Why Exposure to Light While You Sleep is Unhealthy

 
Medically reviewed by
Dacelin St Martin, MD
Triple board-certified in Sleep Medicine,
Internal Medicine, and Pediatrics.

 
 
The Research | How Does Light Affect Sleep? | How To Optimize Your Sleep Environment

Overview

You may have noticed that you sleep better in a dark room than in a brightly lit room. 

It’s probably the same for everyone. However, getting a completely dark sleep environment can sometimes be challenging, especially if you live in a buzzing urban city with brightly lit streets. 

This article will highlight an extraordinary study that links sleeping in a lit environment to health troubles. It will also explain how light affects your sleep and provide tips on optimizing your sleep space for healthy sleep.

The Research

Experts from the Northwestern University Feinberg School of Medicine in Chicago have published a study that evaluates the connection between light exposure during sleep and an increased risk of developing health problems.^[1] 

The study serves as a cautionary tale for individuals who live in urban cities, where light is typically ubiquitous. According to the findings of this study, sleeping in any kind of light, even dim light, can increase the risk of developing chronic medical conditions like diabetes, hypertension, and obesity.^[1] 

According to Dr.Minjee Kim a renowned neurologist and leading author of the study, “Whether it’s a smartphone, a TV left on overnight, or excessive street lights in a large city, we are surrounded by an abundance of artificial light sources that are available 24 hours a day.”^[1]

Although animal studies had linked light exposure to poor health, Dr. Kim noted that there was a lack of information regarding the patterns of light exposure in older adults. 

“Since older persons are already at a higher risk for cardiovascular illness, we sought to determine how often they are exposed to light at night and if light exposure during sleep raises the risk for cardiovascular illnesses,” she said. 

It’s essential to note that light exposure during sleep is dangerous to everyone, regardless of age.^[1] 

Another study by Dr. Kim’s colleagues revealed that a single night of exposure to light could cause an increase in heart rate and raise blood sugar levels in young, healthy individuals.^[2]

How Does Light Affect Sleep?

Light can affect your sleep in many ways. Here are some ways it can negatively impact your sleep:

• Alteration of The Circadian Rhythm: The circadian rhythm regulates many bodily functions, including sleep. This 24-hour internal clock is controlled by a part of the brain called the suprachiasmatic nucleus (SCN), which is heavily influenced by environmental cues like light.^[3] Experts believe that light is the most significant regulator of the circadian rhythm.When rays of light enter the eye, it is detected by special cells in the retina, which relay this information to the brain, where it is interpreted as data about the time of day.^[3] The brain then regulates one’s sleep and other bodily functions in synchrony with the presence of environmental light. It means that the brain instructs your body to sleep when there is little or no environmental light. It also makes you alert and active when it is daytime. Artificial lights from mobile devices, neon lights, and television can significantly alter one’s circadian rhythm.^[4] It makes it difficult for the brain to delineate night from day and therefore hampers one’s sleep.^[5]
• Decreased Melatonin Production: Melatonin is the hormone responsible for initiating sleep and maintaining sleep.^[6] It’s heavily influenced by light. Regular melatonin production helps to maintain a normal circadian rhythm and promotes a steady sleep-wake schedule. The pineal gland produces melatonin in the brain in response to darkness.^[6] The presence of light in your sleep environment can inhibit the production of melatonin by your body, disrupt your sleep-wake cycle, and lead to significant sleep abnormalities.
• Disrupt Sleep Architecture: Light can also influence the architecture of one’s sleep. Typically, a person transits the four stages of sleep 4 – 6 times before waking up.^[7]Each cycle could last between 70 and 120 minutes. Exposure to light during sleep can disrupt the transition from one sleep stage to another, reduce time spent in deep sleep, shorten total sleep duration, and ultimately lower sleep quality.
• Activation of the Sympathetic Nervous System: Experts believe that exposure to light activates the sympathetic nervous system.^[8] This system is responsible for fight and flight responses to danger. It keeps you alert and agitated, making it challenging to initiate and maintain sleep.
  
  

How To Optimize Your Sleep Environment

Quality Sleep is crucial to your health. An optimized sleep environment can help improve your sleep quality and duration. Here are some ways you can optimize your sleep environment for better sleep:

• Keep light Out of your Bedroom: Ensure your bedroom is devoid of any light source before attempting to get some shuteye. Dark-colored curtains can help you to block out most of the light from outside, creating a darker atmosphere. 
• Use sleep-friendly Light: Experts believe sleeping in a dark room is the best way to sleep. However, if you need some illumination in your room, ensure you use colored lights that are not harmful to your sleep. Experts recommend amber/red colored light because they are less likely to throw off your circadian rhythm and hurt your sleep, unlike blue light.^[9] 
• Keep electronic gadgets out of your sleep environment: Light from your mobile devices and other electronics can impair sleep.^[10] Always make sure to keep your gadgets away when it is sleep time.

References:

1. Kim, Minjee, et al. “Light at Night in Older Age Is Associated with Obesity, Diabetes, and Hypertension.” OUP Academic, Oxford University Press, 22 June 2022, https://academic.oup.com/sleep/advance-article-abstract/doi/10.1093/sleep/zsac130/
2. Mason, Ivy C. Light Exposure during Sleep Impairs Cardiometabolic Function | PNAS. https://www.pnas.org/doi/10.1073/pnas.2113290119.
3. Dodson, E. R., & Zee, P. C. (2010). Therapeutics for Circadian Rhythm Sleep Disorders. Sleep medicine clinics, 5(4), 701–715. https://doi.org/10.1016/j.jsmc.2010.08.001
4. Chang, A. M., Santhi, N., St Hilaire, M., Gronfier, C., Bradstreet, D. S., Duffy, J. F., Lockley, S. W., Kronauer, R. E., & Czeisler, C. A. (2012). Human responses to bright light of different durations. The Journal of physiology, 590(13), 3103–3112. https://doi.org/10.1113/jphysiol.2011.226555
5. Jagannath, A., Taylor, L., Wakaf, Z., Vasudevan, S. R., & Foster, R. G. (2017). The genetics of circadian rhythms, sleep and health. Human molecular genetics, 26(R2), R128–R138. https://doi.org/10.1093/hmg/ddx240
6. Masters, A., Pandi-Perumal, S. R., Seixas, A., Girardin, J. L., & McFarlane, S. I. (2014). Melatonin, the Hormone of Darkness: From Sleep Promotion to Ebola Treatment. Brain disorders & therapy, 4(1), 1000151. https://doi.org/10.4172/2168-975X.1000151
7. Patel, A. K., Reddy, V., & Araujo, J. F. (2020, April). Physiology, Sleep Stages. StatPearls Publishing. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK5261
8. Waxenbaum, Joshua A. Anatomy, Autonomic Nervous System. https://www.ncbi.nlm.nih.gov/books/NBK539845/.
9. Noguchi, H., & Sakaguchi, T. (1999). Effect of illuminance and color temperature on lowering of physiological activity. Applied human science: journal of physiological anthropology, 18(4), 117–123. https://doi.org/10.2114/jpa.18.117
10. Exelmans, L., & Van den Bulck, J. (2017). Bedtime, shuteye time and electronic media: sleep displacement is a two-step process. Journal of sleep research, 26(3), 364–370. https://doi.org/10.1111/jsr.12510