UM study investigates how sleep impacts mood

Researchers at the University of Michigan found that sleep and circadian rhythms play a key role in mental health. While the findings aren't new, they have previously only been demonstrated in small studies or artificial laboratory settings, according to a news release.

The UM study had over 2,500 participants, all of whom were first-year resident physicians. Each participant wore a Fitbit that tracked the time they were awake, and their circadian rhythms, the body's internal clock, and asked them a single question: How was your mood today? Participants could answer the question at any point, and the researchers amassed over 100,000 days of data over the course of two years.

Participants' mood scores were compared to their circadian phase and time awake. Generally, mood peaked around 5 p.m., bottomed out at 5 a.m., and deteriorated the longer a participant stayed awake, the study found.

"You've probably experienced that if you are very tired or stay up very late, this affects your mood," said Danny Forger, senior author of the study and a professor of mathematics and computational medicine and bioinformatics at the UM Medical School. "Your mood also is affected by the internal biological clock, which at certain times of the day tries to get you to be very alert in certain times of the day, tries to get you to be ready for bed."

The biological clock controls circadian rhythms, increasing heart rate at certain times of the day, typically in the middle of daytime hours, and decreasing it at night to prepare people for deep sleep, Forger said. The Fitbits tracked this data in the real world, which correlates to a person's alertness, he said.

"We found an important effect from both the time awake and the state of the circadian clock on mood," Forger said.

Circadian rhythms and sleep also can interact to influence mood, Forger said.

"If you stayed awake for a long time, but your biological clock told your body that it was, say in the middle of the day, you could actually report a better mood," Forger said. "But if you stayed awake for a long time and your biological timekeeping was off, then that's when you really had pretty significant decrements in mood."

The fact that the study was conducted using "real-world" participants made the data "noisy" Forger said. Several other things, such as exercise, can cause a person's heart rate to increase, he explained. Forger's research group developed algorithms to extract circadian data.

"There are a lot of things that went into that algorithm to extract that circadian piece," Forger said. "More important than mathematical algorithms is just the practicality of it. This is one more thing that people could start tracking."

Many people with wearables like Fitbits and Apple Watches already track things like sleep and blood oxygen levels, Forger said. Now, they may want to start tracking their body's daily timekeeping mechanisms.

"My group is interested in developing algorithms that can take data from wearables, or phones, like the Apple Watch Fitbit," Forger said. "For instance, we published an algorithm on how to score sleep from the Apple Watch a number of years ago, it's gotten a lot of attention. We also published an algorithm on how to figure out what time your body thinks it is — the state of this internal biological clock from heart rate."

Forger's research group is developing an app that uses this algorithm on users' data directly from their own wearables. It is still in development but Forger wants to incorporate the study's findings.

People using the app also could contribute to future research by allowing the researchers to use their data anonymously, Forger said. The app, which is called the Social Ribbons App, also comes with safeguards to protect people's data, he said.

"The more data that we get, the more we learn about these things, the more you know, the more we can help people," Forger said.

The study is particularly unique because data collection took place in real-world circumstances, Forger said.

"The field of psychiatry has known that sleep and circadian rhythm play an important role in mental health. However, these findings have only been shown in small samples and in artificial laboratory settings," said Benjamin Shapiro, another lead author of the study and psychiatrist at Dartmouth Health, in the release. "This study generalizes these findings to everyday life across a large number of participants."

It also demonstrates a practical way people can address mental health concerns by changing sleep patterns and adjusting their biological clocks, Forger said. It's particularly important for people who work overnight shifts, those with irregular sleep schedules, and people traveling across time zones, he said.

"What this study could do in terms of health and wellness, is it could alert them to particular times when their biological clock would make them susceptible to the effects of sleep deprivation on mood," Forger said. "People are not very good at assessing what the state of their biological clock is, and they're actually not so good at assessing how well they've slept, and that's why all these wearables are providing a lot more information to people."

It also introduces wearable technology as a new way to explore how biological factors play a role in mental health issues, Forger said.

"Rather than requiring invasive blood draws or temperature monitoring, we are able to obtain similar data from an everyday Fitbit," Shapiro said in the news release. "This opens the door for mental health clinicians to utilize circadian rhythm metrics in everyday clinical practice."

The researchers would like to continue collecting data from different groups, including college students and people who live in other countries to make sure the algorithm works across different populations, Forger said.

One limitation of the study is that it only looks at a generalized model of mood in medical terms, and researchers didn't use validated emotional rating scales or clinical screening tools.

"Individual variation of mood is more complex and dependent on factors such as social dynamics, schedules and temperaments," the press release said.

hmackay@detroitnews.com