Rhythm. It‘s the basis of life. The earth rotates on its axis and revolves around the sun, bringing us the progression of days and seasons. The tides ebb and flow, crocuses open to the light, a caterpillar becomes a butterfly. Here on Earth, plants, animals, and even some types of fungi attune to a 24-hour (circadian) rhythm. Our bodies are cued to awaken when the sun comes up and wind down as the sky darkens.
But what about people who live it up when the sun goes down? Or those who work the night shift? These questions have been the subject of studies over the past decade as an increase in melanoma has led to suggestions that the cause might be our increased use of artificial light at night.
Seeing the Light
Electric lighting proved to be a huge boon to industry when it came on the scene early in the 20th century, extending productivity by up to seven hours. But it's now been shown to have a profound effect on our circadian rhythm and a wide variety of physiological processes.
One of the early definitive studies, appearing in 2006 in the Indian Journal of Medical Sciences, demonstrated that light at night (LAN) can suppress production of melatonin, a hormone that regulates the body's biological clock. When the process works properly, the absence of light triggers melatonin production, which down-regulates the body so that sleep and repair can begin.
"During sleep, our tissues are repaired," says Emily Kane, ND, LAc. "Sleep is the most important thing. The inner lining of our arteries, for example, requires » daily repair. Nature lays down a light layer of cholesterol in our arteries as a sort of band-aid. The nucleus of the cell has a double layer of cholesterol as protection. During sleep, the lining of the blood vessels gets smoothed out. But if we keep irritating it and not getting enough sleep to repair it, the cholesterol builds up."
From the standpoint of Chinese medicine, life energy moves through a cycle of 14 different energy and organ pathways. Each pathway functions in two-hour blocks as the energy reaches and moves through it. Kristen Bobik, DC, LAc, explains that the stomach, for example, is most active form 7-9 a.m., so that's the best time for breakfast. The heart is strongest between 11 a.m.-1 p.m., so that's good for exercise. And the liver, the body's detoxifier, is most active form 1-3 a.m. "We need to rest then," says Bobik, "so the liver can do its job."
The Dark Side
"We should live in darkness at night," says Abraham Haim, PhD, head of the Center for Interdisciplinary Chronobiological Research at the University of Haifa, Israel, in an article in Israeli Innovation News. "But since early evolution, humans wanted to change the darkness. So we need to ask what type of illumination is less harmful."
As Haim implies, not all lighting is created equal. Cells in the retina that project to the circadian clock in the brain are most responsive to white LED light, which is emitted at short wavelengths of 440-500 nanometers. A 2011 study showed that this type of light suppresses the body's production of melatonin five times more than the orange-yellow light from high-pressure sodium (HPS) bulbs, used for street lamps and security lighting.
Back on the Cycle
So should we all adopt a wilderness routine, rising with the sun and retiring with the moon? Should we turn off the lights and relax by candlelight? Experts agree that it's wise to minimize our exposure to artificial light at night-within reason. "Melatonin begins production generally around 9 p.m.,"
says Bobik. "It's not logical to think we can shift entirely to a dawn-to-dusk rhythm, although that would be ideal, but we definitely can go to bed earlier."
This is a notion that Kane, and many others, second. "Sleep architecture is such that it's ideal to get your first two hours of sleep before midnight," Kane says. "Sleeping from 10 p.m. until 2 a.m. will enable you to do okay the next day. Add the period from 3-6 a.m. to be healthier, more pleasant, and more productive. And then sleep one more hour, until 7, for optimum health."
Flip the Switch
Experts agree that use of the computer should be limited to 15 minutes maximum during the three-hour period before bed. But the jury is still out on TV. It may be acceptable, say researchers at the Lighting Research Center at Rensselaer Polytechnic Institute in New York, because the amount of light exposure is minimal unless you crowd the screen.
Experts also advise keeping a nightlight in the bathroom unless it's easy to get to in the dark. Flipping on the main bathroom light for even a few minutes can disrupt melatonin production. And eliminate or minimize artificial light in the bedroom, including alarm clocks, cable TV indicators, and surge protectors.
There's one more tip as well, according to the experts at Rensselaer: Get some sunlight. Daylight is as important to a normal circadian rhythm as darkness. Rather than sitting in an office all day and eating at your desk, go outside for 15 minutes, preferably at the same time each day. That kind of regular exposure gives the body a clear signal that it's daytime. And then, when sky darkens and your eyes begin to droop, you'll be in perfect rhythm-and optimum health.
Recent sleep studies in Israel and Switzerland compared the effects of incandescent light bulbs (the old-fashioned kind that are being phased out for more energy-efficient varieties) with short-wavelength LED lighting. Subjects in each group were exposed to one type of lighting or the other for two hours in the early evening. Those exposed to the incandescent bulbs, which emit at wavelengths of 550 nanometers or greater, experienced no reduction in normal nighttime drowsiness or melatonin production.