Last month we talked about the relationship of sleep to cortisol. This month is about the “sleep hormone” melatonin, which is produced by the brain during sleep. Levels of this hormone peak in the middle of the night, and decrease rapidly when you are exposed to light[1]. Changing levels of melatonin in your body help regulate functions related to light and dark cycles like metabolism, immunity and reproduction[2].
Melatonin is a hot topic among night owls, shift workers and jet setters because of its reputation for promoting sleep. In fact, most people have only heard of this hormone in relation to sleep. But let’s be clear: melatonin does NOT cause sleep.
Modern Man vs. Caveman
Melatonin is secreted when there is darkness. For our ancestors, that was when the sun went down. Back then the sun went down, melatonin was secreted, and they went to sleep. Because its production preceded sleep it makes sense why one would think to take melatonin before bed. However, melatonin cannot be produced in the presence of light, even artificial light[3]. For us, darkness has nothing to do with the sun. Now the sun goes down, we turn the lights on, we watch TV, we take our phones and computers to bed, and then go to sleep. Closing our eyes is the first time our brain registers full darkness[4]. Modern day melatonin production follows sleep, it does not cause it.
While this beneficial hormone is crucial for regulating multiple systems in our body, the misconception that it causes sleep and the resulting supplementation is doing more harm than good.
For our caveman ancestors, daylight was the only thing that would depress melatonin secretion. But artificial light is the light we turn on once the sun goes down, and it is just as effective at suppressing this hormone as the sun2. The most egregious artificial light and melatonin suppressor is blue light, which comes from electronic screens. With kids staying up later and having phones and electronics at younger ages, this artificial and blue light is affecting them as well.
The Repercussions
One of the most alarming trends of our younger generations is early sexual development. This is fairly blamed on synthetic hormones in our food supply, but we should also point out the prolonged period of suppressed melatonin that naturally precedes puberty[5][6][7][8][9]. We want to make sure we don’t mimic this phenomenon by artificially lowering melatonin on our kids with over-exposure to indoor light and electronics and trick the body into a precocious puberty. Since light decreases its production and sleep increases it, this means limited screen time and an early bedtime for children is crucial for healthy puberty.
Keep in mind, melatonin doesn’t just affect sexual development. It affects adult sexual function as well. It suppresses sex hormone production[10]. This makes sense because melatonin production, once you close your eyes, helps ensure it’s time for sleep, nothing else. It also makes sense to our seasonal breeder biology. Melatonin is lowest in the summer when nights are short, helping to assure sexual function is at its peak nine months before spring, which was historically the most advantageous time to have a baby[11]. While natural melatonin in the proper rhythm is beneficial, supplementation can be detrimental to sexual function. Considering it is most often recommended 30 minutes before bedtime, it might as well be the anti-“little blue pill.”
What about Supplements?
After learning that it suppresses sex hormone production, I’m sure melatonin supplements are much lower on your “to try” list. But in case they are still on your sleepless mind or your nightstand, remember that melatonin does not cause sleep and no amount of supplemental melatonin will counteract the brightness of artificial and blue light. For those who still struggle with sleep, next month’s blog will focus on safe and natural alternatives to this misunderstood “sleep hormone” and complete the series with recommendations on what you can do to support healthy sleep. For now, go to bed early, turn off the lights, don’t supplement with melatonin, and make sure your kids do the same.
Written by Lindsea Willon, MS, NTP
References
[1] Macchi, M. M., & Bruce, J. N. (2004). Human pineal physiology and functional significance of melatonin. Frontiers in neuroendocrinology, 25(3), 177-195.
[2] 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).
[3] Figueiro, M. G., Wood, B., Plitnick, B., & Rea, M. S. (2011). The impact of light from computer monitors on the melatonin levels in college students. Biog Amines, 25, 106-116.
[4] Wiley, T. S. (2016). Lights out: sleep, sugar, and survival. Atria Books.
[5] Crowley, S. J., Acebo, C., & Carskadon, M. A. (2012). Human puberty: salivary melatonin profiles in constant conditions. Developmental psychobiology, 54(4), 468-473.
[6] Cavallo, A. (1992). Plasma melatonin rhythm in normal puberty: interactions of age and pubertal stages. Neuroendocrinology, 55(4), 372-379.
[7] Waldhauser, F., Boepple, P. A., Schemper, M., Mansfield, M. J., & Crowley Jr, W. F. (1991). Serum melatonin in central precocious puberty is lower than in age-matched prepubertal children. The Journal of Clinical Endocrinology & Metabolism, 73(4), 793-796.
[8] Cavallo, A. (1993). Melatonin and human puberty: current perspectives. Journal of pineal research, 15(3), 115-121.
[9] Murcia, G. J., Muñoz, H. A., Molina, C. A., Fernández, G. J., Narbona, L. E., & Uberos, F. J. (2002). Puberty and melatonin. Anales españoles de pediatría, 57(2), 121-126.
[10] Claustrat, B., & Leston, J. (2015). Melatonin: Physiological effects in humans. Neurochirurgie, 61(2), 77-84.
[11] Srinivasan, V., Spence, W. D., Pandi-Perumal, S. R., Zakharia, R., Bhatnagar, K. P., & Brzezinski, A. (2009). Melatonin and human reproduction: shedding light on the darkness hormone. Gynecological Endocrinology, 25(12), 779-785.
