An unexpected way to fall asleep earlier and improve sleep has been revealed

Scientists have found that the more time a person spends in the morning sun, the earlier they go to bed and the better they sleep. The results of the study have been published in the journal BMC Public Health.

Researchers surveyed 1,762 adult residents of one of Brazil's regions — and discovered a striking pattern. Every additional half hour spent in the sun before 10 a.m. shifted the moment of falling asleep by approximately 23 minutes earlier. On average, participants slept more than seven hours per night, and those who were more frequently exposed to morning light reported improvements not only in sleep duration but also in its subjective quality.

Interestingly, daytime light — from 10 a.m. to 3 p.m. — had virtually no effect on the time of falling asleep. This suggests that the human biological clock is primarily calibrated by morning and evening light rather than midday light. Sun exposure after 3 p.m. produced a noticeably weaker effect — approximately a 19-minute shift for the same half hour of light.

A special brain region is responsible for calibrating circadian rhythms — the suprachiasmatic nucleus, which regulates the production of the "sleep hormone" melatonin based on light signals. This is precisely why morning light is able to "reset" the internal clock to an earlier time. Disruptions in circadian rhythms are associated with problems related to sleep, mood, and metabolism, meaning morning sun could prove to be a simple and accessible tool for correcting them.

The authors of the study note a number of limitations: the data are based on self-reports, without the use of objective instruments and without accounting for screen light exposure, and data collection took place during the period of COVID restrictions, which may have affected sleep through stress and isolation. Nevertheless, the results confirm a simple recommendation — spend more time in morning light if you want to fall asleep earlier and sleep better.