- A recent study found that students who fell asleep later at night woke up later in the morning during the winter months.
- The researchers suggest that not getting enough natural light during the day could cause sleep problems at night.
- The findings indicate that exposure to natural light during the day — particularly morning and midday — could improve sleep, even on cloudy winter days.
- Seasonal affective disorder (SAD) may play a role, but more research is still needed.
- To get a good night’s rest, spend time outside during the day, exercise regularly, and maintain a consistent sleep schedule.
During the winter months when the days are shorter and darker, many people spend less time outdoors and don’t get as much natural light. This can affect everything from mood and energy to sleep.
Prior studies indicate that at least 30 minutes of exposure to natural sunlight has a significant impact on the body’s internal clock, promoting more restful sleep.
Now, a recent study revealed some interesting insights about our bodies’ sleep patterns and demonstrates the value of getting outside during the day, even when it’s overcast.
The findings, recently published in the Journal of Pineal Research, show that not getting enough natural light during the day causes problems when it comes to getting quality sleep at night.
“Exposure to daylight is really critical to maintain a healthy circadian system and the sleep hygiene that comes with it,” senior study author Horacio de la Iglesia, PhD, a biology professor at the University of Washington, told Healthline.
How sleep patterns shift with the seasons
For the study, 500 student participants at the University of Washington in Seattle wore wrist monitors that allowed researchers to monitor their sleep patterns throughout the four seasons.
The data show that students were getting about the same total amount of sleep each night despite whether it was winter or summer.
Yet during the winter months, students who fell asleep later at night woke up later in the morning, a time of day in the region when there is less daylight and it’s cloudy outside. On average, they went to sleep 35 minutes later and woke up 27 minutes later on winter school days compared to summer school days.
Because there is less daylight in the winter, the students’ sleep-wake pattern came as a surprise to the researchers. For context, Seattle gets about 16 hours of sunlight on the summer solstice and just over 8 hours of sunlight on the winter solstice.
According to researchers, students stayed up late and slept in because they didn’t get enough exposure to natural light during the winter months.
Getting natural light during the daytime advances the body’s biological clock that times your sleep, de la Iglesia explained. He said this helps make it easier to fall asleep at a reasonable time and wake up in the early morning.
Of course, it’s important to note that a possible limitation of this study is its location, as Seattle is notoriously cloudy. Further studies in different geographical regions are needed to confirm whether natural light exposure can effectively promote sleep.
“We would love to determine how much the delay during the winter months depends on latitude,” de la Iglesia said.
“We are hoping to collaborate with other undergraduate campuses to determine if in more southern latitudes the seasonal differences and specifically the delayed winter timing of sleep go away.”
How daylight affects circadian rhythms
Both daytime and evening light affects the timing of your circadian cycles.
While exposure to daytime light helps promote restful sleep at night, evening light may delay your internal clock and interfere with your ability to fall asleep and get good quality sleep.
“Normally, light is a signal for wakefulness — and light in the evening hours can suppress melatonin and impair sleep,” Dr. Alex Dimitriu, double board-certified psychiatrist and sleep medicine specialist and founder of Menlo Park Psychiatry & Sleep Medicine and BrainfoodMD, told Healthline.
According to the University of Washington study, each additional hour of daytime light was linked to improved circadian rhythms. The authors also noted that bright midday light was more effective for improving sleep than morning light.
“In this study, most interestingly, besides times of sunrise and sunset, the authors noted that midday light of bright intensity plays a very powerful role and correlates with delay in circadian patterns,” Dr. Dimitriu stated.
“The [researchers] also suggest that daily exposure to daylight is key to prevent this delayed phase of the circadian clock and thus circadian disruption that is typically exacerbated in high-latitude winters.”
Does seasonal affective disorder affect sleep?
Seasonal affective disorder (SAD), or major depressive disorder (MDD) with a seasonal pattern, usually occurs during the winter months when there is less sunlight. In some cases, people may experience SAD during the summer months.
Symptoms of SAD may include:
- difficulty sleeping
- weight gain
- social withdrawal
SAD is considered to be the result of light-induced circadian dysregulation, which may lead to emotional changes and mood shifts. As such, Dr. Dimitriu said the power that light has on altering the circadian cycle cannot be overstated.
Still, whether symptoms of SAD could improve from exposure to natural light has yet to be explored by researchers.
Tips to help you sleep better
Whether or not you’re experiencing sleep difficulties due to SAD or are having trouble sleeping in general, there are some proven ways to improve sleep hygiene and get a good night’s rest any time of year.
Be vertical during the day
Since midday light can help adjust circadian rhythm, Dr. Dimitriu said the more you can exaggerate the discrepancy between being asleep versus awake by being more vertical or upright during the day, the better you might fare horizontally at night.
Walking and other forms of physical activity — ideally outdoors — and not lying down immediately after eating may also help you sleep better.
Maintain a consistent schedule
Going to bed at the same time each night and waking up at the same time in the mornings can help train your body’s sleep-wake cycle.
“Sleep loves regularity, so try to keep regular hours, roughly the same on weekends and weekdays,” Dr. Dimitriu said.
Look for signs of fatigue and low mood
SAD is known to be more prevalent in northern and southern latitudes and may affect your mood and disrupt your sleep.
This means it may be a good idea to self-monitor for symptoms of depression, which may present as fatigue, low energy, or lack of excitement or joy, Dr. Dimitriu explained.
If you’re experiencing any symptoms resembling depression and are having difficulty sleeping, you may wish to talk with your doctor or mental health professional for more guidance.
A recent study shows that students who fell asleep later at night woke up later in the morning during the winter months due to a lack of exposure to natural light during the day.
The findings suggest that getting more natural light, particularly in the morning and midday, is essential to maintaining a healthy circadian clock and getting a good night’s sleep.
While seasonal affective disorder (SAD) may also affect sleep during the winter months, the current study did not factor SAD into its analysis.
To improve your sleep patterns in the winter, experts recommend spending more time outdoors, being physically active, and following a regular sleep routine.
If you’re experiencing depression and insomnia, be sure to talk with your doctor about your treatment options.
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