African-Americans ages 65 to 90 who reported trouble falling asleep did worse on tests of short-term and working memory than those who nodded off more quickly, Alyssa A. Gamaldo, a Ph.D. candidate at North Carolina State University, and colleagues reported in the November issue of Research on Aging.
The study suggested that identifying and treating sleep difficulties in older patients could help preserve cognitive functioning, the researchers said.
"If we can better understand how sleep quantity, as well as quality, influences general cognitive functioning, perhaps we could better maintain memory throughout life -- including later in life," Gamaldo said.
There have been several studies on sleep difficulties and cognitive performance in young adults, but few in older patients, "which is surprising given that sleep disturbances are common in the elderly," the researchers said.
So the researchers examined 174 patients ages 65 to 90 (mean age 72; 123 females) from the Baltimore Study of Black Aging.
Cognitive performance was assessed using the Mini-Mental State Examination, Forward Digit Span task, Backward Digit Span task, Alpha Span task, and California Verbal Learning test.
Of the total sample, 51 participants (29.3%) reported trouble falling asleep over the past year.
Trouble sleeping was significantly negatively associated with cognitive performance on the digit span and alpha span tasks (P<0.05) -- tests of short-term and working memory, respectively.
The researchers found a similar trend for the Mini-Mental State Examination and California Verbal Learning test, but the relationship was not significant.
Even after controlling for age, gender, education, self-reported health status, and income, the researchers found that difficulty falling asleep was associated with worse performance on the short-term and working memory tests.
Some of the other variables were also significant predictors of cognitive performance:
- Age was negatively associated with the digit span task (P<0.05), suggesting that with increased age, short-term memory performance decreased.
- Women did significantly better than men on the alpha span task (P<0.05) and on the Mini-Mental State Examination (P<0.01).
- With exception of the California Verbal Learning test, education was positively associated with cognitive measures.
- Self-reported health was positively significantly associated with the alpha span task (P<0.01).
- Income was positively associated with the digit span and alpha span tasks but negatively associated with the California Verbal Learning test.
Previous studies have suggested that the relationship between cognition and sleep complaints is influenced by increased depressive symptoms, the researchers said. But when depression was added to the regression model, they found that trouble falling asleep was still a significant unique predictor of cognitive performance.
"The relationship between cognition performance and sleep complaints does not appear to be exacerbated by depression or old age," the researchers said.
The study suggested that sleep could be a confounding variable in cognition studies on older patients, the researchers said.
They also said that further research on the relationship between sleep difficulties and cognitive performance needs to be done before clinical recommendations can be made.
They said their study was limited because measures of cognitive performance like reasoning processing speed were not included in the analyses, which might reveal a better estimate of "how sleep effects all cognitive domains." They were also limited by self-reported data and focusing only on falling asleep as a measure of sleep disturbance.
|The researchers reported no conflicts of interest.|
- Reviewed by Dori F. Zaleznik, MD Associate Clinical Professor of Medicine, Harvard Medical School, Boston
Research on AgingSource Reference: Gamaldo A, et al "The relationship between reported problems falling asleep and cognition among African-American elderly" Research on Aging 2008; 30: 752-767.