A small new study shows that obstructive sleep apnea (OSA), which leads to headaches, disrupted sleep, loud snoring, and other health issues, may come with another complication: cognitive decline at an earlier age.

In people with OSA, the throat muscles relax and prevent the lungs from getting air, resulting in the sleeper not breathing for a moment. It's the most common sleep-related breathing disorder. While it can be treated with certain devices and surgery, it's considered a serious medical condition that comes with an increased risk of health complications such as heart disease.

OSA has long been linked with cognitive problems, psychiatric issues including depression, and neurodegenerative diseases such as Alzheimer's. However, what hasn't been clear is whether these are caused by OSA or by some of the medical issues related to OSA.

"We show poorer executive functioning and visuospatial memory and deficits in vigilance, sustained attention, and psychomotor and impulse control in men with OSA," says neuropsychiatrist Ivana Rosenzweig from King's College London in the UK.

"Most of these deficits had previously been ascribed to comorbidities. We also demonstrated for the first time that OSA can cause significant deficits in social cognition."

The latest study involved 27 men aged between 35 and 70, with a new diagnosis of mild to severe OSA and no comorbidities – that is, other health issues or diseases that may or may not be linked to OSA. Another 7 men matched for age, BMI, and education but not OSA were used as a control group.

In cognitive tests, the men with OSA scored lower for sustained attention, executive functioning, short-term visual recognition memory, and social and emotion recognition than the control group. The more severe the OSA, the worse the scores compared to the control group.

That these study participants had no other health issues – which is "rare" in people with OSA, according to researchers – suggests that the cognitive decline observed in the tests is due to OSA and not something else. Previously, this mental deterioration had been attributed to other conditions, such as systemic hypertension or type 2 diabetes.

"Our findings suggest that distinct, OSA-driven processes may be sufficient for cognitive changes to occur as early as in middle age, in otherwise healthy individuals," write the researchers in their published paper.

What this research doesn't address in detail is what the root cause of this link might be, but the team has some ideas: the way OSA interferes with the oxygen and carbon dioxide levels in the blood might be one explanation.

OSA is also linked to changes in the blood flow to the brain, inflammation in the brain, and, of course, fragmented sleep. Issues with quality and quantity of sleep have long been associated with a higher risk of developing cognitive problems.

With as many as a billion people potentially having OSA – most of whom might not even be aware of it – it's important to get answers to these questions. The condition is thought to affect as many as 34 percent of men and 17 percent of women.

As well as studying larger and more diverse groups with OSA, the researchers are keen to look more closely at how it affects the brain's circuitry and how related comorbidities might impact the onset of cognitive decline.

"This complex interplay is still poorly understood, but it's likely that these lead to widespread neuroanatomical and structural changes in the brain and associated functional cognitive and emotional deficits," says Rosenzweig.

The research has been published in Frontiers in Sleep.