obstructive sleep apnea can cause cognitive decline, study says
researchers suggest that the causes of symptoms like memory loss and mood changes in people with osa include low oxygen and high carbon dioxide in the blood.
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people with with severe obstructive sleep apnea had poor executive functioning, short-term memory and social and emotion recognition. getty
a new study has found that obstructive sleep apnea can have a devastating effect on the cognitive abilities of otherwise healthy people. although previous research has suggested a link between the two, the current study, published in the journal frontiers of sleep, found that osa can cause cognitive decline, even in the absence of the comorbidities thought to contribute to the disorder. around 5.4 million canadians have either been diagnosed with sleep apnea or are considered to be at high risk.
osa occurs when the upper airways become blocked, often because the soft tissue at the back of the throat collapses and obstructs the flow of oxygen to the lungs. many of the symptoms of the disorder are felt the next day, including a morning headache, fatigue, irritability or mood changes, poor concentration, memory loss or a lowered sex drive. people who are overweight or have obesity, drink or smoke heavily or who have diabetes face the greatest risk of diagnosis.
“we show poorer executive functioning and visuospatial memory and deficits in vigilance, sustained attention and psychomotor and impulse control in men with osa,” said ivana rosenzweig, lead author of the study and a neuropsychiatrist who heads the sleep and brain plasticity centre at king’s college london. “most of these deficits had previously been ascribed to comorbidities.
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“we also demonstrated for the first time that osa can cause significant deficits in social cognition.”
to arrive at their results, the group recruited a relatively rare group of 27 men, aged 35 to 70, who were recently diagnosed with mild to severe osa and had no comorbidities. these patients can be hard to find because most people with osa also suffer from cardiovascular or metabolic disease, diabetes, stroke, chronic inflammation or depression. the group did not smoke or abuse alcohol and were not considered to be obese by their body mass index.
researchers also assembled a control group that consisted of seven men without osa, matched to the other group by age, bmi and education. they used a number of measures, including the watchpat test, to confirm the presence or absence of osa before assessing the cognitive function of the two groups.
obstructive sleep apnea was found to affect short-term memory
they found that subjects with severe osa exhibited poorer vigilance, executive functioning, short-term visual recognition memory and social and emotion recognition than the control group. patients with mild cases of the disorder fared better on these measures but still worse than those without osa.
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“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,” they wrote.
the team concluded that obstructive sleep apnea is capable of causing these deficits by itself even though previous research has typically directed the blame at the comorbidities.
while the precise manner by which osa causes cognitive decline remains unclear, the team suggested these deficits could be the result of intermittent low oxygen and high carbon dioxide in the blood of patients. changes in blood flow to the brain, sleep fragmentation and neuroinflammation may also be contributing factors.
“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.
it’s also unclear whether or not the presence of comorbidities contributes to the cognitive deficits or simply occurs alongside them.
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“our study is a proof of concept,” rosenzweig said. “however, our findings suggest that comorbidities likely worsen and perpetuate any cognitive deficits caused directly by osa itself.
“what remains to be clarified in future studies is whether comorbidities have an additive or synergistic effect on the latter deficits and whether there is a difference in brain circuitry in osa patients with or without comorbidities.”
dave yasvinski is a writer with healthing.ca
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