Exposure to Daylight Predicts When You'll Fall Asleep, Study Shows

A new study shows a correlation between the seasons and shifts in sleeping patterns.

In the winter months, research participants went to sleep later in the evening and woke up later in the morning, as compared to the summer months.

In line with earlier research, the team behind the new study thinks that less light exposure during the day can cause our body clock to shift and make us less ready for sleep when night comes around.

Horacio de la Iglesia is a Biologist at the University of Washington in Seattle.

If you don't get enough exposure to light during the day when the sun isn't shining, that delays your clock and causes you to sleep later.

The data was gathered from wrist monitors over the course of three years. The monitors looked at both sleep activity and exposure to light.

Students went to bed 35 minutes later in the winter and woke up 27 minutes later in the summer.

Given Seattle's high latitude, the numbers were somewhat surprising.

Light exposure has different effects on the clock at different times. Light during the day is more likely to cause you to sleep earlier, while light at night is more likely to keep you awake.

Each hour of daytime light exposure, even on cloudy days, shifted the students' melatonin levels by 30 minutes. The light pushed these phases back by 15 minutes.

De la Iglesia says it's the push-and- pull effect. Since students weren't getting enough daytime light exposure in the winter, their melatonin levels were delayed compared to summer.

Our rhythms run on a cycle of about 24 hours. Our age, diet, and technology use can affect the clock's running.

Since the invention of the electric lightbulb, artificial light has played a role in the effects of light exposure during the day and night. Activities are not limited by the hours of daylight anymore.

The results go beyond students. Getting to bed at the same time each night is one of the benefits of more exposure to natural light during the day.

De la Iglesia says that many people live in cities and towns with lots of artificial light and lifestyles that keep them indoors during the day.

The study shows that we need to get out in the morning to get that light exposure. Artificial lighting and screen time can make it hard to sleep in the evening.

The journal of pineal research has published the research.