Sleep-disordered breathing among older women that leads to deficient oxygenation of the blood (hypoxemia) raises the risk of their developing dementia or cognitive impairment, compared with other older women, researchers from the University of California, San Francisco, reported in JAMA (Journal of the American Medical Association).

As background information, the investigators wrote:

“Sleep-disordered breathing, a disorder characterized by recurrent arousals from sleep and intermittent hypoxemia, is common among older adults and affects up to 60 percent of elderly populations. A number of adverse health outcomes including hypertension, cardiovascular disease, and diabetes have been associated with sleep-disordered breathing.”

Previous studies had shown an association between cognitive impairment and sleep-disordered breathing. However, they were designed in such a way that drawing any compelling conclusions was impossible.

The authors added:

“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.”

Kristine Yaffe, M.D. and team set out to find out whether sleep-disordered breathing rates might be linked to subsequent higher rates of diagnoses of dementia or mild cognitive impairment. Sleep-disordered breathing was measured by monitoring physiological activity during sleep (polysomnography).

The researchers assessed 298 older females who had no signs of dementia when the study began, they had an average age of 82.3 years. Overnight polysomnography was measured between January 2002 and April 2004. This was part of the Study of Osteoporotic Fractures.

A participant with an apnea-hypopnea index of at least 15 events per hour during sleep would be defined as having sleep-disordered breathing. Apnea refers to a complete breathing stop during sleep, while hypopnea refers to partial obstructions of breathing during sleep. The apnea-hypopnea index measures how many apnea and hypopnea events there are per hour during sleep.

They had gathered data on the women’s cognitive status between November 2006 and September 2008. Cognitive status was defined as normal, mild cognitive impairment, or dementia.

They measured hypoxia, sleep fragmentation and sleep duration as underlying mechanisms for any link between sleep-disordered breathing and cognitive impairment.

The authors found that:

  • 35.3% of the 298 elderly females met the criteria for sleep-disordered breathing
  • After a follow-up period of 4.7 years (average)
    – 20.1% developed mild cognitive impairment
    – 15.8% developed dementia
  • 44.8% of those with prevalent sleep-disordered breathing developed dementia or mild cognitive impairment versus 31.1% of the women without the disorder

The researchers say their findings demonstrate that there is a link between sleep-disordered breathing and a higher risk of mild cognitive impairment or dementia later on.

They also found that an oxygen desaturation index of at least 15 and a high proportion of sleeping time in hypopnea or apnea was association with a higher rate of dementia or mild cognitive impairment – even after taking account of several demographic risk factors. The researchers wrote:

“Measures of sleep fragmentation (arousal index and wake after sleep onset) or sleep duration (total sleep time) were not associated with risk of cognitive impairment.”

According to their findings, the authors say the higher risk of cognitive impairment appears to be linked mainly to measures of hypoxia.

They wrote:

“Given the high prevalence of both sleep-disordered breathing and cognitive impairment among older adults, the possibility of an association between the 2 conditions, even a modest one, has the potential for a large public health impact. 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.”

Further studies are required to evaluate the effects and consequences of sleep-disordered breathing, the researchers added. Trials need to be larger than this one, of longer duration, and with more diverse populations.

The investigators added:

“Of interest, our findings suggest a potential role for supplemental oxygen therapy for sleep-disordered breathing in elderly individuals; however, its role requires critical evaluation in intervention studies.”

Nicola Canessa, Ph.D., of the Center for Cognitive Neuroscience, and Luigi Ferini-Strambi, M.D., of the Universita Vita-Salute San Raffaele, Milan, Italy, wrote:

“The study by Yaffe et al and related studies to date suggest that large trials with continuous positive air pressure (CPAP) treatment in elderly participants with sleep-disordered breathing should be performed.

Moreover, in trials evaluating the effects of pharmacological and nonpharmacological (e.g., cognitive training and rehabilitation) interventions on cognitive function in patients with mild cognitive impairment or dementia, the possible coexistence of sleep-disordered breathing should be considered.

Finally, physicians of patients with mild cognitive impairment and sleep-disordered breathing for whom treatment with CPAP may be indicated should consider these results, and future guidelines to formalize the clinical management of patients with mild cognitive impairment should consider the implications of this study and related research.”

Written by Christian Nordqvist