The Pittsburgh Sleep Quality Index (PSQI) (19 (link)) was used to assess sleep quality over the previous month (with scores >5 indicating poor sleep quality). Participants were asked to report usual bedtime, wake-up time, sleep-onset latency, and actual sleep duration on weekdays and weekends over the previous month. Participants were also asked whether they had a diagnosis of obstructive sleep apnea (OSA), and those without a previous diagnosis completed the Berlin questionnaire to assess the risk of OSA, which categorizes respondents as high or low risk of having OSA (18 (link)). Participants who had a diagnosis of or were at high risk for OSA were identified together as a group with presence or high risk of OSA (OSA/risk).
The following circadian and sleep parameters were calculated. Mid-sleep time was calculated as the midpoint between sleep onset (bedtime plus sleep latency) and wake time. The primary outcome measure of mid-sleep time on free days (MSF), a metric of chronotype, was derived from mid-sleep time on weekend nights with further correction for calculated sleep debt as previously described (20 (link),21 (link)). Specifically, the MSF equals the mid-sleep time on weekend nights subtracting 0.5 times the sleep debt, which is calculated as the difference between sleep duration (duration from sleep onset time until wake time) on weekends minus the weekly average sleep duration. This metric was first proposed by Roenneberg and colleagues with the assumption being that sleep timing on days when unconstrained by the social clock would more accurately reflect the underlying phase of the circadian system (22 (link)). Social jetlag, a behavioral indicator of circadian misalignment, was calculated based on the absolute difference between mid-sleep time on weekdays and weekends (9 (link)).
Sleep duration was computed using a weighted average of self-reported actual sleep duration between weekdays and weekends [(reported weekday actual sleep duration × 5 + reported weekend actual sleep duration × 2)/7]. In addition, because the perception of not getting enough sleep on weekdays has been shown to be better correlated with HbA1c than the reported sleep duration itself (15 (link)), perceived sleep debt was calculated using the difference between participants’ preferred weekday sleep duration (i.e., how many hours they would choose to sleep if their job, family, or other responsibilities did not limit the number of hours they slept) and their self-reported actual weekday sleep duration. Perceived sleep debt is a subjective variable that is likely to combine insufficient sleep duration and poor sleep quality.
The following circadian and sleep parameters were calculated. Mid-sleep time was calculated as the midpoint between sleep onset (bedtime plus sleep latency) and wake time. The primary outcome measure of mid-sleep time on free days (MSF), a metric of chronotype, was derived from mid-sleep time on weekend nights with further correction for calculated sleep debt as previously described (20 (link),21 (link)). Specifically, the MSF equals the mid-sleep time on weekend nights subtracting 0.5 times the sleep debt, which is calculated as the difference between sleep duration (duration from sleep onset time until wake time) on weekends minus the weekly average sleep duration. This metric was first proposed by Roenneberg and colleagues with the assumption being that sleep timing on days when unconstrained by the social clock would more accurately reflect the underlying phase of the circadian system (22 (link)). Social jetlag, a behavioral indicator of circadian misalignment, was calculated based on the absolute difference between mid-sleep time on weekdays and weekends (9 (link)).
Sleep duration was computed using a weighted average of self-reported actual sleep duration between weekdays and weekends [(reported weekday actual sleep duration × 5 + reported weekend actual sleep duration × 2)/7]. In addition, because the perception of not getting enough sleep on weekdays has been shown to be better correlated with HbA1c than the reported sleep duration itself (15 (link)), perceived sleep debt was calculated using the difference between participants’ preferred weekday sleep duration (i.e., how many hours they would choose to sleep if their job, family, or other responsibilities did not limit the number of hours they slept) and their self-reported actual weekday sleep duration. Perceived sleep debt is a subjective variable that is likely to combine insufficient sleep duration and poor sleep quality.
