow of air in and out of the lungs. Usually, this slowdown leads to loud and chronic snoring, as air barely squeaks past the partially obstructed airway. At worst, the airway becomes completely blocked off, suffocating the sufferer until their bodies reflexively gasp for air.

People with OSA are rarely completely startled awake by this reflex, but the constant cycle of oxygen deprivation and disrupted sleeping wreaks havoc with their overall health. Chronic OSA is thought to contribute to any number of other chronic conditions such as cardiovascular disease, depression, and diabetes.

CPAP therapy helps OSA sufferers by hooking them up to a device that continuously pumps air through their nose and mouth as they sleep, ensuring the airways never fully close. While obese patients often respond well to the treatment, the researchers found that non-obese people are generally lighter sleepers, making the device less effective for them. Doctors may need to approach these OSA cases differently then, noted Eckert.

"Specifically, they may need therapies that target causes other than upper airway anatomy such as sleep promotion aids to allow for deeper more stable sleep and breathing," he explained. "Or they could use these approaches in combination with the CPAP for greater therapeutic advantage.”

While obesity is known to make people vulnerable to OSA due to anatomical changes in the airway, Eckert added that his team’s findings indicate that “doctors and clinicians need to look for other symptoms associated with OSA when patients present with sleeping issues beyond obesity and anatomical issues."

It’s estimated that one of every five Americans suffers from at least mild sleep apnea, with OSA being the most common form.

Source: Gray E, MacKenzie D, Eckert D. Obstructive Sleep Apnea Without Obesity is Common and Difficult to Treat: Evidence for a Distinct Pathophysiological Phenotype. Journal of Clinical Sleep Medicine. 2016.