The 4 Season Solution. Dallas Hartwig

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.