Sleep duration may influence cognition among older individuals, according to a presentation of data generated from the Nurses Health Study.
Elizabeth Devore, ScD, of Brigham and Womens Hospital in Boston, and colleagues examined data for more than 15,000 NHS participants. All were age 70 or older at their first cognitive examination between 1995 and 2000. Follow-up cognitive assessments were conducted every other year for six years.
The researchers found that participants who slept five or fewer hours per day had lower average cognition than those who slept seven hours per day. Those who slept nine or more hours per day also had lower cognition than those who slept seven hours per day. Too little or too much sleep was cognitively equivalent to aging by two years.
When the researchers evaluated the effects of change in sleep duration from mid- to later-life, they observed that women whose sleep changed by two hours per day or more had worse cognitive function than those with no change in sleep duration, independent of their initial sleep duration.
To explore sleep duration in relation to an early biomarker of Alzheimers, the scientists examined the association with plasma levels of a ratio of proteins indicative of Alzheimers disease brain changes beta amyloid 42/40 ratio, which was measured in a small subset of women who provided blood samples in 1999-2000. They found that sleep durations of more than seven or less than seven hours per day were associated with declining ratios of beta amyloid 42/40 compared to sleep durations of seven hours per day.
“Our findings support the notion that extreme sleep durations and changes in sleep duration over time may contribute to cognitive decline and early Alzheimers changes in older adults,” Devore said in a news release. “The public health implications of these findings could be substantial, as they might lead to the eventual identification of sleep- and circadian-based strategies for reducing risk of cognitive impairment and Alzheimers.”
The study was presented July 16 in Vancouver at the Alzheimers Association International Conference.