About 44% of people with insomnia also have a mental illness such as depression or generalized anxiety. So it’s no surprise that in healthy female college students there’s a relationship between sleep and mood, or affect.
But just what that relationship is—and how normal variations in sleep and affect might morph into insomnia and/or a mood disorder—hasn’t been established. Here’s what researchers at Kent State University and Henry Ford Hospital have found out.
Insomnia or Mood Disorder: Which Comes First?
Earlier studies have shown that just as depression and anxiety can precede development of insomnia, so sleep problems can precede development of a mood disorder. It’s a two-way street: sometimes depression and anxiety give rise to sleep problems and sometimes insomnia gives rise to depression or generalized anxiety.
But not much is known about how normal, specific emotional states that fluctuate with day-to-day experience affect sleep. Nor is it clear how different aspects of sleep affect people’s mood the next day. Knowing these things might shed light on the vulnerabilities that presage insomnia and mood disorders, making it possible to nip them in the bud. So the Kent State and Henry Ford researchers designed a study to find out more about the relationship between daily affect and sleep.
A Two-Week Study of Female College Students
The study was conducted on 171 healthy young female students at a Midwestern university. The protocol was simple. Every morning for 2 weeks, the women, immediately upon waking up, had to log onto their computers and evaluate feelings they’d had in the past 24 hours and how well they’d slept. To evaluate their affect, they assessed levels of 3 positive and 3 negative emotional states:
- joviality (happy, cheerful, optimistic)
- self-assurance (proud, strong, confident)
- serenity (calm, relaxed)
- fear (afraid, nervous, scared, jittery)
- sadness (sad, alone, lonely, downhearted)
- hostility (angry, hostile, irritable)
They also assessed nightly levels of 3 aspects of their sleep:
- total sleep time
- sleep onset latency (how long it took to fall asleep at the beginning of the night)
- sleep quality (their own global, subjective assessment of their sleep. A panel of sleep experts convened by the National Sleep Foundation has just determined more precisely what sleep quality means. Read on to find out.)
Predictions and Results
The researchers expected to find a cyclical relationship between affect and sleep. High negative affect and low positive affect would predict greater sleep disturbance. Greater sleep disturbance, in turn, would predict higher negative affect and lower positive affect.
On the whole, data from the study confirmed these predictions. But the findings were also nuanced. Interestingly, affect had a more consistent impact on sleep than vice versa.
How Emotional States Affected Sleep
Positive feelings (joviality, self-assurance, serenity) generally predicted better quality sleep, greater total sleep time, and shorter sleep onset latency. In other words, the more upbeat participants felt during the daytime, the better they slept.
As for the influence of negative affect on sleep, while fear made it harder to fall asleep at the beginning of the night, sadness had the most damaging impact on sleep. Sadness, alone or in combination with low serenity, decreased both sleep quality and total sleep time. Combined with fear, sadness increased sleep onset latency as well. The results suggest that chronic distress—especially sadness—disturbs sleep and could, over time, trigger insomnia and possibly lead to chronic insomnia.
How Sleep Affected Mood
Neither total sleep time nor sleep onset latency affected study participants’ mood the next day. But sleep quality did. After a night of quality sleep, the women reported feeling happier and more confident. And a night of poor quality sleep predicted feelings of malaise and self-doubt. Over time poor quality sleep may lead to decreased positive affect, “which may partially explain how insomnia leads to depression,” the authors conclude.
The take-away here is clear. Don’t allow feelings of sadness or poor quality sleep to persist too long before you look for help. And here’s the National Sleep Foundation’s consensus on the determinants of quality sleep:
- Sleeping at least 85% of the time you’re in bed
- Falling asleep in 30 minutes or less
- Waking up no more than once per night
- Being awake for 20 minutes or less after initially falling asleep
If you have both insomnia and a mood disorder, which came first?