CHAPTER TWO It Starts with Sleep

It Starts with Food. Or so I thought. I’ve presented over 150 seminars and written two books about food, including one with that very title. But as I relayed in the Introduction, my work on food really grew out of a broader perspective connected to the seasons and the earth, and entailing physiological, psychological, and emotional components. It was meant to provide a framework of scientifically sound principles, within which people could create their own more granular, nuanced versions of health and wellness. Food was an important starting point, but never the sole focus.

In fact, my approach to health and wellness has always been multifaceted. Early in my career, I practiced physical therapy for almost ten years, gradually expanding into strength and conditioning work, nutrition, and functional medicine. When I first encountered people like Kim, I began experimenting with different starting points to jump-start their lives. I sometimes began with strength training and cardiovascular conditioning, trying to improve overall health through better metabolic rates, muscle mass, and the like. I also tried stress management as a point of entry. But I rapidly figured out that food was the most practical and impactful starting point.

When we’re “stuck in summer,” our problems become muddled, confused, and sometimes a bit frustrating. Food can be a useful place to intervene because dietary changes can indeed rapidly improve a person’s quality of life. Other lifestyle changes are crucial to optimal wellness, but their effects are more difficult to perceive and oftentimes imperceptible. Looking back, however, I think I might have overemphasized food’s centrality, and underestimated that of sleep. As I coached clients and gave seminars, I saw that when people didn’t prioritize sleep, it didn’t matter how impressive their diets were—their health, overall, was subpar. Sleep certainly works in tandem with nutrition; dietary improvements can lead to significant, sometimes dramatic, improvements in sleep. But for our physical, emotional, mental, and social health, sleep is a key foundational element. In many cases, sleep eclipses food in importance. So, I hereby correct myself: optimal health really does start with sleep and the inherent rhythmicity that it is (or should be) built on.

Our National Sleep Recession

I remember being approached by a woman in her late twenties after a seminar a few years ago. Let’s call her Jill. She loved high-intensity interval training (HIIT) workouts, which involve short spurts of highly strenuous activity like sprinting, heavy lifting, or kettlebell routines. Research suggests that such workouts build lean muscle mass, increase metabolism, and are more efficient at improving fitness than working out at lower intensities for longer periods of time.¹ Jill’s enthusiasm for HIIT training was apparent—she did these strenuous workouts multiple times a day, six days a week. She was largely following a Whole30/Paleo diet, avoiding processed foods, artificial sugars, and grains, instead emphasizing healthy vegetables and complete protein sources. From her quick overview, however, it was clear to me that she was likely restricting her food intake too much.

Here’s what was baffling about Jill. At a superficial glance, she was a lean, muscular woman. Many of her friends and passersby on the street admired her body, and used words like “badass” and “hardcore” to describe her. “Wow, you are so lean and cut,” people would fawn, “you inspire me to get off my rear and work out more.” But appearances were deceiving. When you took a closer look at Jill, she came off as tired, in the manner of someone who’s just pulled an all-nighter. Powered by caffeine and sugar, and deprived of sleep, most people who’ve stayed up look a little rough and haggard. They have bags under their eyes and a subtle slump in their shoulders. Jill certainly looked that way. Her skin also bore many hallmarks of someone who engaged in excessive amounts of high-intensity exercise. It was graying a bit and becoming prematurely wrinkled. I’d seen this a lot in my endurance training clients. The chronic stress of such intense workouts leads to ongoing cortisol release throughout the system, causing structural breakdown in things like collagen that keep our face and skin looking youthful and healthy.

Like many competitive athletes I’d seen, Jill was prematurely aging herself. And not just superficially. Her hormones had become unbalanced and her menstrual cycle was irregular, which meant she had severe PMS symptoms that could have led to infertility. She also didn’t feel good on a day-to-day basis and relied on stimulants to power through those long afternoons at work. Hardly the picture of optimal health.

When I asked her about her sleep, she seemed baffled: “What has that got to do with anything?” To get to her morning workout, she was rising before sunrise. She then returned to the gym during some of her lunch breaks, when she could get away, or in the evening. By the time she had finished and driven home and fixed a meal, it was already bedtime. Or it should have been. Jill had trouble falling asleep, and for good reason. Her intense workouts ramped up cortisol levels, putting her into a fight-or-flight state. From an evolutionary standpoint, such a state of readiness, hypervigilance, and stimulation was a perfect response when we needed to fend off hostile predators on the savannah, to run or fight for our lives. But it certainly isn’t optimal for a body preparing for sleep, and it prevented Jill from sleeping as much or as well as she might have.

Even when confronted with these facts, Jill didn’t want to talk about her sleep or caffeine consumption. She wanted to know how much lower she should take her carbohydrate intake because she was struggling to move some stubborn belly fat. This is again something I’d noticed among distance runners and triathletes (and other recreational athletes): their arms and legs are muscular, sinewy, and fairly lean. But if you look closely, they often have a little pouch around their middle, a classic hallmark of excess cortisol release over long periods of time. Jill was sure she needed a dietary fix because at ten to twelve workouts per week, she simply couldn’t fit in any more training. Following her evening high-intensity training, she would often need a couple of hours to unwind, which she would spend under bright lights at home, either watching TV, surfing the web on her laptop, messaging friends on her phone, or, more typically, all the above in turn.

She was layering stimulation on top of stimulation—news of her friends, the dopamine surges from smartphone notifications, the melatonin-reducing blue light from the Netflix show she streamed on her tablet. She would, eventually, drag herself off to bed, or fall asleep among her humming devices, collapsing more from sheer exhaustion than restful repose. Feeling tired but wired, it would generally be some time around midnight before she was falling into what she described as a relatively light sleep, with her alarm set for 5:00 a.m., ready to start it all over again.

I wish I could say this was a rare and extreme example. But such stories are more common than you might think. The exact details vary—sometimes the story doesn’t involve getting up so early for exercise, but for a daily commute. Still, the overarching pattern is generally the same. Modern civilization is suffering through a massive sleep recession, with the CDC reporting that over one-third of US citizens get less sleep than the recommended seven hours each night.² In the early twentieth century, this wasn’t the case. Americans logged around nine hours.³ But along came artificial light, revolutionizing our economies and our sleep routines. Following the introduction and eventual ubiquity of the light bulb in the twentieth century and the rise of individual LCD screens throughout the twenty-first, our sleep has steadily declined.⁴ Now, we get up early and stay up late in a world that stays lit 24/7. The ethos of the city that never sleeps has spread to the entire modern world.

Many of us offer up similar reasons for burning the LEDs at both ends of the day. There are not enough hours in the day to do all the things we want or need to do. There’s the daily commute, becoming ever greater as we choose to live farther away from our workplaces or are forced to for economic reasons, such as affordability of housing. Early in the morning or late at night might be the only space we get for me time, away from work or our often overstimulated kids. Our days and our time are so overscheduled that the moment anything extra falls in our lap, we need to borrow (read: steal) time from sleep. We routinely treat our sleep like a credit card in that we feel like we have money to spend, but in reality are barely keeping up the minimum payments.

Is it really that bad, though? After all, recent evidence challenges the notion that our preindustrial ancestral cousins slept more than we postmodern humans do, and that we should be sleeping from sundown to sunup because that’s how Paleo man slept. UCLA researchers followed the sleep habits of three contemporary nonindustrial societies.⁵ Studying the few remaining societies that live without access to electric light, they reasoned, may illuminate current sleep trends. Absent artificial light and digital technologies, do we sleep longer and better?

At first blush, the research appeared to indicate that these populations spent much more time sleeping than most people living in modern society—seven to eight and a half hours each night. However, further analysis of the data collected revealed that of this time in bed, only five and a half to seven hours was actually spent asleep. This is roughly comparable to modern postindustrial societies.⁶

This research generated many commentaries and interpretations, the most obvious being that we can all relax—that midnight to 5:30 a.m. sleep routine you have is in fact perfectly normal. “The argument has always been that modern life has reduced our sleep time below the amount our ancestors got, but our data indicates that this is a myth,” said Jerome Siegel, leader of the research team and professor of psychiatry at UCLA’s Semel Institute of Neuroscience and Human Behavior.⁷ “I feel a lot less insecure about my own sleep habits after having found the trends we see here,” echoed lead author Gandhi Yetish, a PhD candidate at the University of New Mexico.⁸

I can’t quite embrace that conclusion. The sleep patterns of these tribes seem to work well for them, but based on my work with hundreds of consulting clients, that same amount of sleep doesn’t seem to support healthy outcomes in different, more stressful environments. We industrialized humans burn the metaphorical candle at both ends … with a blowtorch. In the same way that doing a lot of intense exercise requires more nutritious food for full recovery, living a modern life of stress and overstimulation might require more sleep than if we were living like our electricity-free counterparts. Sleep of closer to eight or nine hours might be required if we’re perpetually dealing with the sum total of financial stress, environmental toxins, inflammatory processed foods, social pressure to look a certain way or to acquire more material belongings, and chronic exposure to junk light (reducing the quality of our restoration during time spent in relative darkness, whether we’re asleep or not).

Hello, Darkness, My Old Friend—and Hello, Light

One of the many major differences between the preindustrial societies the UCLA team studied and the sleeping habits of humans in modern societies is less about time in bed and more about the level and duration of darkness we experience before sleep.⁹ To initiate the high-quality, restorative sleep we all seem to be craving, darkness is crucial. But darkness is something many of us only get once we are in bed and attempting to fall asleep. Even then, given the prevalence of bright alarm clocks, LED lights from the various devices in our bedrooms, light pollution from external sources such as streetlights and vehicles, not to mention both the light and sounds emanating from phone notifications coming in at all hours of the night (“but my phone is my alarm clock”), our supposedly dark bedrooms are anything but.

While many health experts rightly emphasize the importance of sleep, very few explicitly mention the biological importance of spending time in darkness before we get into bed. One exception is Richard G. “Bugs” Stevens, professor of medicine at the University of Connecticut, who was surprised that time spent in darkness wasn’t a factor in the UCLA sleep study: “… a crucial aspect of the study’s findings has not been discussed in news stories or the paper itself,” he observed in the Washington Post. “People in preindustrial societies spend much more time in darkness than people in the industrialized world.”¹⁰ Yet it is becoming increasingly evident to specialists like Bugs that humans have a daytime physiology, triggered by bright natural light exposure, and a nighttime physiology, triggered by the absence of light and exposure to darkness.¹¹ In our daytime state we are (or should be) alert, active, productive, and hungry, driven by key daytime hormones and neurotransmitters such as cortisol, dopamine, and serotonin. After sunset, we transition to our nighttime physiology—our body temperature begins to fall, our metabolism slows, and our readiness and drive for sleep increases as the sleep hormone melatonin surges through our bodies. Except, as we saw in the last chapter, it isn’t a sleep hormone, per se. It’s a darkness hormone.

Come on, admit it. You sidle up to your laptop and watch This Is Us or random YouTube videos for an hour, bathing your eyes in artificial light. But then you get dozy, and finally turn off your television, smartphone, or computer, hoping that slumber quickly follows. Except it doesn’t always, does it? That’s because our daily rhythms are just like the seasonal ones—they require transitional periods. Our bodies are not like light bulbs that are either on or off. Every night, our bodies need to shift from one physiological state (daytime) to the other (nighttime). Absent this gradual transition, we remain restless, becoming progressively more anxious—often to the point that we can’t fall asleep. And when we can’t sleep, we indulge in still more screen time or we indulge in nighttime snacks, getting up to watch TV, have a bowl of ice cream, or scroll on our phone. Or we turn to sleep aids, from mechanical to herbal to pharmaceutical. In 2015 Americans spent $41 billion on white-noise machines, sleep-inducing mattresses, sleep coaches, sleep gadgets and smartphone apps, and other such paraphernalia. By 2020 a BBC Research analyst predicts that number will swell to $52 billion.¹²

So, what’s the answer? Should we just turn out the lights after sunset and assume that we’ve solved our sleep-related maladies? I wish it were all that easy. First, if you think asking people to give up a favorite food and change their diet is hard, try prying their smartphones and tablets from their hands. Second, and most pertinent, the dark needs to be balanced with the light. Our nighttime physiology is inextricably linked to our daytime physiology, which itself is highly dependent on our exposures to sufficient bright light, particularly in the early morning.

And therein lies the rub. We’re getting too much light at night, and we’re also not getting enough bright light during the day. For many of us, perhaps most of us, our days and nights have become inverted. We are living in dark days and bright nights. I’m not just talking about night-shift workers here, though clearly this is the most extreme example. A significant portion of the population in our modern developed societies work indoors, where exposure to natural light is scarce. This includes retail workers deep inside multilevel shopping malls, office workers without a window seat, factory workers operating inside windowless buildings, medical staff working in hospitals, and air traffic controllers in blacked-out radar rooms. I recently observed that a local bicycle store permanently blacked out their windows (the only source of natural light) just to fractionally increase the shelving space inside by a few square feet. In addition, with the continual rise of urbanism and large sprawling cities where few can afford to live close to where they work, many people must leave home before sunrise and return home after sunset, for much of the year.

But it gets worse. Look around on a bright, sunny morning and you’ll often see a significant number of people wearing sunglasses. You’ll even see this on the not-so-sunny mornings, or in the subway. In heavily built-up cities, such as New York, the surrounding buildings can block much of the available sunlight and cast significant shadows. But you will still see people wearing sunglasses, blocking the light further still. In stark contrast to our preindustrial human ancestors, who would have awoken slightly before sunrise and who would have spent their mornings actively exposed to bright natural light (sans Ray-Bans), we modern humans might be lucky to get thirty to ninety minutes of bright light exposure during summer mornings, often filtered by sunglasses and/or UV-tinted windshields, before we scurry back indoors, missing out on not only the peak brightness of the day, but also a significant duration of bright light exposure.

To understand our (lack of) light exposure further, we need to understand a couple of measurements: lumen and lux. Lumen is a measurement of light intensity (brightness) taken at the source of the light itself. As light travels away from its source, it scatters into the surrounding area and its intensity changes. Think about a bright LED flashlight shining directly into your eyes versus being fifty feet from it. Lux takes the lumens of a light source and factors in the area over which the light spreads, giving an indication of how bright, for example, a light source is in a particular room.

To give you some scale and perspective on lux readings, the light on a clear day in the summer can exceed 100,000 lux; on a dark and cloudy day in the same outdoor space, it can be as low as 1,000 lux. Full daylight but indirect sunlight can measure 10,000 lux. At night, with a full moon, it would be less than 1 lux. Sunrise or sunset on a clear day is around 400 lux. Now let’s compare these natural light scenarios to some typical artificial lighting. Bright office lighting comes in around 300 to 500 lux (comparable to sunset). An office hallway might be around 100 lux. A very brightly lit home living space might come in at a similar reading to the office but is more likely to be under 100 lux. That means that bright natural daylight is one hundred to one thousand times brighter than our typical indoor lighting. That’s a huge difference.¹³

Linda Geddes, author of the book Chasing the Sun: The Astonishing Science of Sunlight and How to Survive in a 24/7 World, set about on an interesting light experiment in conjunction with sleep researchers from the University of Surrey (UK). Following the same argument that I make here, that our preindustrial ancestors lived and slept in tune with the light and dark cycles of the natural world, Geddes set about to live for four weeks with as little exposure to artificial light after sunset as practicably possible (in the context of having a career and family to manage). Part of her experiment involved measuring the intensity of her light exposure during the day.¹⁴

On one particular morning, sitting in the park after dropping her children off at school, Geddes measured the light intensity at 73,000 lux. She took another reading at her desk once she arrived in her office, 120 lux. That is, the light in the environment she would be exposed to for much of the day was about one-fifth of the light intensity she might get immediately after sunset, and only a tinier fraction of what she would get if she were outside. Even moving to a desk closer to a window where it was sunnier, the light intensity was 720 lux—still over one hundred times less than her light exposure in the park earlier that morning.

Across the duration of Geddes’s four-week experiment, where she attempted to get more light exposure during the day, her average exposure between 7:30 a.m. and 6:00 p.m. was just under 400 lux in the first week of the experiment and as low as 180 lux in the second (but these were still increases from her preexperiment baseline of 128 lux). The experiment did take place in the middle of a UK winter when sunset occurred at 4:00 p.m. Nonetheless, the magnitude of the difference in light intensity between indoors and out is clear, being in the order of at least one hundred times less for the indoor environments, irrespective of the season.

Inspired by Geddes’s experiment, I purchased a light meter from an electronics shop and began tracking the brightness of the light in the various settings I would find myself in on a daily basis. Without exception, and irrespective of the weather or cloud cover, outdoor light was always at least ten times brighter than the indoors, and more often one hundred times brighter. Early in the morning, the light in my house might be 100 lux, while outside at the same time, in indirect light, it was 1,000 lux. At my local café, it would be 300 to 400 lux seated indoors, and 30,000 to 40,000 lux seated outdoors. Conversely, at night, I recorded outdoor readings of less than 1 lux, while indoors, with the bright, blue-light-emitting artificial lights on, I would get around 200 lux. Switching the main lights off and using a low-wattage incandescent lamp brought the brightness down to under 10 lux.

As these experiments demonstrate, we’re not getting the bright light we need during the day. As a result, we’re confining ourselves to chronic summer sleep. We are in effect living in the weak winter light of the high latitudes during the day. Our indoor lives send the message to the light-sensitive part of our brains that it’s dawn or dusk most of the time. With our increasing bright artificial (blue) light exposure after sundown, quite literally at the push of a button and flick of a switch, we switch to high-latitude summer light in our evenings. No wonder our brains don’t know whether to be alert or asleep a lot of the time! We’re sending really inconsistent and incoherent light signals. In the following chapters, we’ll discuss how we’re in perpetual summer mode when it comes to our diet, physical movements, and social interactions. Playing out summer sleep patterns throughout the entire year is just as unnatural and damaging to our health. Returning to the natural oscillation of the light/dark cycle on both a daily and seasonal basis is a vital and often overlooked route to better health and wellness.

It’s All About the Neurology, Baby

How exactly does insufficient exposure on a regular basis to bright light or darkness disrupt our bodies’ physiology? Let’s take a closer look at the basics of our light biology and the circadian and diurnal rhythms mentioned earlier in the book. Natural daylight—light from the sun—contains the full spectrum of light, including invisible ultraviolet light at one end (which is involved with vitamin D production in the skin, tanning, and, when overexposed, sunburn) and invisible infrared light at the other (which gives us the sensation of warmth and heat). It is a specific segment of this spectrum—the shorter wavelength blue-light spectrum—that is involved in signaling and synchronizing our sleep-wake cycles. The presence of blue light stimulates our transition to daytime physiology and wakefulness; its absence, the transition to nighttime physiology and sleep. It is this diurnal light-dark cycle that sets the endogenous circadian rhythm described in chapter 1.

Receptors in our eyes (called intrinsically photosensitive retinal ganglion cells, or ipRGCs) that make up part of our circadian rhythm system contain a vitamin-A-derived protein pigment, melanopsin, that is sensitive to intense blue wavelength light, the kind we get from sunlight not long after sunrise.¹⁵ When morning light stimulates these receptors, it activates neural pathways and hormonal responses that help increase our wakefulness, alertness, and body temperature. The light literally wakes up and primes our body for the day. That light also suppresses melatonin. As the intensity of blue light declines toward the end of the day, being replaced, at first, by visible red light (such as is seen at sunset, or emitted by firelight), and eventually full darkness, melatonin secretion increases, initiating our sleep processes and helping us to, hopefully, fall asleep. A key part of our brain, the suprachiasmatic nucleus (SCN), or the master body clock, coordinates and synchronizes these light- and dark-triggered circadian rhythm events day after day. We are exquisitely tuned to the presence or absence of light, and we have very specific physiological responses to differing light triggers.

When it comes to sleep, many people focus on melatonin as our primary “sleep hormone” because of the association of low levels of melatonin and poor sleep architecture (the cyclical pattern during our sleeping hours). When you lie awake at night, or have restless sleep, low melatonin is usually a big part of that. This often leads us to hit up the local drugstore or Amazon.com in search of melatonin supplements, which we use as either an everyday sleep aid or to stave off jet lag when traveling. Melatonin, however, is most potent when produced as a downstream product of our daytime physiology, specifically, its precursor, serotonin.

The neurotransmitter serotonin, which I’ve described as characterizing the fall season, is important to us every day. It helps regulate our mood, appetite, memory and learning, and, you guessed it, sleep. Exposure to bright early morning natural light boosts serotonin production (in conjunction with the amino acid tryptophan and other vitamins and minerals consumed as part of a protein-rich breakfast), providing the raw materials for the melatonin required for our nighttime physiology.¹⁶ The converse is also true. The low melatonin leads to poor sleep train of thought is an oversimplification. In fact, low morning light exposure plus a low protein intake (leading to low tryptophan and cofactor intake) leads to low serotonin production, which leads to low melatonin production, which leads to poor sleep. If we don’t supply the building blocks and bright daytime light triggers for serotonin synthesis, we won’t have adequate serotonin to convert into melatonin. You know that pleasantly relaxed, tired-but-not-frazzled feeling you have after a long day of hiking or playing at the beach? And you know how you often naturally want to head to bed fairly early on those days, maybe after sitting around a bonfire with your friends or family, and how you usually sleep really well that night? Yeah, that’s the effect of lots of bright daytime light, lots of serotonin production, and lots of melatonin availability. That’s the normal experience of the effect of natural light on your physiology. At the same time, we all now know that nighttime, blue-light screen time suppresses melatonin, so we could still undermine a perfectly good day of natural light exposure with unnatural light after dark.¹⁷ This is so common that experts have a name for it: light-induced melatonin suppression, or LIMS.

Melatonin’s role in sleep is just the beginning. Melatonin performs a variety of functions in the body, making it indispensable for a long and healthy life. Melatonin has antioxidant properties, meaning it fends off damaging free radicals in our bodies, thus protecting us from a range of maladies, from migraines to deadly neurodegenerative disorders like Alzheimer’s.¹⁸ Melatonin also enhances our immune systems, and appears to be protective against a variety of cancers, especially breast and prostate cancer.¹⁹ Melatonin receptors are present in many parts of the body, including the blood vessels, ovaries, and intestines. Melatonin appears to help regulate reproductive hormones in women through its interactions with the ovaries and pituitary gland. Melatonin even influences the timing, frequency, and duration of menstrual cycles. Melatonin, in nonhuman mammals at least, also helps to cue mating.

Serotonin is the daytime neurohormone, but don’t think of it as the functional polar opposite to the nighttime melatonin. Cortisol plays that role. Like serotonin, cortisol production is stimulated by exposure to bright light such as sunlight and is the primary hormone for getting us awake and going in the morning.²⁰ It’s healthy and normal to have elevated cortisol levels in the early to midmorning, but not beyond. We all require a strong, well-timed cortisol rhythm, where cortisol rises sharply from early in the morning (just prior to sunrise), peaks around midmorning following bright sunlight exposure (while melatonin is low), then drops away over the remainder of the day and into the evening (as melatonin begins to rise once again in the absence of bright light). When the rhythmic interplay between cortisol and melatonin is disturbed in any way, particularly chronically, our bodies pay a high price. We’ve already mentioned how chronically elevated cortisol is disruptive, causing premature aging and visible belly fat deposits in chronically stressed people, both sedentary folks and recreational athletes alike. Many aspects of modern life serve to elevate cortisol and/or suppress melatonin at inappropriate times, be it many of the common low-calorie diets, badly timed and/or excessively long fasts, excessive exercise (think: Jill’s excessive HIIT regimen), shift work (and the associated circadian rhythm disruption), the stress of overscheduled lives, or even the anxiety of scrolling through social media, a common pre-bedtime routine for many (note: feeling pressured to project the right image on social media, or trying to equal or surpass the projected images of others, isn’t optimal for inducing a blissful nighttime repose). Comparison isn’t relaxing, and social media has a comparative aspect programmed right into it. All of these things serve to elevate cortisol as a part of our stress responses to life’s daily pressures.

With a basic sense of the underlying neurology in place, we’re now in a much better position to understand the devastating impact that a lack of daytime bright natural light exposure can have. Recent research has suggested that spending too much time in relatively low-light rooms could be changing the way our brains process information and impairing the growth of new neural connections. “Are Dim Lights Making Us Dimmer?” read the headline of one report I reviewed.²¹ Our increasingly indoor lifestyles are also thought to be behind the global nearsightedness (myopia) epidemic, where up to half of young adults in the United States and Europe, and upward of 90 percent of Asian teenagers are affected—a massive change from a half-century ago. The strongest environmental risk factor for this large-scale loss of visual acuity across our populations of teenagers and young adults: the lack of bright natural light exposure associated with being indoors most of the day.²²

Perhaps the best example of the impact a lack of bright light exposure can have on our psychological health comes from looking at those who suffer from the winter blues: seasonal affective disorder (SAD) and its milder variant, subsyndromal seasonal affective disorder (SSAD). SAD/SSAD is a form of depression that’s related to light changes in the seasons, most commonly autumn and winter, but is known to also occur in spring and early summer. There seems to be a clear link between light exposure and a change in our mood, outlook, and well-being.

We know that many animals change their behaviors in the winter months as the light wanes, with some going into complete hibernation. A decline in serotonin levels with the reduced light exposure (both duration and intensity) and a concomitant increase in daytime melatonin levels, often in conjunction with dietary factors such as an insufficient specific amino acid intake, is at the heart of the winter blues we can often feel ourselves slip into.²³ Living far from the equator appears to be a key risk factor for experiencing seasonal affective disorders, further supporting the suggestion that changes in natural light exposures are fueling this phenomenon. Indeed, in high-latitude regions such as Finland and Alaska, around one in ten people are affected by SAD, and one in four by SSAD.²⁴ Compare this to fewer than two in one hundred people in Florida.²⁵ Seasonal mood disorders are also more pronounced in regions that suffer cloudier winters, further reinforcing the notion that light plays a key role in our mood and feelings of well-being.

Symptoms of winter-onset SAD include low energy levels, tiredness, cravings for high-carbohydrate foods (driving increases in body fat), sleeping problems, difficulty in concentrating, feelings of hopelessness or worthlessness, and suicidal ideation. Rather than depression, summer-onset SAD, driven by excessive light exposure (such as might be experienced during the “white nights” of high-latitude countries in the summer months), is more likely to be characterized by anxiety and mania. The easily overstimulated, hyperactive, and obsessive-compulsive tendencies that accompany summer-onset SAD are more commonly associated with unhealthy weight loss rather than weight gain.²⁶ These extremes give us insight into the effects of light—too little, too much, poorly timed—on our mood and behavior. While both winter- and summer-onset SAD may represent extremes, most of us function and experience variances in our moods along a continuum of light exposures. It’s hard not to observe that rates of depression and anxiety are increasing as our light and dark exposure patterns are perhaps at the most extreme they’ve ever been in human history.

Insufficient bright light exposure not only leads to low serotonin levels and poorly timed cortisol pulses, but as bright light exposure also catalyzes dopamine synthesis, a lack of well-timed bright natural light can also lead to low dopamine levels.²⁷ Dopamine is our motivation, pleasure, and mood neurotransmitter, and is part of a system all too readily hijacked by modern life. Think about the overabundance of drugs, alcohol, pornography, gambling, and processed food. What propels us to seek out sunlight, and what’s responsible for the euphoric feelings we get once we are in it? Dopamine. Knowing this, it should also come as no surprise that shopping mall display lights are set significantly brighter than the lighting in other areas.

The symptoms of low dopamine include low mood, fatigue, apathy, a lack of motivation, an inability to concentrate, that “I can’t be bothered feeling,” and cravings for highly rewarding foods containing sugar, fat, and salt. Reread the symptoms of winter-onset seasonal affective disorder above. Sound familiar?

Rediscovering the Dark Side—and the Light

For the vast majority of our evolutionary history, we have remained connected to and synchronized with the planet’s natural light and dark oscillations, including the slow and steady ebb and flow of these cycles across the seasons. Despite the invention of the electric incandescent bulb, natural light and complete darkness still represent the two most powerful influences on our circadian biology. The consequences of our inverted light exposure are immense, traversing nearly every aspect of our biology. Yet most of us, most of the time, remain ignorant of the profound impact that light and darkness have on us. We resign ourselves to low mood, low energy, and bouts of anxiety and depression, because, well, that’s just modern life. That’s just the way it all is. But I don’t buy that story.

By becoming more aware of the effect our light exposure patterns have on us, we can become unstuck in many areas of our life. For example, do you find yourself craving sugar, especially after dinner? By staying up late at night in the presence of artificial light, we give our bodies the message that it is daytime in the summer. This not only inhibits melatonin production, but it causes us to crave more sugar, as we’re adapted to do during summer. But perhaps one of the surprising takeaways from this chapter is that a lack of early bright light exposure has the same effect. Experiment on yourself over a few weeks and see whether early light exposure influences your sugar cravings throughout the day. For those lucky few of you who don’t have a sweet tooth, expose yourself to light and see whether you notice a difference in your energy or mood levels (indications you might have experienced more restful slumber). You can begin to develop self-awareness and intuition by simply asking, “How do I feel in the morning?” and reflecting on the response. You’ll be better equipped to notice midafternoon energy slumps—perhaps as in Jill’s case, addressed with sugar and caffeine—as well as anxiety and depression, both of which are linked with circadian dysregulation.

Whether we’re trying to subdue our sugar cravings, increase our energy, rid ourselves of our abdominal fat, improve our mood, or get our lives and health “unstuck,” we need to start with sleep. Become more aware of your sleep and light/dark cycles, and you’ll find that your diet and physical activity levels will improve in concert, as will your emotional balance and natural connections with others. As kids, we might have been afraid of the dark. As adults, we’re still afraid of the dark, but for a different reason: stuck on summer sleep patterns, we fear the lack of dopamine-releasing light indicating that someone has liked our Instagram status. We have the fear of missing out (FOMO), but that fear makes us treat our bodies in unhealthy ways. It’s time that we paused to refamiliarize ourselves with nighttime darkness and daytime light, embracing the many health, longevity, and emotional benefits that come when light and darkness are in their natural balance. As best we can, we need to brighten our days and darken our nights.