Researchers at Penn State University College of Medicine placed 30 study participants on a sleep schedule designed to mimic a sleep-restricted workweek followed by a weekend with extra recovery sleep.
At several points along this schedule, the researchers evaluated the participants’ health and performance through a variety of tests.
The healthy adults who were normal sleepers were put on a 13-day schedule that involved spending nights in a sleep lab. For the first four nights, the participants were allowed to sleep for 8 hours, setting a baseline for a healthy, normal amount of sleep.
For the next six nights, however, the researchers woke the subjects up two hours earlier. Then for the following three nights, the participants were allowed to sleep for 10 hours.
The researchers monitored the subjects’ brain waves while they slept. At three different times during the 13-day schedule, the participants spent whole days at the lab taking part in various tests: after the four days of baseline sleep, after five days of restricted sleep, and after two days of recovery sleep.
During sleep restriction, levels of a hormone that’s a marker of stress didn’t change, but were significantly lower after recovery.
However, the participants’ scores on a performance test that assessed their ability to pay attention dropped significantly after sleep restriction and did not improve after recovery.
This last result suggests that recovery sleep over just a single weekend may not reverse all the effects of sleep loss during the workweek.
During the testing, the subjects gave blood samples every hour, which were tested for levels of interleukin-6 (a marker of inflammation) and cortisol (a hormone secreted during stress).
The researchers also tested how quickly the participants fell asleep when allowed to nap several times during those days. The participants also filled out questionnaires to assess how sleepy they felt.
To evaluate their performance, the subjects participated in a test in which they were asked to press a button whenever a dot appeared on a screen, which measured how well they were able to pay attention.
The researchers found that after five days of restricted sleep, the participants were much sleepier than they were at the beginning of the study. Their interleukin-6 levels also increased sharply during restricted sleep, though their cortisol levels remained the same. Their performance on the attention test also got worse.
After two days of recovery sleep, tests showed that the participants were less sleepy. Their interleukin-6 levels reduced, and their cortisol levels decreased significantly compared to baseline, possibly suggesting that the volunteers were sleep-deprived before the study started.
Interestingly, however, their performance on the attention test didn’t improve after recovery sleep.
Though many indicators of health and well being improved after recovery sleep, these findings show that extra weekend sleep may not fix all the deficits created by lost sleep during the workweek.
“Two nights of extended recovery sleep may not be sufficient to overcome behavioral alertness deficits resulting from mild sleep restriction,” the authors said. “This may have important implications for people with safety-critical professions, such as health-care workers, as well as transportation system employees (drivers, pilots, etc.).”
The researchers note that even though these results provide some insight into the health effects of a single week of sleep loss and recovery, reliving the cycle over and over again may have more significant health effects that this research doesn’t reveal.
“The long-term effects of a repeated sleep restriction/sleep recovery weekly cycle in humans remains unknown,” the authors said.
Source: American Physiological Society