The findings, reported in the Journal of the American Geriatrics Society, suggest that so-called sleep-disordered breathing, including sleep apnoea, may be a risk factor for age-related cognitive decline.

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They also open the possibility that treating these sleep-related breathing disorders could prevent mental impairment in some older adults, researchers say.

Sleep-disordered breathing, or SDB, refers to a group of sleep-related breathing problems. Obstructive sleep apnoea, where breathing stops briefly and restarts repeatedly through the night, is one of the most common forms. People with SDB may also have repeated episodes of hypopnoea, during which breathing diminishes but does not stop entirely.

Signs of SDB include chronic snoring and daytime sleepiness owing to poor sleep quality.

Various health risks
Sleep apnoea has been linked to a number of health consequences, including high blood pressure and an increased risk of cardiovascular disease. Whether it affects cognitive function as people age has been less clear.

The new study included 448 women with an average age of 83 who underwent an overnight sleep study to detect breathing problems. They also took standard tests of memory, attention and other cognitive abilities.

In general, the study found, women with SDB were more likely than those without breathing problems to show cognitive impairment. Those with severe breathing problems had a more than three-fold increased risk of impairment.

What's more, the link between SDB and cognitive impairment was particularly strong among women who carried a gene linked to Alzheimer's disease - a variant of the apolipoprotein E gene known as APOE e-4.

Oxygen deprivation damage brain cells
The findings do not prove that night time breathing problems directly contribute to cognitive decline, according to Dr Adam P. Spira, a research fellow at the University of California San Francisco and the lead investigator on the study.

However, he told Reuters Health, it is "quite plausible" that this is the case. In theory, the chronic oxygen deprivation caused by SDB could damage brain cells. Furthermore, women who are genetically vulnerable to dementia may be more susceptible to this damage.

Studies that follow older adults over time, looking at whether SDB predicts future cognitive decline, are now needed, according to Spira. "Future research that provides this evidence would, in turn, suggest that treatment of apnoea could help prevent or reduce cognitive decline," he said.

Regardless of whether this turns out to be the case, though, older adults stand to benefit from having sleep apnoea treated, Spira noted. If treatment eases daytime sleepiness, for example, that could improve older adults' ability to function and boost their quality of life, he said. - (Reuters Health/Amy Norton)

SOURCE: Journal of the American Geriatrics Society, January 2008.

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