Snoring is linked to Alzheimer's disease, new research suggests.
Difficulty breathing while asleep accelerates memory decline in people at-risk of the condition, a study found.
Daytime sleepiness and sleep apnoea is also linked to impaired attention, memory and thinking in people who are genetically susceptible to the degenerative condition, the research adds.
Researchers hope the findings will support sleep-based treatments in people at-risk of developing Alzheimer's.
Study author Dr Susan Redline from Harvard University, said: 'Given the lack of effective treatment for Alzheimer's disease, our results support the potential for sleep-disordered breathing screening and treatment as part of a strategy to reduce dementia risk.'
How the study was carried out
Researchers from Harvard University analyzed 1,752 people with an average age of 68.
The study's participants took part in a sleep study, completed a sleep questionnaire and had their mental function assessed.
So-called sleep-disordered breathing (SDB) was defined as having more than 15 stopped or shallow breaths per hour, as well as loud snoring.
Participants were diagnosed with sleep apnoea if they had more than five stopped or shallow breaths per hour, as well as self-reporting sleepiness.
People were identified as being at-risk of Alzheimer's if they carried a certain variation of a gene known as APOE, which carries cholesterol and supports brain injury repair in healthy people.
Previous studies have demonstrated one-fifth of the population who carry the APOE genetic variation are at an increased risk of Alzheimer's disease.
Key findings
Results revealed that SDB is linked to mental decline when people are genetically at-risk of Alzheimer's.
The findings also show that among such at-risk people, daytime sleepiness is linked with poor attention and memory, as well as slower thinking.
Sleep apnoea is associated with impaired attention and thinking in those at-risk. Apnoea is defined as the muscles and soft tissues in the throat relaxing and collapsing to cause an airway blockage for at least 10 seconds.
The findings were published in the journal Annals of the American Thoracic Society.
What the experts say
Study author Dr Dayna Johnson said: 'Individuals with SDB commonly report problems with cognition and may be at increased risk for dementia.
'Cognitive impairment is highly prevalent among elderly populations, and is associated with increased disability, neuropsychiatric symptoms and healthcare costs.
'Our results suggest that more severe overnight hypoxemia and sleepiness may be related to poorer cognitive function, especially attention, concentration, and process speed in middle-aged to older adults, and that the risk is greater among carriers of APOE, a known risk factor for Alzheimer's disease.
'With use of this type of information, future risk stratification may help to identify individuals at increased risk for SDB-related cognitive deficits'.
Dr Redline added: 'Our study provides further evidence that sleep-disordered breathing negatively affects attention, processing speed and memory, which are robust predictors of cognitive decline.
'Given the lack of effective treatment for Alzheimer's disease, our results support the potential for sleep-disordered breathing screening and treatment as part of a strategy to reduce dementia risk.'
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