Interrupted sleep worse for mood than shorter bedtime

Being interrupted while sleeping at night may affect the mood more than not getting enough sleep as it can reduce feelings of sympathy and friendliness, a new study suggests.
Researchers studied 62 healthy men and women randomly subjected to three sleep experimental conditions in an inpatient clinical research suite - three consecutive nights of either forced awakenings, delayed bedtimes or uninterrupted sleep.
Participants subjected to eight forced awakenings and those with delayed bedtimes showed similar low positive mood and high negative mood after the first night, as measured by a standard mood assessment questionnaire administered before bedtimes.
Participants were asked to rate how strongly they felt a variety of positive and negative emotions, such as cheerfulness or anger.

Researchers said that significant differences emerged after the second night. The forced awakening group had a reduction of 31 per cent in positive mood, while the delayed bedtime group had a decline of 12 per cent compared to the first day.
Researchers add they did not find significant differences in negative mood between the two groups on any of the three days, which suggests that sleep fragmentation is especially detrimental to positive mood.

"When your sleep is disrupted throughout the night, you don't have the opportunity to progress through the sleep stages to get the amount of slow-wave sleep that is key to the feeling of restoration," said lead author Patrick Finan, an assistant professor at the Johns Hopkins University School of Medicine in US.

Although the study was conducted on healthy subjects with generally normal sleep experiences, Finan said that the results are likely to apply to those who suffer from insomnia.
"Many individuals with insomnia achieve sleep in fits and starts throughout the night, and they don't have the experience of restorative sleep," Finan said.
To study the link between depressed mood and insomnia, researchers used a test called polysomnography to monitor certain brain and body functions while subjects were sleeping to assess sleep stages.
Compared with the delayed bedtime group, the forced awakening group had shorter periods of deep, slow-wave sleep.
The lack of sufficient slow-wave sleep had a statistically significant association with the subjects' reduction in positive mood, the researchers said.

They also found that interrupted sleep affected different domains of positive mood; it reduced not only energy levels, but also feelings of sympathy and friendliness.
Finan said that the study also suggests that the effects of interrupted sleep on positive mood can be cumulative, since the group differences emerged after the second night and continued the day after the third night of the study.
The study was published in the journal Sleep.