It is still unclear whether comorbidities have similar negative effects on cognition beyond those directly caused by obstructive sleep apnea.
New research suggests that in middle-aged men, obstructive sleep apnea (OSA) could cause early cognitive decline, even in patients who are otherwise healthy and not obese.
OSA is a potentially dangerous condition characterized by relaxed throat muscles during sleep, blocking the airflow into the lungs and repeatedly halting breathing. Common symptoms include restless sleep, loud snoring, daytime sleepiness, and prolonged headaches in the morning, all of which can be highly debilitating for patients and their partners.
Despite these concerns, OSA is currently underdiagnosed. Although it may occur in as much as 15% to 30% of men and between 10% and 15% of women, an estimated 80% of patients do not know they have it. Major risk factors include middle or old age, obesity, smoking, chronic nasal blockage, high blood pressure, and being male.
“We show poorer executive functioning and visuospatial memory and deficits in vigilance, sustained attention, and psychomotor and impulse control in men with OS,” said lead author Ivana Rosenzweig, PhD, MRCPsych, FRCPsych, in the press release. “Most of these deficits had previously been ascribed to co-morbidities. We also demonstrated for the first time that OSA can cause significant deficits in social cognition.”
Investigators studied a group of 27 men between 35 and 70 years of age with a new diagnosis of mild to severe OSA but with no comorbidities. Patients such as these are relatively rare, according to the study, because most men and women with OSA have comorbidities, such as cardiovascular and metabolic disease, stroke, diabetes, chronic systemic inflammation, or depression.
Participants in the study were not currently smokers or alcohol abusers and were not obese. The OSA diagnosis was confirmed by a WatchPAT test of their respiratory function during sleep at home, and by video polysomnography at King’s College sleep center. As a control, the investigators studied a group of 7 age-, body mass index-, and education-matched men without OSA.
In the video-polysomnography tests, the brain waves of sleeping subjects were measured with electroencephalography, while their blood oxygen levels, heart rate, breathing, and eye and leg movements were tracked. The investigators also tested the subjects’ cognitive function with the Cambridge Neuropsychological Test Automated Battery (CANTAB) of tests.
According to the study results, patients with severe OSA had poorer vigilance, executive functioning, short-term visual recognition memory, and social and emotion recognition than the matched controls. Patients with mild OSA performed better in these domains than patients with severe OSA, but worse than the controls.
The most significant deficits were found in the tests assessing both simultaneous visual matching ability and short-term visual recognition memory for non-verbalizable patterns, tests of executive functioning and cued attentional set shifting, in vigilance and psychomotor functioning, and in social cognition and emotion recognition. Based on this, the authors concluded that OSA is sufficient to cause these cognitive deficits, which earlier studies had attributed to the most common comorbidities of OSA, such as systemic hypertension, cardiovascular and metabolic diseases, and type 2 diabetes.
However, the mechanism for this association is still unclear. The investigators speculated that the cognitive deficits are due to intermittent low oxygen and high carbon dioxide in the blood, changes in blood flow to the brain, sleep fragmentation, and neuroinflammation in patients with OSA.
“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,” Rosenzweig said in the press release.
It is also still unclear whether comorbidities have similar negative effects on cognition beyond those directly caused by OSA. Rosenzweig did note that the finding suggests that comorbidities likely worsen and perpetuate any cognitive deficits directly caused by OSA. Future studies should confirm whether comorbidities have an additive or synergistic effect.
Obstructive sleep apnea may directly cause early cognitive decline. News release. EurekAlert. April 6, 2023. Accessed April 6, 2023.