After a bad night's sleep, you are unlikely to be in the best of moods. But according to a new study, your bad mood may be down to lack of quality sleep, rather than lack of quantity.
Published in the journal Sleep, the study found that people whose sleep was frequently interrupted for 3 consecutive nights reported significantly worse mood than those who had less sleep due to later bedtimes.
Lead study author Patrick Finan, an assistant professor of psychiatry and behavioral sciences at Johns Hopkins University School of Medicine in Baltimore, MD, and colleagues say their findings indicate sleep interruption is more detrimental to mood than lack of sleep, which may shed light on the association between depression and insomnia.
According to the National Sleep Foundation, adults aged 18-64 should aim to get around 7-9 hours of sleep each night, while those aged 65 and older should get around 7-8 hours of sleep nightly. The Foundation say getting enough sleep can help boost the immune system, productivity and mood.
But increasingly, studies are showing that the quality of sleep is just as important as duration of sleep. "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," notes Finan.
Interrupted sleep led to 31% reduction in positive mood
Finan and colleagues demonstrated the effect of disrupted sleep on mood in their study of 62 healthy men and women who, over 3 consecutive nights in a clinical research suite, were randomized to one of three sleep conditions.
One group had uninterrupted sleep each night, one group had delayed bedtimes, while the remaining group was deliberately awakened eight times during sleep each night.
The sleep stages of each subject were monitored using polysomnography, which records brain waves, blood oxygen levels, breathing, heart rate and eye and leg movements during sleep.
At the end of each night, participants were asked to report how strongly they felt positive or negative emotions, such as anger or cheerfulness, which the researchers assessed to determine their mood.
While there were no differences in mood between groups after the first night, participants in the interrupted sleep group experienced a 31% reduction in positive mood after the second night, while those in the delayed sleep group experienced a 12% reduction in positive mood. These reductions persisted after the third night.
The team says there were no significant differences in negative mood between the delayed sleep group and interrupted sleep group on any of the 3 days, indicating that interrupted sleep has a more adverse impact on positive mood.
Poor slow-wave sleep may explain link between insomnia, depression
On assessing the polysomnography results over the 3 nights, the researchers found that the interrupted sleep group experienced shorter periods of slow-wave sleep, or deep sleep - the sleep stage that is deemed important for body repair and maintenance - than the delayed sleep group.
- Insomnia is when a person has trouble falling asleep, maintaining sleep or frequently awakens during sleep
- Insomnia is only deemed a disorder when it causes significant distress or anxiety, or when it results in daytime impairment
- It is estimated that around 1% of children and 7% of adolescents in the US have insomnia.
What is more, the team found that this lack of slow-wave sleep among the interrupted sleep group was significantly associated with the reduction in positive mood, and that disturbed sleep impacted certain aspects of positive mood, including friendliness and feelings of sympathy.
The team believes their findings help explain why many people with chronic insomnia - a sleep disorder that affects around 10% of the US population - experience depression; it may be down to insufficient amounts of slow-wave sleep.
"Many individuals with insomnia achieve sleep in fits and starts throughout the night, and they don't have the experience of restorative sleep," explains Finan. "You can imagine the hard time people with chronic sleep disorders have after repeatedly not reaching deep sleep."
He notes, however, that further studies are warranted to gain a better understanding of the sleep stages experienced by people with insomnia.
Last month, Medical News Today reported on a study suggesting that adults may only need 6.5 hours sleep each night.