July 16, 2007 -- Sleep problems and declining mental skills may go hand in hand, according to a study published in tomorrow's edition of Neurology.
"This study does not mean that an individual with cognitive problems will necessarily develop sleep trouble, but that these elders are at a higher risk of sleep disorders," researcher Kristine Yaffe, MD, states in an American Academy of Neurology news release.
Yaffe works in the psychiatry department of the University of California at San Francisco.
Sleep Problems Studied
Yaffe's team studied more than 2,400 American women for 15 years.
When the study started, the women were at least 65 years old (average age: nearly 69) and didn't have dementia. They took tests of mental skills including memory, language, and attention.
The women repeated the test at the end of the 15-year study. The tests showed declining test scores for 11% to 15% of the women.
At the end of the study, the women also wore a sleep-monitoring device called an actigraph for three nights. The actigraph, which is about the size of a wristwatch, tracks movement and shows when people are asleep or awake.
Sleep Problems and Mental Decline
These women were more likely than women with unchanged test scores to have sleep problems, even when the researchers considered other factors that might affect the results.
Compared with women whose mental skills test scores didn't change, those with declining test scores were about 70% more likely to have poor sleep, almost 60% more likely to take an hour or more to fall asleep, 43% more likely to wake up for at least 90 minutes during the night, and almost 75% more likely to nap for more than two hours daily.
The women didn't wear the actigraphs at the study's start. So the researchers don't know which came first -- poor sleep or mental decline.
The study doesn't show exactly how mental decline and sleep problems are connected. Perhaps those two conditions have a common cause, note Yaffe and colleagues.