Sleeping for eight hours may not be enough to protect mental health if bedtimes and waking times vary widely, according to a new study linking irregular sleep schedules with more severe symptoms of anxiety, depression and loneliness.

Researchers from the University of California, San Francisco, and UC San Diego analysed sleep records from 22,894 adults in research published in Scientific Reports on 12 November 2026. Participants wore Oura smart rings during a study conducted in 2020, with sleep data covering periods of up to seven months.

They also completed monthly questionnaires about their mental health. Researchers used the responses to assess whether participants reporting more severe symptoms had less consistent sleep schedules.

Depression and Anxiety Symptoms Differ by Sleep Schedule

The researchers used a sleep regularity index scored from zero to 100, with higher figures indicating more consistent sleep and waking patterns. People reporting few or no depressive symptoms averaged approximately 84, compared with 83 for mild symptoms, 81 for moderate symptoms and 75 for severe symptoms.

Participants with severe anxiety averaged 79, against 84 among those whose anxiety scores were within normal limits, as per a report by UCSF.

Loneliness followed a similar pattern, although the difference was smaller. People reporting elevated loneliness averaged a sleep regularity score of about 82, compared with nearly 84 among other participants. The link between irregular sleep and more severe symptoms remained in statistical analyses accounting for age, sex and average sleep duration.

The seven-day analysis showed a similar overall pattern, although the differences between participants with normal anxiety levels and those with mild or severe anxiety were not statistically significant. The longer observation period generally revealed stronger associations, suggesting that extended monitoring may provide a more stable measure of sleep regularity.

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Why Eight Hours May Not Tell the Whole Story

A regularity score measures how consistently someone sleeps at similar times, not the total hours spent asleep. Researchers said a person scoring around 84 might shift their sleep and waking times by roughly an hour between days, while a score around 75 could reflect shifts closer to 90 minutes.

Changing sleep schedules can affect the body's circadian rhythm, which helps regulate sleeping, alertness and other daily functions.

Separate research involving about 100,000 UK Biobank participants also linked irregular sleep timing with a greater likelihood of later mental health conditions, including depression and bipolar disorder, according to a report by UK Biobank.

That association was reported even among people sleeping the recommended seven to nine hours. The findings suggest adequate duration and consistent timing are distinct parts of sleep health.

Anxiety and Depression Can Disrupt Sleep Too

The new American-led research cannot establish which comes first. Anxiety and persistent worrying can make it difficult to fall asleep or stay asleep, while mental health symptoms may also interfere with regular sleep routines.

The researchers also cautioned that their sample consisted largely of middle-aged, White wearable-device users in North America and Europe, limiting how widely the findings can be applied.

Keeping Sleep Times Consistent

The National Health Service (NHS) recommends going to bed and waking up at around the same time each day, while allowing enough time for sleep. Most adults need between seven and nine hours of sleep, according to the agency, although individual requirements vary.

Researchers say controlled studies are still needed to determine whether making sleep schedules more regular directly reduces symptoms of anxiety or depression.

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