Nighttime light may disrupt sleep in people with schizophrenia

Sleep problems are common in people with schizophrenia and can worsen quality of life, psychiatric symptoms, cognition and daily functioning. Nighttime light is known to interfere with normal sleep and circadian rhythms in the general population, but its relationship with sleep in schizophrenia had not been examined using both objective and subjective measures.

The new study provides the first evidence that greater nighttime light exposure is associated with poorer objectively measured sleep in outpatients with schizophrenia. The authors emphasize that the findings should be viewed as an association rather than proof of cause and effect, pending prospective intervention studies.

The researchers analyzed 225 adult outpatients with schizophrenia who took part in the Light Exposure and Neurobiology in Schizophrenia (LENS) study. Participants wore a wrist actigraphy device continuously for seven days to measure sleep and light exposure.

A portable photometer placed beside the bed independently measured ambient nighttime illuminance, while a sleep diary recorded bedtime and rising time. Subjective sleep quality was assessed using the Pittsburgh Sleep Quality Index.

The findings were published in the journal Psychiatry Research.

The study was led by Dr. Yuichi Esaki and Ryota Miyake, a student, together with Dr. Nakao Iwata and Dr. Tsuyoshi Kitajima from the Department of Psychiatry, Fujita Health University School of Medicine, Aichi, Japan, and Dr. Kiyoshi Fujita from the Department of Psychiatry, Okehazama Hospital, Aichi, Japan. Median nighttime illuminance was 1.4 lux by actigraphy and 4.1 lux by photometer.

After accounting for factors including age, sex, smoking, body mass index, psychiatric symptoms, daytime light, sleep timing, day length and medications, people in the highest nighttime-light group had 10% lower sleep efficiency, 55.6 minutes less total sleep, longer sleep onset and 31 minutes more wakefulness after sleep onset than those in the lowest-light group. Higher blue-light exposure showed similar associations.

“Our findings suggest that even relatively low levels of nighttime light may be linked to measurable sleep disruption in people with schizophrenia,” Miyake said.

Importantly, the relationship was seen in objective sleep measures but not in the Pittsburgh Sleep Quality Index. This difference may indicate that some patients experience poorer sleep without fully recognizing it or may reflect the different measurement periods: Subjective sleep was assessed over the previous month, whereas actigraphy and light exposure were measured prospectively for seven days.

The findings point to a potentially simple way to support sleep management. Reducing unnecessary light in bedrooms could provide a low-cost, nonpharmacological approach alongside existing treatment, although the cross-sectional design means the study cannot show that nighttime light causes poor sleep.

“Optimizing the nighttime light environment could become an important part of sleep hygiene if future longitudinal and intervention studies confirm these findings,” Miyake said.

Such research could eventually guide lighting practices in homes, hospitals and residential facilities, potentially supporting healthier sleep and reducing the need for additional sedating medication. Future trials could test whether darker bedrooms improve sleep, symptoms, daytime functioning and overall quality of life in this population.

Overall, the study highlights nighttime light as a modifiable environmental factor that deserves greater attention in sleep care for people with schizophrenia.

Who’s behind this story?

Swati Mestri

Swati Mestri holds a bachelor’s degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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