Friend or Phone: How Light Affects Your Metabolism
By Natalie Sanchez-Lazo
Exposure to blue light, or any light for that matter, at irregular times has become an increasingly pressing issue in modern day life. Whether it’s leaving a light on or checking your email right before bed, night light is a nearly universal experience. However, it’s not very often that we take a second to consider how this is affecting our health. At first, it may seem rather obvious that it keeps us awake at night when we should be sleeping, leading to sleep deprivation or that blue light exposure at irregular times might be harming your eyes. But is it possible that your metabolism might be affected as well?
Metabolism is the combination of processes that allow your body to convert the food and drinks you consume into energy. These processes are endogenous, meaning that they happen naturally in your body without intervention. While your stomach and liver can’t see the blue light that you’re looking at night, your eyes sure can. Your eyes perceive light through the rods and cones in the back of your retinas. In particular, blue light causes your melanopsin receptors to send signals to the brain’s suprachiasmatic nucleus, also known as the “master clock” of your circadian and diurnal rhythms.
Circadian rhythms are your body’s patterns of eating, sleeping, and everything in between that happens in a roughly 24 hour cycle. These happen naturally, almost regardless of your environment. On the other hand, diurnal rhythms require signals from the environment, also known as zeitgebers, to continue their endogenous processes (5). The circadian system is made up of one master clock in the suprachiasmatic nucleus and several smaller clocks throughout the body (5). They communicate with each other very regularly to maintain one’s circadian rhythm.
As mentioned previously, light at any point of the day sends signals through your eyes (melanopsin receptors) to your brain (suprachiasmatic nucleus and other areas involved in metabolism, 1). Light signals a need for wakefulness, but not just to your eyes. The rest of your body has to be awake with your eyes, which is where the rest of the metabolism gets involved. In order to be awake, your sympathetic nervous system (which is in charge of fight/flight/freeze, but is mostly used for wakefulness) needs to be at least a little active. In order for sympathetic activity to arise, your body must convert the food and drinks you consume into energy, and it does so through glucose and its related bioactive molecules.
Whenever you eat foods with carbohydrates or sugar, your blood glucose (glycemic) levels rise. Insulin has a lot of functions in the body, but the function that it is best known for is reducing glycemic levels. Blood glucose is one of the body’s main sources of energy, if not the main source of energy. In order to stay awake your body needs to have a sufficient amount of it.
Back to the original question: is light at night bad for you? Blue light specifically signals your melanopsin receptors to signal your suprachiasmatic nucleus to be awake. The suprachiasmatic nucleus (along with other members of the hypothalamus) signal your body to keep the glycemic levels going. Normally this is good, and one would want this to happen during the day, but disrupting your circadian rhythm, including your sleeping patterns, can have detrimental effects. In terms of the body, it takes away from your body’s resources during the day. Even for short periods of time, consistent blue light exposure at night alters your glycemic levels the following morning (2). Light exposure at night as a whole isn’t good either, firstly because sympathetic activity includes a raise in heart rate (2). Additionally, it reduces your slow wave sleep (when the brain & body repair themselves), total sleep time, and the overall efficacy of your sleep (2). When combined with sleep deprivation, light exposure at night leads to higher levels of glucose after a meal, making it harder for insulin to have its effect, and slowly builds into insulin resistance (the defining factor for type 2 diabetes, 2). In a large cross sectional study with over 100,000 women, brighter light at night was associated with a higher BMI (body mass index), waist circumference, and waist-to-hip ratio. It’s important to note that BMI doesn’t necessarily correspond to metabolic health, but in this context it fits somewhat well with the general association between light at night and decreased metabolic health.
So I think it’s safe to say that light at night is bad.
But there is hope! A study by Nagai et. al has found that blue light blockers notably reduced fasting plasma glucose and insulin resistance measurements (3)! Additionally, it also increased the sleep quality of the participants (3)! Yellow filters have also been proven to be effective and reduce the stress put on your eyes (Lledó et. al)!
It’s really about doing the best with what you have. If you’re scared of the dark and sleeping with all the lights off won’t let you sleep, then the effects of light during sleep are minimal in comparison to no sleep at all. Our blue-light devices aren’t all evil either, unless they’re keeping you up at night and distracting you from going to bed at a reasonable time. None of us are perfect, so make the changes that you can, if you so wish!
Works Cited
Lledó, Victoria Eugenia et al. “Yellow Filter Effect on Melatonin Secretion in the Eye: Role in IOP Regulation.” Current eye research vol. 44,6 (2019): 614–618. doi:10.1080/02713683.2019.1570276
1. Masís-Vargas, Anayanci et al. “Blue light at night acutely impairs glucose tolerance and increases sugar intake in the diurnal rodent Arvicanthis ansorgei in a sex-dependent manner.” Physiological reports vol. 7,20 (2019): e14257. doi:10.14814/phy2.14257
2. Mason, Ivy C et al. “Light exposure during sleep impairs cardiometabolic function.” Proceedings of the National Academy of Sciences of the United States of America vol. 119,12 (2022): e2113290119. doi:10.1073/pnas.2113290119
3. Nagai, Norihiro et al. “Suppression of Blue Light at Night Ameliorates Metabolic Abnormalities by Controlling Circadian Rhythms.” Investigative ophthalmology & visual science vol. 60,12 (2019): 3786–3793. doi:10.1167/iovs.19–27195
4. Opperhuizen, Anne-Loes et al. “Light at night acutely impairs glucose tolerance in a time-, intensity- and wavelength-dependent manner in rats.” Diabetologia vol. 60,7 (2017): 1333–1343. doi:10.1007/s00125–017–4262-y
5. Poggiogalle, Eleonora et al. “Circadian regulation of glucose, lipid, and energy metabolism in humans.” Metabolism: clinical and experimental vol. 84 (2018): 11–27. doi:10.1016/j.metabol.2017.11.017
6. Ursino, Gloria, and Roberto Coppari. “Insulin under the influence of light.” Swiss medical weekly vol. 150 w20273. 21 Jun. 2020, doi:10.4414/smw.2020.20273
Pictures Works Cited
Biologydictionary.net Editors. “Suprachiasmatic Nucleus.” Biology Dictionary, Biologydictionary.net, 15 Mar. 2018, https://biologydictionary.net/suprachiasmatic-nucleus/.
Memorial Sloan Kettering Cancer Center. “Do Cell Phones Cause Cancer?” Memorial Sloan Kettering Cancer Center, 20 May 2019, https://www.mskcc.org/news/do-cell-phones-cause.
