In the beginning, there was darkness.
And the first thing that happens, the first act of creation in one of the oldest books in the world, is light.
“Let there be light.”
Not the sun. Not the stars. Those don’t arrive until the fourth day. Light comes first, on its own, before anything we would think of as a source of it.
Genesis isn’t the only place this shows up. The Quran calls God the light of the heavens and the earth. Hindu scriptures speak of a light of lights. Sikh teaching describes a divine light that is present in all of creation.
Different cultures. Different centuries. Different languages. Light at the center of all of them.
I was pondering this one day in the shower, and that is how this episode came about.
I have spent more than thirty years in exam rooms, labor rooms, operating rooms, and at bedsides. When a woman says, “I can’t sleep,” I know how that conversation usually goes. It rarely starts with light.
Genesis started with light. Medicine starts with pills.
This week I want to talk about that gap, and about what we might be missing on the other side of it.
Why I care about this
I’m Seanna Aker. I’m a registered nurse, a mom of three, and the founder of The Sleep Nurse, where I teach midlife women how to sleep again. Sleep is my life’s work.
For almost twenty of my thirty-plus years as a nurse, I worked night shift, and my own sleep fell apart. I was a night shift nurse and a mom, trying to balance everything. I couldn’t nap before a shift because there was dinner to make and everything else to do. My husband was in grad school at the time. By the time I drove home the next morning, around eight or eight-thirty, I had often been awake close to twenty-four hours. I did this week after week, year after year.
So I leaned heavily on medication. I took Ambien. I took melatonin. I took Benadryl. They helped, but later I realized they were only sedating me. I wasn’t getting restorative sleep. It took about four years for the fog to lift, and even then I was not sleeping well. I still relied on supplements and outside sources to get to sleep.
What changed for me wasn’t a new pill. It was learning how light, routine, and rhythm shape my biology. It sounds simple, and it is not something they taught us in nursing school. We were taught about pills. You have pain, what’s your pain score, here’s a pill. You can’t sleep, here’s a pill. We learned biology, but we did not learn about circadian rhythms.
It sounds a little woo, but we are biological beings, just like plants and animals. When I learned how sunlight outdoors helps regulate my biology, and I started practicing it, that is when my sleep changed.
This show is for midlife women whose sleep has quietly fallen apart. If you wake at three in the morning, or you feel wired and tired, you are in the right place. I’m not saying you should never take a supplement or a pill if it works for you. I want you to work on the foundation, so whatever you add works better.
Ancient rhythms, modern mechanism
I want to be careful about something, because I care more about being accurate than being dramatic.
The people who built these traditions were not writing sleep advice. They were expressing devotion, meaning, and gratitude. I have no way to verify whether they understood circadian biology, and saying so would be an overreach. You deserve better than that.
What I will say is this. Many of the rhythms these traditions built into daily and yearly life happen to line up with what circadian science now tells us matters.
Ancient rhythms. Modern mechanism. I think that’s worth noticing.
Dawn, midday, and dusk
Look at the shape of a day in many traditions. In Islam, the first prayer of the day, Fajr, is at dawn. In Hindu practice, the daily devotions called sandhya are traditionally tied to dawn, midday, and dusk. In Judaism, Shabbat begins with candles lit shortly before sunset. In many Christian traditions, evening prayer, vespers, marks the day turning toward night.
Dawn. Midday. Dusk. The hours when light is changing the most are the hours many religions built their core practices around.
Whether or not you share any of these faiths, notice what the rhythm asks of the body. Be up as the light comes up. Pause as it fades. Bring in a candle or a lamp as the day closes.
That is, more or less, a morning light routine and an evening wind-down, built into the calendar long before anyone had a name for melatonin.
It isn’t only the day. It’s the year.
Think about how many celebrations sit near the sun’s turning points. The winter solstice, the shortest day of the year, shows up in Dongzhi in China, in Yalda, the longest night, in Iran, and in Yule in Northern Europe. The Inca held Inti Raymi, a festival of the sun, around their winter solstice. The spring equinox is Nowruz, the Persian new year. Midsummer brings bonfires and festivals across Northern Europe.
Some of the oldest structures we have were built around the sun. At Newgrange in Ireland, a passage tomb older than the pyramids, a beam of light reaches the inner chamber at sunrise around the winter solstice. Stonehenge is aligned to the midsummer sunrise and the midwinter sunset.
Not every holiday was created for the solstice, and scholars debate the origins of some of them. These are celebrations from all over the world and across history. But it is fair to say that many cluster around the sun’s turning points. People have been marking the changing light for a very long time.
Your eyes: the master clock
Now the biology. You don’t become a nurse if you don’t like biology. It was one of my favorite subjects, so I am going to take my time with it.
Most of us learned that the eye is for seeing. Rods and cones give you sight, color, and detail. That is true. But around the turn of this century, researchers described something that changed how we understand light. There is another kind of light-sensing cell in the retina, and it isn’t there to help you see a picture at all.
These cells contain a pigment called melanopsin. Their job is to measure how much light is in your environment, and they respond most strongly to the bright, blue-rich light of a daytime sky. (If you are a paid subscriber, the ebook includes a diagram of these cells and their full name.)
They send that information to a tiny area deep in the brain called the suprachiasmatic nucleus, or the SCN. This is your master clock.
The SCN doesn’t only keep time. It conducts. Think of an orchestra. Your liver, your gut, your muscles, and your skin all have their own clocks. In fact, most cells in your body have one. The SCN is the conductor that keeps them playing together. It tells your body when to feel alert, when your temperature should drop, and when to release melatonin and cortisol.
Here is what makes light so important. Left on its own, the human clock doesn’t run exactly twenty-four hours. For most people it runs slightly longer. Light is the daily reset. It’s how the conductor stays in time with the sun.
That is why morning light is the anchor. It tells the clock when your day began, and that helps determine when your night begins.
Your body also seems to keep track of how long the night is. In one classic lab study, when people were given longer nights, their bodies released melatonin for a longer stretch. Studies of real-world seasons are less consistent, and modern indoor lighting probably blurs the signal. Look at how many people struggle with sleep today.
But here is the bigger idea. Your body is always collecting data and information from the light around it, whether it’s natural or artificial.
Your skin: light sensors too
Your eyes are not the only place your body collects light signals.
Researchers have found light-sensitive proteins called opsins in human skin cells. Melanopsin has been reported there too, in at least one study, though another study did not detect it. So that part of the science is still being worked out.
I want to be clear about this word, because I know how it sounds. It is melanopsin, not melanoma. Melanoma is skin cancer. Melanopsin is a light-sensing pigment. They sound alike because they share the Greek word for dark. Melanopsin got its name because it was first discovered in the pigment cells of frog skin.
Your skin is more than a covering. It responds to light. The best-known example is vitamin D, which your skin makes when it is exposed to UVB light from the sun. Skin cells also have their own internal clocks, and researchers are studying how light influences them.
What those light-sensitive proteins in your skin actually do, and whether they influence your master clock, is still being worked out. The pathway we understand best, the one that sets your master clock, runs through the eyes. So I am not telling you your skin sets your circadian rhythm.
What I will say is that your body collects information from light through more than one route. When you step outside without sunglasses, with your eyes open and some skin exposed, you give it the fullest signal.
Because I’m a nurse, I have to say this too: practice safe sun. There are apps that help you measure your sun exposure and tell you when to go inside. There are natural sunscreens. If you use a traditional sunscreen, follow what you and your doctor have decided, or what you feel is best for you and your family.
Cortisol and melatonin: the dance
Now the part I’m excited about. It seems like you can’t open Instagram or Facebook without someone talking about cortisol and how to lower it. What nobody talks about is the relationship between cortisol and melatonin.
When we think of cortisol, we think of fight or flight. It’s our stress hormone, the one that helps us get away from the tiger. But cortisol also wakes us up in the morning. It’s our body’s way of saying it’s time to get going. Cortisol rises, blood pressure rises, and everything comes back on board.
Cortisol and melatonin have a rhythm, a kind of dance. Cortisol is higher in the morning, which is what wakes us up, and lower in the evening, when melatonin comes on board. Melatonin is our darkness hormone. It’s made when it gets dark.
But we live in a world where the daytime never ends. Bright, blue LED light at night suppresses melatonin, and cortisol gets out of balance.
I want to say something about melatonin, because it matters. Melatonin is not a sedative. It is a timing signal. It tells your body it’s biological night. That is very different from a medication that makes you sleepy. You’ve heard my story, so you know I’ve taken my share of melatonin.
When you allow darkness into your evening, by turning lights off, wearing blue-blocking glasses, lighting a candle instead of flipping a switch, or swapping your light bulbs, you are helping your body make its own melatonin. That’s why light is such a powerful lever when it comes to sleep.
What modern life did to the signal
When the signal is out of balance, there are usually two parts to it. The first is being inside during the day.
Typical indoor light measures in the hundreds of lux. An overcast day outside can be in the thousands. I have a lux meter on my phone. On a bright, sunny day I measured about thirty-five thousand. Back inside, I get five or six hundred. Most of us stay inside, so we get a blended, muddy signal when we should be getting that strong outdoor one.
The second part is the evening. We come home, get supper on, brush our teeth, and switch on every light. I keep candles in my bathroom. If I take a shower at night, I light a candle. If I’m brushing my teeth, I light a candle. Most people turn on the bathroom light and don’t wear blue-blocking glasses, and the instant you do that, you tell your body it is noon. Those light-sensing cells respond to blue light, and modern LED bulbs emit plenty of it. So your brain stops making melatonin and calls for more cortisol so you can face the day.
Then, because you didn’t make that melatonin, you feel groggy and slow in the morning, and wired and tired at night. The cycle continues because cortisol and melatonin are out of sync.
I want to add a caveat so you get the full picture. Cortisol is influenced by more than light. Stress, food, medication, and hormonal changes all affect it. But light is one of the most important levers, and it is one that not many of us are pulling. We look for a supplement, or a lot of other things, to manage cortisol, without trying to rebalance the cortisol and melatonin cycle that runs on a twenty-four-hour clock.
This is my opinion, but I have often wondered: do we really have a cortisol problem in this world, or do we have a lack-of-melatonin problem?
It isn’t only sleep
Cortisol and melatonin are not the only hormones on this schedule. Many hormones follow a daily rhythm that the master clock helps set. So when you go outside in the morning and get sunrise in your eyes, you reset the clock, and your body has a better idea of when to release the hormones it needs for the day.
Growth hormone, which supports repair and recovery, is released mostly during sleep. Deep sleep happens mostly in the first part of the night. Thyroid-stimulating hormone follows the master clock. So do leptin and ghrelin, the hormones tied to fullness and hunger.
When the clock signal is muddy, because we live indoors and then turn the lights on at night, I call it clock chaos. Think about jet lag. You cross time zones, and you are supposed to function on local time while your body is still on home time. That messes with you a little, or a lot. Now imagine it happening day after day, year after year, because we aren’t giving our body the right signals through light. That is what a lot of women are struggling with, and they don’t even know it.
Estrogen and progesterone are different. They run on a monthly rhythm, not a daily one, and light is not a substitute for what is changing there. But the daily rhythms around them are ones you can influence.
The same clock also influences how alert you feel during the day and how you feel in general. Light therapy is a recognized treatment for seasonal depression, which tells us how powerfully light can affect mood. For many women in midlife, energy and mood can already feel harder to manage. I’m not saying light fixes everything. But a good night of sleep really helps, and light is one of the levers that is usually missing from the conversation.
Everyone says, “Go outside and get morning light.” Nobody tells you why. It’s like telling your kid to do something. What’s the first thing they say? Why? I hope you are getting the why from this: light sets your clock, and your clock helps regulate what goes on in your body. When those things are working, we feel better, we sleep at night, and our bodies can repair.
Sleep matters for the brain too. In a small NIH study of twenty healthy adults, one night without sleep raised levels of beta-amyloid, a protein linked to Alzheimer’s disease, by about five percent in certain brain regions. The researchers were clear that this does not mean one bad night causes Alzheimer’s. But it fits the idea that sleep helps the brain clear waste products, and a lot goes on at night when we keep our twenty-four-hour clock in sync.
If you would like more on how sleep affects your hormones, I wrote about it in [link to “How Sleep Keeps You Young”].
Why light matters even more in midlife
I built The Sleep Nurse for midlife women because I am one. I am about to turn fifty-four, and I understand the struggle. I am grateful I discovered light five years ago, because it changed my life.
Yes, our bodies are changing. But here is the one thing I want you to understand: you have control over your light environment. You can go outside in the morning and get light in your eyes to reset your clock. You can decide which lights are on or off at night. You can decide whether to scroll on a phone that beams blue light at your eyes, whether to watch TV late, and whether to practice a wind-down routine.
These things are simple, and the simplest things are sometimes the hardest to put into practice. We are also told what to do without being told why. I believe that when we understand our bodies and trust our intuition, we have the power to change. That is what I want to do here: empower you.
Light and your blood sugar
Life is busy. You get home from kids’ sports and you are lucky to eat. Sometimes we eat late, or go out with friends. My best night is at home with my family, a book or a show, and an early bedtime, but I eat late sometimes too. We are told not to eat close to bedtime, and nobody explains why.
Here is something to pique your curiosity. Our bodies are less glucose tolerant at night than during the day, so the same meal eaten at night produces a different insulin and glucose response than the same meal earlier in the day.
In one small study, seventeen healthy adults ate the same standard evening meal on two occasions, once in dim light and once in bright light. The only difference was the light. After the bright-light meal, their glucose and insulin were higher, and their melatonin was lower.
In another small study, one night of sleeping with moderate room light on raised heart rate during sleep and left people more insulin resistant the next morning.
These were small studies in healthy adults, so I don’t want to overstate them. I have also seen people wearing continuous glucose monitors report changes in their blood sugar at night from blue light, apart from food or exercise. That is anecdotal. Maybe I’ll wear a monitor myself and let you know how it goes. Either way, it tells me light shapes how our bodies handle sugar, and it is something to think about.
The gap
Back to the gap I mentioned at the beginning. Most of our medical practice leaves out a huge piece of biology, and it is one that is in your control.
I have been that woman at the doctor who can’t sleep. What advice was I given? I wasn’t given advice. I was given a prescription for Ambien. In fact, I went in asking for it, because I desperately needed sleep so I could take care of people in the middle of the night. I still did not feel rested.
If you go to a functional medicine practitioner, they will often lead with supplements: melatonin, vitamins, and minerals to support your body and help bring down your cortisol. Those aren’t bad. But nobody talks about your light routine. Simple changes in your daily habits can help your body make its own melatonin, and you may not need a supplement. I have always believed that intrinsic melatonin trumps a pill any day. I have experienced that in my own life.
As a nurse, I am often the first person a patient talks to, and we do a nursing assessment. I have asked people about some of the most private parts of their lives. But I have never once asked, “How is your light environment? Did you get outside and see sunrise today? Are you spending too much time in artificial light?” Those were never part of any assessment I was taught.
The great thing about light is that it is free and low risk, and it works upstream of almost everything else, because it sets the clock that sleep depends on.
Genesis started with light. I think there is something to that. Not because it is ancient, but because when you begin with the signal that sets the clock, everything downstream has a better chance.
Try this tomorrow
Morning: get outside within the first hour after you wake, for a few minutes, without sunglasses if you can. Never look directly at the sun.
Midday: get some daylight, even for a few minutes.
Evening: when the sun goes down, let your home follow it. Dim the lights, and use lamps, candles, or warm bulbs.
If that feels like a lot, start with the first one and see how it feels. If you have an eye concern, or take a medication that makes you sensitive to light, check with your provider first.
Waiting right outside your front door
Long before we had a name for melatonin, people organized their days and their years around light. We can do that too. There is nothing to buy and nothing to prescribe. It is waiting for you every morning, right outside your front door.
Thank you for spending some time with me. This is the first of many episodes of The Sleep Nurse. If you found it helpful, I hope you will follow the show and subscribe to my Substack, and come along on this journey into better health. I truly believe sleep is the foundation of our health, and it begins at sunrise.
Each week I am going deeper into my five sleep macros. This episode combined the first two. I will keep going into why we need light and why we need sleep, and why it is worth adjusting our daily routines to support that internal master clock. When that clock is in sync, it supports our hormones, helps bring cortisol and melatonin back into balance, and we tend to feel happier, have more energy, feel more rested, and have more patience with our families.
Align your day. Restore your night.
This post reflects an educational, general-audience summary of sleep science. It is not a substitute for individualized medical advice.
References
Albreiki, M. S., Middleton, B., & Hampton, S. M. “A single night light exposure acutely alters hormonal and metabolic responses in healthy participants.” Endocrine Connections, 2017;6(2):100-110. doi:10.1530/EC-16-0097
Berson, D. M., Dunn, F. A., & Takao, M. “Phototransduction by retinal ganglion cells that set the circadian clock.” Science, 2002;295(5557):1070-1073. doi:10.1126/science.1067262
Blume, C., Garbazza, C., & Spitschan, M. “Effects of light on human circadian rhythms, sleep and mood.” Somnologie, 2019;23(3):147-156. doi:10.1007/s11818-019-00215-x
Czeisler, C. A., Duffy, J. F., Shanahan, T. L., et al. “Stability, precision, and near-24-hour period of the human circadian pacemaker.” Science, 1999;284(5423):2177-2181. doi:10.1126/science.284.5423.2177
Gooley, J. J., Chamberlain, K., Smith, K. A., et al. “Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans.” Journal of Clinical Endocrinology & Metabolism, 2011;96(3):E463-E472. doi:10.1210/jc.2010-2098
Haltaufderhyde, K., et al. “Opsin expression in human epidermal skin.” Photochemistry and Photobiology, 2015. PMID: 25267311
Hattar, S., Liao, H.-W., Takao, M., Berson, D. M., & Yau, K.-W. “Melanopsin-containing retinal ganglion cells: architecture, projections, and intrinsic photosensitivity.” Science, 2002;295(5557):1065-1070. doi:10.1126/science.1069609
Kusumoto, J., et al. “OPN4 belongs to the photosensitive system of the human skin.” Genes to Cells, 2020. doi:10.1111/gtc.12751
Mason, I. C., Grimaldi, D., Reid, K. J., et al. “Light exposure during sleep impairs cardiometabolic function.” Proceedings of the National Academy of Sciences, 2022;119(12):e2113290119. doi:10.1073/pnas.2113290119
Morris, C. J., Yang, J. N., Garcia, J. I., et al. “Endogenous circadian system and circadian misalignment impact glucose tolerance via separate mechanisms in humans.” Proceedings of the National Academy of Sciences, 2015;112(17):E2225-E2234. doi:10.1073/pnas.1418955112
Provencio, I., Jiang, G., De Grip, W. J., Hayes, W. P., & Rollag, M. D. “Melanopsin: An opsin in melanophores, brain, and eye.” Proceedings of the National Academy of Sciences, 1998;95(1):340-345. doi:10.1073/pnas.95.1.340
Sandu, C., Dumas, M., Malan, A., et al. “Human skin keratinocytes, melanocytes, and fibroblasts contain distinct circadian clock machineries.” Cellular and Molecular Life Sciences, 2012;69(19):3329-3339. doi:10.1007/s00018-012-1026-1
Shokri-Kojori, E., Wang, G.-J., Wiers, C. E., et al. “Beta-amyloid accumulation in the human brain after one night of sleep deprivation.” Proceedings of the National Academy of Sciences, 2018;115(17):4483-4488.
Wehr, T. A. “The durations of human melatonin secretion and sleep respond to changes in daylength (photoperiod).” Journal of Clinical Endocrinology & Metabolism, 1991;73(6):1276-1280. doi:10.1210/jcem-73-6-1276
