The 4 Season Solution. Dallas Hartwig

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.

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      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.