Dartmouth Health leads study showing what it takes to rise and shine

If you want to avoid waking up in a bad mood, try hitting the snooze button. According to a new Dartmouth Health and University of Michigan study, a 5 am wake-up call may be worth sleeping through.

Using Fitbit data from more than 2,500 medical interns over two years, the study uncovers some eye-opening science behind circadian rhythms. Published in the journal PLOS Digital Health, the study found that the interns’ self-reported mood cycles hit their lowest point nearing 5 am and highest point around 5 pm. Staying awake for long periods of time made mood swings more intense throughout the day.

“Our moods naturally cycle from their lowest point in the morning and highest in the evening, and this is independent of sleep deprivation,” said Benjamin H. Shapiro, MD, lead author of the study and psychiatry resident at Dartmouth Health’s Dartmouth Hitchcock Medical Center. “The study suggests someone who’s been awake all night at 5 am should have an even lower mood than if they just woke up at 5 am. However, on a typical day, their mood at 5 am will still be lower than it is in the evening.”

Researchers measured the interns’ continuous heart rate, step count, sleep data and mood scores. They also estimated circadian time and time awake from minute-by-minute wearable heart rate and motion measurements. As part of the Intern Health Study, a multicenter study across the United States involving first-year physicians, the interns also completed a daily assessment consisting of a single question: How was your mood today?

The data from the mood scores were then plotted against their circadian phase and their time awake. In addition to learning more about biorhythms, the study also underlines the value of wearables as a means of tracking mood disorders.

“Instead of resorting to invasive blood draws or body temperature monitoring, clinicians are able to obtain similar data from an everyday Fitbit,” Shapiro says. “In mental health care settings, this opens the door for utilizing circadian rhythm metrics in everyday clinical practice.”

Our internal clocks seem to be naturally set for just how bright-eyed and bushy-tailed we might expect to feel at any given time of day.

“The study highlights the significant role our body’s clock plays in mood and introduces wearable technology as an exciting new way to explore these factors in mental health issues,” said Daniel B. Forger, PhD, senior author of the study and a professor of mathematics and computational medicine and bioinformatics at the University of Michigan Medical School.

Although the study only looked at a generalized model of mood in medical terms, individual variation of mood is more complex. Other factors, such as social dynamics, schedules, and temperaments, all play a role in mental health. In addition, this study had few participants who stayed awake more than 18 hours during a day. Furthermore, the researchers did not use validated emotional rating scales such as the Depression Anxiety Scale or clinical screening tools. Still, the findings seem to suggest we shouldn’t lose sleep if we’re waking up on the wrong side of the bed