Jason Lauritzen

Light is a ubiquitous health variable that few understand and many dismiss. Why does light deserve our attention? Consider this: every cell in your body is tied to CLOCK genes. The name fits these genes — they act like little cellular clocks, keeping track of the time of the day. Their primary environmental time cue is light. Your body has trillions of cells, which means it has trillions of clocks. They communicate with one another to keep track of your circadian rhythm, which ultimately governs every aspect of your biology, from body temperature to hormone regulation to cell regeneration. The master timekeeper of these trillions of clocks that keeps everything in sync is a mass of 20,000 nerve cells in the hypothalamus of your brain called the suprachiasmatic nucleus (SCN). Given that coordination between cells (and, in turn, their clocks) is so crucial, it’s unsurprising how research continually turns up health problems tied to disorders in circadian rhythm. Did you know that Proper sleep suppresses inflammation via the BMAL1 CLOCK gene? When CLOCK genes like PER2 and BMAL1 get uncoupled, lung tumor formation is more likely? If CLOCK genes like BMAL1 and REV-ERBα don’t function correctly, cells can’t rest, which allows cancer to replicate more quickly? Artificial blue light — regardless of time of day — alters glucose metabolism (blood sugar) and sleep cycles? There is a specific field in medicine — called chronopharmacology —that looks at the interactions between drugs and CLOCK genes. Timing matters when introducing agents into biological systems. For example, did you know that whether a mouse administered e. coli lives or dies depends on the time of day of the injection? The simplest analogy to your body’s circadian rhythm is a symphony. The orchestra are your trillions of cells. The conductor is the SCN. When everything sync ups, you get a beautiful song — the composer’s intent. When people start playing in different times, out of tune, etc., you lose the song entirely. With an actual symphony, the toll paid for an “off” performance is a bad song. When it comes to biology, the penalty is poor health and disease states — whether it be cancer, more inflammation and/or altered blood glucose levels — as some of the research bullet points above show. Understanding Sleep/Wake Cycles. Much of the research on circadian rhythm focuses on melatonin, a hormone produced in your pineal gland that helps regulate your sleep, causing drowsiness at appropriate times. It should be noted that while melatonin has been called “the chemical expression of darkness” and makes sure you enter proper sleep cycles at night, it relies on light/dark cues processed by your SCN. If melatonin (via the SCN) helps regulate sleep, what helps with wakefulness? That’s the role of cortisol. There’s such a surge of it first thing in the morning that that we have the term cortisol awakening response. After this surge, it slowly drops and levels off throughout the day. In a normal person under close-to-natural conditions, you get these two bell curves you see below, with cortisol peaking in the morning and lowering toward evening, and melatonin peaking in the evening and lowering throughout the day. How does the melatonin portion of the above chart play out at the CLOCK level? Foster and Kreitzman note in their book, Seasons of Life: There is a very high density of melatonin receptors in the individual cells of the pars tuberalis (PT). Melatonin binds to these receptors, which alters the gene expression of several of the clock genes, including the Per and Cry genes … within the cells. … Cry gene expression tracks melatonin rise (dusk), whereas Per gene expression tracks melatonin decline (dawn). Light: Then and Now. Notice how above the melatonin and cortisol chart, I used the words “close-to-natural conditions.” That was intentional. Up until Edison patented and commercialized the light bulb in the 1880s, we, as a species, were used to light from the sun during the day and darkness at night, or minimal, man-made light sources like candlelight and gas lamps at night, thus living under close-to-natural conditions dictated by the rising and setting of the sun. The above picture from space shows our current nighttime reality. 54 percent of the world’s population lives in urban areas — the major source of this severe light pollution — and that number is expected to grow to 66 percent by 2050. Research has found that 80 percent of the world’s population lives under light-polluted skies. If you narrow this down to just the United States and Europe, the number climbs to 99 percent. The virgin night sky is now so foreign to the majority of individuals that it requires going to a very remote area or a major event like a blackout to experience the night sky as intended. The light landscape changed drastically in a very short period of time. Instead of sunlight during the day and darkness at night, most of us are bathed in artificial light almost 24/7. What colors are now most prevalent? If you compare the visible spectrum reference chart below to common artificial light sources above, you’ll notice we’re getting a unbalanced surplus of violet, blue, and to a lesser extent, green. Popular devices like iPads and iPhones feature these same peaks in the violet (380–450 nm) and blue range (450–495 nm) that we see from other artificial light sources. Melatonin: The Chemical Expression of Darkness. 90 percent of Americans use light-emitting electronics within one hour of bedtime. Exposure to violet, blue and even green light (495–570 nm) after sunset has two primary effects: melatonin suppression and phase shifting or re-tuning. Let’s cover melatonin first. As noted in the section above, melatonin helps regulate sleep. It should be obvious, but it must be stressed: we are meant to have complete darkness at night. Cell phones, tablets, TVs, overhead lights, lamps, LEDs, etc., are not natural. This is why studies continually find that violet and blue light suppress melatonin production the most. For example, something as seemingly innocent as room light can reduce pre-sleep melatonin levels by 71.4 percent and daily melatonin levels by 12.5 percent. This suppression effect is much greater in children than adults. As you move further away from violet and blue (380–495 nm) toward green (495–570 nm), yellow (570–590 nm) and orange (590–620 nm) spectrum, the melatonin-suppressing effects aren’t nearly as great. Green light is about one quarter to one half as potent as blue, and yellow, orange and red have next-to-no effects on melatonin. If you’ve been clicking on the research links, you’ll notice several mention the term “lux.” This is shorthand for saying the total amount of visible light present and its intensity on a surface. The higher the lux, the more intense the light source. Complete darkness would be zero lux. As you can see above, something like a night without a full moon is only 0.002 lux. Compared to a moonless night, a typical living room light is 2,499,900 percent more intense. No, that number was not a typo. Combine intensity (lux) with these violet, blue and green ranges (380–570 nm) and you’ve got a potent cocktail. Higher lux values amplify the damaging effects of these nanometer ranges. That’s why — if you go back to the previously cited study — you see a 301 percent increase in melatonin suppression between the 15 lux and 500 lux control groups. When melatonin levels are disturbed and start to drop, the sleep/wake cycle is thrown into disarray and your body can’t properly utilize autophagy—an essential cellular maintenance and cleanup process. Melatonin is critical not only for this sleep/wake cycle, but the hormone itself Is a more effective antioxidant than vitamin E. Reduces oxidative stress. Makes mitochondria (your cell’s power plants) more efficient. Given the melatonin-suppressing effects of violet and blue light, it should be self evident that if you block that range of light (380–495 nm) from hitting your eyes, you help preserve melatonin levels and thus keep sleep/wake cycles in order. And that’s exactly what the research finds. Keep in mind: most of these studies only look at glasses that block violet and blue (and some green). We would expect glasses that additionally block all green to have even more benefits. Excuse Me: What Time Do You Have? When your circadian rhythm is running correctly, you can say you have a normal phase response curve.However, as you learned in the previous section on melatonin, violet, blue and green light start to shift sleep/wake cycles. Organisms are so sensitive to light that just a single pulse of the wrong kind of light can initiate a process called phase shifting or re-tuning. Like with melatonin suppression, the greater the lux, nanometer range and length of exposure, the greater the phase shift. The developers of f.lux, a light-blocking software, have a handy tool called the f.luxometer that calculates the phase shift potential of different light sources. You may be thinking, “Well, I bet it takes days, weeks, months, heck, even years, before you start to see changes at the genetic level from artificial light and phase shifting.” Sorry to burst your bubble. As noted in the introductory section, every cell is connected to time and the greatest environmental time cue is light. We’re so wired to pick up light, that we can detect a single photon. And all it takes is one night of artificial light throwing off your sleep to alter CLOCK genes and, in turn, affect gene expression. How do we combat this phase shifting? Per the melatonin section, any kind of barrier — like blue-blocking glasses — that stops 380–570 nm of light will help preserve melatonin and help normalize circadian rhythm. If trying to keep things dark (or as close to dark as possible) during the night helps, then the corollary should be true, i.e., sunlight during the day should help, too. That’s exactly what Environmental Health...

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