An app that reads your sleep, activity and light through a Fitbit wristband may keep depression and bipolar episodes from returning.
That is the finding of a year-long clinical trial published in the American Journal of Psychiatry in June 2026.
Researchers followed 93 adults with major depressive disorder or bipolar I or II across five hospitals in South Korea.
All had been well for at least two months, but had lived through a mood episode in the previous two years.
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Half received the Circadian Rhythm for Mood app, called CRM. The other half received a look-alike sham.
Neither the participants nor their treating clinicians knew who had which.
Over the year, the sham group had about 3.4 times as many recurrences as the app group.
Your daily rhythm
The CRM app pairs with a Fitbit wearable to gather steps, heart rate and sleep timing. The phone's own sensor measures ambient light.
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From that data, it calculates a circadian stability score.
Circadian stability means how regular your body clock stays from day to day.
It reflects when you fall asleep, when you wake, when you move around, and when you get bright light.
The app then delivers tailored advice for steadying the rhythm and sends a three-day mood forecast built with machine learning.
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If the score starts to slip, the app pings the user with an alert.
Why body-clock timing matters for mood
Circadian rhythms are the roughly 24-hour cycles that govern sleep, hormones and alertness.
An editorial in BJPsych International noted that well-synchronized rhythms are fundamental for mental health, and that modern living can push those rhythms out of sync.
Mood disorders often disrupt sleep and daily routines. Irregular sleep timing can be an early warning of an incoming depressive or manic episode.
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Late sleep patterns have also been linked to a heavier mental health burden than morning schedules.
In the CRM trial, the sham group logged 53 recurrent mood episodes across the year. The app group logged 15.
A conservative reanalysis that counted dropouts as failures still showed a benefit, though smaller.
The trial did not eliminate relapse. The authors also noted they could not fully capture medication changes during the study.
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Even so, the size of the effect stood out for a smartphone tool.
The researchers wrote that combining active input with passive tracking allows real-time monitoring and personalized feedback that may help patients better manage their symptoms.
The CRM app was tested only in a Korean hospital population, and larger trials in other countries would be needed before doctors can recommend it as a standard tool.
Anyone considering a mood-tracking app should discuss it with their mental health clinician before changing any current treatment.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.