In this presentation Dr. Deanna Minich explains how modern indoor lighting and artificial blue light have dramatically altered human light exposure, creating a "darkness deficiency" that disrupts the body's circadian system. She contrasts natural daylight (10,000–100,000 lux) with typical indoor daytime lighting (≈100 lux) and nighttime lighting (≈1,000 times brighter than natural night). The talk links this mismatch to endocrine disruption, highlighting melatonin’s central role alongside vitamin D. Minich details melatonin’s biosynthesis, its systemic functions beyond sleep (immune modulation, mitochondrial health, glymphatic clearance), and its circadian rhythm peaking at 2–4 am. She describes health consequences of chronic light pollution—metabolic disease, cardiovascular disease, mental health disorders, cancer (especially in shift workers), and neurodegeneration—emphasizing that even a single night of 100 lux exposure can impair heart‑rate variability and increase insulin resistance. Individual susceptibility factors (light‑colored eyes, children, age‑related melatonin decline) are discussed. Finally, she offers actionable mitigation strategies: bright morning light exposure, reducing evening blue light, aligning meals and activity with natural zeitgebers, and, when appropriate, supplemental melatonin, framing these changes as both personal and planetary interventions.
Chapters
Seeing the dark sky affects our health in a number of different ways. So where we have been, where we are now, in terms of historical exposure to light, if you even have an app on your phone that can measure lux, which is the unit of light, you can clearly see that if you go outside on a bright day, that we're going to see something on the average of 10,000 to 100,000 lux. However, now since we're indoors, we are not getting quite that same same exposure. And similarly, as Dan was talking about at night, you know, we're supposed to have darkness, but now we have just the reverse where we have now more artificial blue light indoors. And that's coming from things like tablets, smartphones, computers, light bulbs, and even urban area emitted light. So essentially we're going against our natural rhythm. It is quite ironic that as you can see from the quote here, most of our time is currently spent indoors under light levels during the day that are typically 100 times dimmer than natural daylight and about 1,000 times brighter than natural light intensities at night. So we have flip flopped our natural rhythm and that has repercussions on our human health. So, yeah, the planet, just like Dan said, everything is interconnected. So this is impacting our physiology. We're starting to see more metabolic diseases, cardiovascular disease, mental disorders. Cancer is a big one as it relates to light pollution since it's an endocrine disruptor. We especially see that with shift workers and increased rates of breast cancer. We obviously see impacts in sleep and other circadian rhythm disorders that would be locked into our endocrine system. This can impact our sense of immune health and even have complications during pregnancy and childbirth. So I'd like to pose a question to all of you here because during the pandemic we learned so much about vitamin D, we learned so much about sunlight and how important it was that we were out in the light to get that vitamin D. I would also propose, and I was one of the authors on a paper published in nutrients in September 2022 asking whether or not we actually have a darkness deficiency. And perhaps we need to be as vigilant about darkness as we are about sunlight. And if you compare vitamin D and melatonin side by side, what you actually see is a yin and yang type of interrelationship between both of them. Vitamin D levels are implicated in melatonin levels. Melatonin, I do want to talk about a bit more as to what it's doing in our bodies and why it's essential as it relates to darkness. Light Pollution, in my view, is one of the most societally accepted endocrine disruptors. We all know how bad plastic is. We. We all know how bad air pollution is. But light pollution just still needs to get onto the radar of many different people. The common person, you know, just through their daily, everyday lives, are being subject to a lot of this artificial light at night. Everything from children going to sporting events at night, workers under fluorescent lighting, using a smartphone in bed at night, waking up with that in the morning, exercising, doing all the things that we think are really good at night, but then having that exposure, exposure to light, and also evaluating our work life and what we do for a living, because much of that can also be implicated in light pollution. So what are the implications? When we start to alter our light and dark rhythms, we start to see circadian disruption. And I would say we don't have a circadian rhythm. We have a circadian system. It's a system of the body, just like the gastrointestinal system, the neurological system. And when we start to see changes in that circadian system, we start to change things like our eating, our sleeping, our activity. And this then translates into impaired metabolism, endocrine, metabolic, cardiovascular disease. So, again, my big takeaway here is I'm very interested in the endocrine system. The endocrine system gives us hormones. Those hormones determine our behavior to a large extent. And it's not just melatonin from the pineal gland that is disrupted. We also see changes in thyroid hormone, glucocorticoids, stress hormones, and even hormones that are involved with fertility. I just want to talk a little bit about melatonin and why it's relevant for this discussion. We know that melatonin is an ancient molecule that is found throughout the body. It's amphiphilic, meaning that it is in water and in fat tissue. So it traverses the entire body. As you can see, there pretty much is no body tissue. I would say that is is melatonin devoid. We have melatonin circulating at all times, and from an endocrine perspective, it's highest in darkness, meaning that from an endocrine hormonal, systemic impact, when the retinal ganglion photosensitive cells in the eye perceive darkness, and these cells are enriched in melanopsin. What we see is that there is this translation ultimately to the pineal gland in the brain to produce melatonin from tryptophan, then onto serotonin, then to melatonin. This then gets transmitted throughout the body and then ripples through the clock Genes at the level of every cell in the body. And as you can see here, from this diurnal production of melatonin through the course of a day, that essentially during the sunlight, during the daytime hours, we don't have melatonin in our blood or even circulating to a large degree, but it starts to rise as it becomes dim, and then we start to see a peak at that pinnacle of darkness between 2am and 4am so we actually need both day and night for healthy melatonin. So it's equally important to get bright light exposure first thing in the morning. So I live in the Seattle area, very cloudy, but it's even important for people in cloudy areas to be going outside and to expose the eyes, the retina, to that bright light in order to have that proper melatonin offset and then ultimately to increase nocturnal melatonin levels. So that bright light in the morning is important, just like the darkness at night. And we know that LED and other bulbs can suppress melatonin by over 50%. When we work by candlelight and fireplaces, this does not impact our melatonin levels. And the reason why we care about melatonin is not just because of sleep. I think that melatonin has been pigeonholed into just being thought of as a sleep hormone. It's actually much more than a sleep hormone from the pineal gland. It's produced within the cells by the mitochondria, and it has a role in the immune system, body temperature, hormone secretion, the gut microbiome, and most recently has been implicated in things like brain detoxification at night and working through the glymphatic fluid flux. If you just look at different health conditions and their rise, clearly we have a rise in brain and neurodegenerative type of disorders in the 21st century. Is that implicated as a result of light pollution? And even through melatonin, is that divining rod? Perhaps. We see a number of different diseases having some type of implication as it relates to melatonin. I want to also point out that there is a personalized approach to light pollution. So people with light colored eyes, like blue, green, even light brown, are going to be more more susceptible to those suppressive effects of blue light at night and having suppressed melatonin production compared to those who have dark colored eyes. That doesn't mean that people with dark colored eyes are exempt from any kind of effect of light pollution, but it's something to consider that there can be greater effects in certain individuals. The other group that is more vulnerable to light at night, pollution and melatonin suppression would be children. And I just think about all of those kids on all of those smartphones and devices late at night changing their melatonin. And you know, if you look over the course of one's lifespan, we have the most amount of melatonin as a child, pre puberty. Once a child starts to go through puberty, those levels come down and then we hit rock bottom in the mid-50s and onto the 6th, 7th, 8th and on decades that has been referred to as melatoninopause. And perhaps there's some, I would say a parallel risk there with chronic diseases like I was just speaking about with neurodegeneration, cardiometabolic and others. You know, the one that I think should concern us all is the increased rates of cancer and how light pollution can be changing things like inflammation in the body. And even one night of poor sleep the next day can lead to a ripple effect of many different endocrine, metabolic, even societal types of impacts that can in the end be very significant. There's a lot of research done on immune dysfunction and circadian rhythm and how an important factor it is to have that proper sleep, proper light exposure, and not be flip flopping our circadian rhythm, because then we can start to see increased inflammation, increased immune activity. So essentially every cell in the body, I would say there are some cells more than others, especially the liver, is prone to these changes at the level of the circadian rhythm and what gets sent out by melatonin at night. So when we start to change those rhythms again, if we have what is referred to as clock misalignment, we see that many different body systems become impacted. So how do we get back to nature? You know, that's really what I'm here to speak to, you know, the individual. Because if we can be making individual changes, we can be making the ecosystem changes, the planetary changes too. So what we want is more on the green side, more on the right here, having those proper zeitgebers or those time givers of eating. That's why we've had a lot of discussion in nutrition about fasting and time restricted feeding, reducing that artificial light, punctuating our day with physical activities. This gets us back in proper rhythm. So I just want to show you this too, because all of the hormones do have a circadian rhythm to them. So just because we're altering melatonin through circadian rhythm changes does not mean we're not impacting the others, like thyroid hormone, cortisol, testosterone, growth, growth hormone, even insulin. So I, I do think metabolism is something to be looking at because if we are changing insulin by way of artificial light exposure at night, then that has implications for blood sugar cortisol cardiovascular disease. And as you can see here, this is a pretty staggering study finding that even one night of 100 lux light, which is pretty significant during sleep, can alter nighttime heart rate, decrease heart rate variability and increase next morning insulin resistance. Now imagine that somebody is doing that every night and how that can ultimately pile up into increased risk for certain diseases. And as I mentioned, neurodegeneration is one that has a tethering to artificial light at night and also to disturbances in melatonin. So think about increased depression, increase anxiety, changes in cognition. I think we need to be thinking about light. And I want to leave you on a good note, obviously thinking about light exposure recommendations. So I have these here. You are going to get the slides so you can look at those later. But I want to leave you with, you know, what do you do about this? You know, that's why we're all here. And thanks to Rebecca for pulling us all together from different fields. I think as much as possible, we do need to get back to nature. We need to honor the darkness as much as the light. I don't know if you've seen it, but there are even darkness retreats now where people deliberately spend time in that darkness to recalibrate at a physical, emotional, mental, spiritual level. We really need to be mitigating our blue light exposure at night, having that early morning bright light and punctuating our day with food in a way that also helps us with circadian rhythm and if needed, bring in supplemental melatonin to help us to reduce inflammation, antioxidant balance, kind of getting that oxidative stress in alignment. So I'm going to stop there. I know this is really short. Just 10 minutes. This is the article that we published, so if you're interested, it's.
