Link between obstructive sleep apnea and early cognitive decline found

New Delhi: Researchers have shown obstructive sleep apnea (OSA) to cause early cognitive decline in middle-aged men, even in patients otherwise healthy and not obese. The international study led by King's College London, UK, studied a group of 27 men between ages 35 and 70, newly diagnosed with mild to severe OSA but without any co-morbidities. The researchers have published their findings in the journal Frontiers in Sleep.

These patients formed a rare cohort for study because men and women with OSA have co-morbidities such as cardiovascular and metabolic disease, stroke, diabetes, chronic systemic inflammation, or depression.

"We show poorer executive functioning and visuospatial memory and deficits in vigilance, sustained attention, and psychomotor and impulse control in men with OSA. Most of these deficits had previously been ascribed to co-morbidities," said Ivana Rosenzweig, lead researcher and a neuropsychiatrist at King's College London.

"We also demonstrated for the first time that OSA can cause significant deficits in social cognition," said Rosenzweig.

CANTAB or 'Cambridge Neuropsychological Test Automated Battery' of tests were used to investigate the cognitive function of subjects.

"The most significant deficits…were demonstrated in the tests that assess 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 lastly, in social cognition and emotion recognition," wrote the authors.

The authors conclude that OSA is sufficient to cause these cognitive deficits, which previous studies had attributed to the most common co-morbidities of OSA such as systemic hypertension, cardiovascular and metabolic diseases, and type 2 diabetes.

The men were currently neither smokers nor alcohol abusers, and were not obese (body mass index or BMI under 30). The researchers studied a group of seven age-, BMI-, and education-matched men without OSA as controls. The scientists also confirmed the OSA diagnosis of patients using WatchPAT test and video-polysomnography.

WatchPAT test is a sleep apnea diagnostic tool that utilizes the peripheral arterial signal (PAT) for diagnosis and measures up to 7 channels (PAT signal, heart rate, oximetry, actigraphy, body position, snoring, and chest motion) via three points of contact.

However, the scientists said that the mechanism through which this happens is unclear yet.

The authors 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 OSA patients.

OSA is a condition whereby during sleep, the throat muscles of people with OSA relax and block the airflow into the lungs, so that they repeatedly stop breathing.

Common symptoms include restless sleep, loud snoring, daytime sleepiness, and prolonged headaches in the morning.

Major risk factors for OSA include middle or old age, being obese, smoking, chronic nasal blockage, high blood pressure, and being male.