Older women with a common sleep disorder could be at higher risk of developing dementia, warn researchers.
They found women who have breathing problems during sleep – which reduces oxygen levels in the brain – were up to 50 per cent more likely to develop cognitive impairment or dementia than women who sleep normally.
The research involved only older women, but the mechanism is likely to be important in triggering similar problems in men.
U.S. researchers warn that conditions such as sleep apnoea, where people experience frequent interruptions to breathing during sleep, are widespread.
They affect up to 60 per cent of older people, which means any link could have a ‘large public health impact’, especially as there are treatments for sleep apnoea.
Dr Kristine Yaffe and a team from the University of California, San Francisco, carried out a study involving almost 300 women with an average age of 82 years who did not have dementia.
The women were given medical tests for breathing disorders during sleep, which measured the number of times their breathing was interrupted or briefly ceased while they were asleep, and levels of oxygen deprivation, or hypoxia, in the brain.
One-third met the criteria for sleep-disordered breathing.
After more than four years of follow-up, 36 per cent of the women developed mild cognitive impairment or dementia.
Forty-seven women (45 per cent) with prevalent sleep-disordered breathing developed mild cognitive impairment or dementia compared with 31 per cent of those without sleep-disordered breathing – an increase of 50 per cent in the numbers affected.
Analysis of the data indicated that the presence of sleep-disordered breathing was associated with an increased odds of subsequent mild cognitive impairment or dementia.
The researchers also found that two measures of hypoxia were associated with higher incidence of mild cognitive impairment or dementia.
But the amount of sleep fragmentation or lack of sleep were not associated with risk of cognitive impairment.
A report, in the Journal of the American Medical Association (must credit), says hypoxia appeared to be the main driver behind an increased risk of cognitive impairment.
Dr Yaffe said ‘Given the high prevalence and significant morbidity associated with both sleep-disordered breathing and cognitive impairment in older populations, establishing whether a prospective association exists between sleep-disordered breathing and cognition is important.
‘This is especially important because effective treatments for sleep-disordered breathing exist.
‘Furthermore, the finding that hypoxia and not sleep fragmentation or duration seems to be associated with risk of mild cognitive impairment or dementia provides clues to the mechanisms through which sleep-disordered breathing might promote cognitive impairment.
‘The increased risk for cognitive impairment associated with sleep-disordered breathing opens a new avenue for additional research on the risk for development of mild cognitive impairment or dementia and exploration of preventive strategies that target sleep quality including sleep-disordered breathing.’
The researchers call for bigger studies to investigate the link, which include men.
At least half a million Britons suffer from obstructive sleep apnoea (OSA).
In OSA, the muscles in the airway collapse during sleep, which cut off breathing for at least 10 seconds before brain signals cause contraction of the muscles which re-open the airway.
Not only does it disrupt sleep – for sufferers and those within earshot – and cause exhaustion and daytime sleepiness, the condition appears to increase blood pressure and associated heart problems.
It can be treated using continuous positive airway pressure machines which requires the patient to wear a mask over their nose during sleep.
A bedside blower unit pumps a steady stream of air through the mask, ensuring the throat remains open and the patient gets a full night’s sleep.
Dr Anne Corbett, research manager at the Alzheimer’s Society, said ‘This large study builds on previous work showing that older people who have breathing disorders during sleep have an increased risk of dementia.
‘It also supports the theory that this is due to less oxygen reaching the brain while the person is asleep. It is therefore vital that we identify and treat breathing disorders during sleep to help reduce the risk of dementia in later life.
‘People can cut down their likelihood of developing dementia by up to a third by eating a good diet, keeping a healthy weight and taking regular exercise. It’ s also important to get your blood pressure and cholesterol checked regularly.’