Light and dark have a direct effect on our hormones, influencing sleep and wakefulness, mood, energy levels and even health. Regulated by a “master clock” known as the suprachiasmatic nucleus (SCN), our bodies are genetically programmed to follow the movements of the sun and the earth, sleep researcher Roger Cole says. But living in the modern world has distanced us from the cycles of day and night, which researchers are finding could negatively affect our health and happiness. By working with our natural rhythms and controlling our interaction with light, we can keep our spirits and energy levels high as the days get shorter.
The SCN, which controls our 24-hour circadian rhythm, is kept in time by the alternating light and dark of day and night. If you lived outdoors, morning light would fall on your retina, signaling the SCN to raise your body temperature, release the hormone cortisol and suppress the hormone melatonin, all of which would help you wake up naturally. Later, when it got dark, the SCN would tell the pineal gland to release a flood of melatonin, making you sleepy. Provided the light is dim, melatonin levels would stay high all night.
Living in a modern house can interfere with these natural rhythms. Even with the lights on, it’s 50 to 100 times dimmer inside than it is outside during the day, Cole says. When the sun goes down, electric lighting can delay the melatonin surge, especially in those of us genetically prone to be night owls. In urban areas, light pollution—the glow created by lights on buildings, cars, signs and more—can prevent or reduce melatonin release and interfere with sleep. But managing the light in your house will help keep you rested and healthy, and maintaining your master clock is deviously simple: Keep your house light when it’s light outside and dark when it’s dark outside.
Sky blue light is the best at signaling your body to reset its clock in the morning. Just 10 minutes of morning sun will do the trick. Read the paper on a sunny porch or start the day with a walk around the block. If your bedroom windows face east or south, Cole recommends leaving the shades open at night so you can catch the sunrise. If you need privacy, consider top-down shades or café-style (half-height) interior shutters so the top of the window is open to the sky. If your bedroom doesn’t have a sunny window, skylights or light tubes could help bring in sunlight. For dark, cold or wet mornings (or if you need to block out nighttime light pollution), consider a sunrise alarm clock—a light that slowly brightens before you wake up—or full-spectrum lights—light boxes designed to treat seasonal affective disorder. (Look for one that’s 5,000 or 10,000 lux and that screens out UV rays; see Resources.) Or use both, setting a timer to switch on the bright light when the alarm clock reaches full intensity.
Research indicates that nighttime exposure to electric light reduces production of the cancer-fighting hormone melatonin, which could negatively affect our health. Studies have found that women who work the night shift, such as nurses and flight attendants, have breast cancer rates 60 percent above average. And a recent study led by researchers at the University of Haifa in Israel found women who live in communities with high light pollution are more likely to get breast cancer than those who live where nights are dark.
To regulate your melatonin levels, decrease your dose of light inside after the sun sets. Avoid bright light in the evening, especially the blue light emitted from television and computer screens and bright white LED and CFL bulbs, Cole says. A few strategically placed lamps with red-hued (Kelvin temperatures from 2500 to 3000), low-watt bulbs are a good bet, especially if they’re on a dimmer. If drastic measures are necessary, go for red darkroom bulbs or wear glasses that block blue light in the evening (lowbluelights.com). If you live in an area where light pollution is a problem, use blackout shades to keep bright light from entering through windows.
Before gas lighting shortened winter’s long nights, people didn’t sleep straight through from sunset to dawn. They slept in two intervals, separated by an hour or more of quiet wakefulness in the middle of the night. Some traditional peoples who live without electricity still sleep in two periods, as do some animals. In preindustrial Europe, people pondered their dreams, prayed, made love or got up and visited during this nighttime waking. A National Institute of Mental Health study found the same pattern: When participants spent 14 hours in the dark every night, replicating winter nights without artificial light, they slept in two segments. The nighttime waking period was unique hormonally, characterized by high levels of prolactin—usually associated with nursing mothers.
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Kathleen Christensen, who has a degree in human biology, uses light and dark to curb her and her daughter’s night-owl and ADD tendencies. Her blog about life with ADD is at Head in the Clouds.