Older women with sleep disordered breathing may face greater risk of dementia

Older women who have sleep-related breathing problems may be at greater risk of problems with mental function, including dementia, according to a new study in the August 10, 2011 issue of the Journal of the American Medical Association.

"Humans spend almost one third of their lives sleeping, so anything that disturbs or interrupts that on a regular basis can have a big impact on our health," says Katie Stone, PhD, senior scientist at the California Pacific Medical Center Research Institute - part of the Sutter Health network - and co-author and principal investigator on the study. "Sleep disordered breathing, which is commonly known as sleep apnea, is caused by the collapsing or constricting of the throat during sleep. This causes the individual to stop breathing for a brief period of time - anywhere from a few seconds to a minute - and therefore the blood oxygen levels drop. These periodic dips in oxygen levels may have serious long-term consequences."

The researchers followed nearly 300 women with a mean age of 82. None of the women had no signs or symptoms of impaired mental function at the start of the study. More than 100 of these women were diagnosed with some form of sleep disordered breathing (SDB) which is defined as having 15 or more apneas with intermittent interruptions of breathing per hour of sleep. Five years later the researchers followed up with tests of memory, attention and concentration, to measure whether the women's cognitive status could be described as normal, dementia or mild cognitive impairment (MCI). The researchers found that the women with SDB were nearly twice as likely to develop mild cognitive impairment or dementia compared to those who did not suffer from SDB.

"We've known for some time that there is a link between SDB and brain function, but ours is the first study to demonstrate that SDB in cognitively normal older adults is a risk factor for the development of poor cognition over time," says Kristine Yaffe, MD, a researcher with the University of California, San Francisco, and the lead author of the study. "While we cannot conclude from these results that SDB causes cognitive impairment, our study suggests that it may be at least a contributing factor. If SDB is a cause of cognitive impairment then this has enormous public health implications, particularly in light of our aging population. More studies are needed in which older adults with SDB are treated to determine if the decline in mental function can be slowed or prevented."

The so-called "oldest old", namely those 85 and older, is one of the fastest growing segments in the U.S. and is expected to increase by 40 percent during the next decade alone. Previous studies have suggested that the incidence of dementia almost doubles with every 5 years of age and that the prevalence of dementia rises from around 2 - 3 percent in those under 75 years to 35 percent in those 85 years and older.

Dr. Stone says that while this study only involved women it's likely that men may be similarly affected by SDB.

"Our study shows we need to look more closely at the link between SDB and mental function. If we can find better ways to treat, or prevent, SDB we may be able to prevent the development or at least slow down the development of cognitive impairment in older Americans."