True or False: Getting more sunlight during the day helps you sleep better
Updated: Oct 28, 2022
Have you ever wondered why you may not be sleeping as well as you should? Do you spend most of your day inside? Or under artificial light? These are questions to ask yourself if you feel like you need improvement in the quality of your sleep.
Most of us know a little about circadian rhythms or have heard the term before. Circadian rhythms synchronize our body with the 24-hour day via the sunlight. Sunlight plays a prominent role in when we are awake (and have periods of activity) versus when we rest and sleep. Humans have a “central clock” called the suprachiasmatic nuclei (SCN), which regulates circadian rhythms (Blume et al. 2019). However, there is more than just a biological central clock regulating circadian rhythms. The environment sends input and output to the body to make our circadian rhythms regular. The SCN gets information from our retina about how much light it receives from the environment and then sends this information to the rest of the body. When our eyes detect sunlight in the retina, the retinohypothalamic tract is used to send the information to the SCN (Duffy et al. 2009). The neurons in the SCN use the light input to send information to areas like the pineal gland, where the sleep hormone melatonin is produced. During light exposure, the production of melatonin decreases, while during darkness, melatonin levels increase.
As most of us know, melatonin supplements are very common to improve sleep - but maybe introducing more sunlight time into your day will help improve your sleep without the supplemental melatonin. This may be possible since the SCN also sends signals to the raphe nuclei, producing serotonin (Blume et al. 2019). Serotonin is sometimes referred to as a “Happy Hormone” as it mediates mood, sleep and sexual desire. When serotonin levels rise, the raphe nuclei communicate with the hypothalamus and cortex to tell the body to feel more awake, like when you wake up in the morning. What most don’t realize is that serotonin is a precursor of melatonin. That is, serotonin is used to synthesize melatonin (in the pineal gland). Without enough sunlight during the day, we produce less serotonin and are then more prone to the suppression of melatonin levels at night and a shift in our circadian rhythms, affecting our sleep (Blume et al. 2019). Even just 5 minutes of light exposure can shift your circadian rhythm. Hence, sunlight is needed for the SCN to synchronize all your normal bodily functions to its circadian rhythms
More prolonged exposure to daylight can cause you to sleep earlier and longer. But, it is important to get sunlight earlier in the day rather than later.
Getting sunlight later in the day showed negative effects on staying awake later, waking up from sleep, and sleep quality. This is likely because we are most sensitive to light during the night time as our biological clock is set to be asleep (Duffy et al. 2009).
A study was done on how artificial bedside lights could affect sleep quality (Obayashi et al. 2018). This study was done on elderly participants, and the light was turned on 2-hours before the participants woke up. The results of this study proved that increased light exposure correlates with increased sleep disturbance. In other words, getting light at the wrong time of day - in this case, too early - significantly decreases sleep quality.
Another study investigated the consequence of light therapy on sleep problems in older adults (Duzgun et al. 2017). This study found that direct exposure to sunlight during 8-10 am for five days was effective in significantly improving sleep quality. The current evidence suggests that increased exposure to direct sunlight during the day may improve sleep quality.
We need sunlight to go to bed at a reasonable time, sleep longer, and have a better quality of sleep. Hence, sunlight is beneficial for better sleep. If you have trouble sleeping, this is your prompt to spend more time outside in the sunlight.
Written by Ahdeesh Singh, BS and edited by Aldrin V. Gomes, PhD
Blume, Christine, et al. Effects of Light on Human Circadian Rhythms, Sleep and Mood. Somnologie, vol. 23, no. 3, 2019, pp. 147–156.
Duffy, Jeanne F., and Charles A. Czeisler. Effect of Light on Human Circadian Physiology. Sleep Medicine Clinics, vol. 4, no. 2, 2009, pp. 165–177.
Düzgün, G., Durmaz Akyol A. Effect of Natural Sunlight on Sleep Problems and Sleep Quality of the Elderly Staying in the Nursing Home. Holist Nurs Pract. 2017 vol. 31, no. 5, 2017, pp. 295-302.
Obayashi, K., Yamagami, Y., Kurumatani, N., Saeki, K. Pre-awake light exposure and sleep disturbances: findings from the HEIJO-KYO cohort, Sleep Medicine, vol. 54, 2019, pp. 121-125.