People overestimate sleep times

Self-reports of total sleep times, both habitually and on the morning after a polysomnogram (PSG), or a sleep test, tend to be higher than objectively measured sleep times, according to a study published in the October 15 issue of the Journal of Clinical Sleep Medicine (JCSM).

Graciela E. Silva, PhD, of Arizona State University, analyzed a total of 2,113 subjects who were 40 years of age or older. The participants were 53 percent female, 75 percent Caucasian and 38 percent obese. Dr. Silva compared the subjects' total sleep time and sleep onset latency obtained from unattended home PSGs to sleep times obtained from the Sleep Heart Health Study (SHHS) Sleep Habits Questionnaire, completed before the PSG and the morning after the PSG. The SHHS Sleep Habits Questionnaire contained questions regarding sleep habits, smoking status as well as cardiovascular and respiratory problems.

The results showed that the mean habitual sleep time was 422 minutes, while the mean morning estimated sleep time was 379 minutes and mean PSG total sleep time was 363 minutes. The mean habitual sleep onset latency was 17 minutes, while the mean morning estimated sleep onset latency was 21.8 minutes and mean PSG sleep onset latency was 16.9 minutes.

Models adjusting for related demographic factors showed that the mean habitual sleep time differed significantly from the PSG total sleep time by 61 minutes. The mean morning estimated sleep time differed fom the PSG total sleep time by 18 minutes.

Further, obese and higher educated people reported less sleep time than their counterparts. Similarly, small but significant differences were seen for sleep latency.

“The findings from this study suggest that results from studies subjectively assessing sleep times may not be comparable to those using objective determinations,” said Dr. Silva.

The SHHS is a prospective multicenter cohort study designed to investigate the relationship between sleep disordered breathing and cardiovascular diseases in the United States.

Those who suspect that they might have a sleep disorder are encouraged to see their primary care physician or a sleep medicine specialist.