Sleep Disorders

16 October 2007

Sleep time badly misjudged

If you think you're getting a good eight hours of sleep each night, the odds are that you're wrong, a study published Monday suggests.

If you think you're getting a good eight hours of sleep each night, the odds are that you're wrong, a study published Monday suggests.

In a study of 2 113 adults age 40 and up, researchers found that people overestimated their usual sleep time by an hour, on average.

When asked how much they typically slept at night, participants reported an average of seven hours. However, it appeared they had been overly optimistic when their sleep times were actually measured with polysomnography.

Polysomnography is a way of objectively gauging sleep time and quality; it uses electrodes to gather data on activity in the brain, muscles, eyes and heart throughout the night. The study is often performed in a sleep lab, but can also be done in the home, using portable equipment.

Sleep overestimated
The new findings, published in the Journal of Clinical Sleep Medicine, suggest that when compared with in-home polysomnography, people often overestimate their sleep time. And this has implications for studies on sleep and health, according to the researchers.

Many studies rely on people's self-reported sleep habits, as polysomnography is expensive and requires "dedicated and experienced personnel," even when done in the home, explained lead study author Dr Graciela E. Silva of Arizona State University in Phoenix.

However, she told Reuters Health, her team's results "indicate that people are not able to estimate their total amount of sleep reliably."

This means that results from studies that rely on self-reports should be viewed with some caution, according to Silva.

A cheaper alternative
An alternative to polysomnography, she noted, is a measure called actigraphy. Actigraphy uses a small, inexpensive device - sometimes worn as a wristwatch - to record a person's movements overnight. "Sleep is inferred when there is relatively little movement," Silva explained.

While polysomnography is more sophisticated and in-depth, actigraphy might offer a more feasible way to measure sleep time in studies, according to Silva.

Beyond the implications for sleep research, the current findings also suggest that many people are not catching all the Zs they think they are.

It's recommended that adults sleep about 8 hours each night, Silva noted, but it appears that many people don't.

SOURCE: Journal of Clinical Sleep Medicine, October 15, 2007. – (Reuters Health)

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Sleep Centre

October 2007


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Dr Alison Bentley is a general practitioner who has consulted in sleep medicine and sleep disorders, in both adults and children of all ages, for almost 30 years. She also researches and publishes on a number of sleep-related topics both in formal research journals and lay publications including as editor of Sleep Matters, an educational newsletter on sleep disorders for doctors.

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