Artificial Lighting Harmful to Sleep and Health

We hear a lot about the effects of light on sleep. Light in the evening—especially the blue light emitted by devices with screens—blocks secretion of the hormone melatonin, causing symptoms of insomnia. Low lighting during the day also delays melatonin onset and shortens the night.

Shift work, in which workers are routinely are exposed to light at night and must sleep during daylight hours, is so likely to disturb people’s sleep that the problem has its own name: Shift Work Sleep Disorder.

Not only do unnatural lighting conditions interfere with sleep. More and more evidence suggests that artificial lighting is behind the uptick in modern diseases such as cancer.

Insomnia and cancer are more likely in brightly-lit, urban areasWe hear a lot about the effects of light on sleep. Light in the evening—especially light emitted by devices with screens—blocks secretion of the hormone melatonin, causing symptoms of insomnia. Low lighting during the day also delays melatonin onset and shortens the night. Shift work, where workers are routinely are exposed to light at night and must sleep during daylight hours, is so likely to disturb people’s sleep that the problem has its own name: Shift Work Sleep Disorder.

Not only do unnatural lighting conditions interfere with sleep, say epidemiologists Richard G. Stevens and Yong Zhu. More and more evidence suggests that artificial lighting is behind the uptick in modern diseases, the topic of their recent opinion piece in Philosophical Transactions of the Royal Society of London B.

“It’s a new analysis and synthesis of what we know up to now on the effect of lighting on our health,” said Stevens in a University of Connecticut press release. “We don’t know for certain, but there’s growing evidence that the long-term implications of this have ties to breast cancer, obesity, diabetes, and depression, and possibly other cancers.”

In the Beginning

Humans evolved in an environment where the sun was the sole light source influencing internal circadian rhythms. The rising and setting of the sun determined when they slept and ate; it also set the rhythm for fluctuations in body temperature, gene expression, and hormone production. Sunlight in the daytime and darkness at night kept these systems cycling on a 24-hour day.

But the artificial lighting we spend our time in now is dim and poorly timed. Too little light during the day and too much at night lead to the disruption of circadian rhythms, insomnia, and increased susceptibility to disease.

Artificial Lighting and Cancer

Research suggests there is a relationship between exposure to light at night and breast cancer. Several studies show that women who work at night are more susceptible than women who work during the day. Night work is associated with melatonin suppression and, in women, higher levels of circulating estradiol, a reproductive hormone linked to breast cancer. Changes in the lymphatic system have also been observed.

Population studies, too, suggest a connection between breast cancer and exposure to light at night. Researchers in two studies used ambient light as measured by satellite at night to compare breast cancer risk across communities. They found a correlation between ambient light levels and breast cancer. “This has been tested and confirmed within Israel,” Stevens and Zhu write, “and among 164 countries of the world.”

Studies in molecular epidemiology also point to a relationship between circadian disruption and breast cancer. Long-term exposure to shift work alters patterns of gene expression throughout the body in ways that may increase breast cancer risk. Shift work may be a causal factor in colon and prostate cancers as well.

Do What You Can to Protect Your Health

You may be able to reduce your risk of developing these and other light-related health problems:

  • Get a healthy dose of sunlight during the day. If you can’t, buy a light box and use it.
  • Cut down on screen time at night. If you have a choice between an e-reader and a book, go for the book. Incandescent light is better than the blue light emitted by screens.
  • Use heavy curtains to block out all light sources when you’re sleeping.
  • Use red light if you must have light at night. (See my suggestion for red nightlights.) Firelight is circadian friendly for the same reason: it contains an abundance of red wavelengths.
  • Cut down on red meat to reduce the risk of colon cancer. Epidemiological studies show there is a correlation between eating red meat, which is high in iron, and developing the disease.

Awake in the Middle of the Night

The bed—so sleep experts maintain—should only be used for sleep and sex. People who can’t sleep should get up and do something: iron shirts, look at picture books, plan a backyard stupa. Anything, for God’s sake, but toss and turn among the sheets.

I know I should follow this advice. But every fiber of my body cries out for staying flat on my back.

The bed—so sleep experts maintain—should only be used for sleep and sex. People who can’t sleep should get up and do something: iron shirts, look at picture books, plan a backyard stupa. Anything, for God’s sake, but toss and turn among the sheets.

This bit of advice has always put me off. Especially when I wake up in the middle of the night and can’t fall back to sleep, I’m bone-tired and brain-dead. I can barely face getting out from under the warmth of the covers to go to the bathroom, let alone contemplate walking downstairs, turning on a light and settling down with a book. Every fiber of my body cries out for staying flat on my back.

Making Hay While the Darkness Reigns

But I’ve met insomnia sufferers of the middle-of-the-night-awakening type who decided at some point that they were not going to take their wakefulness lying down.

My former colleague Claudia is a journalist with a greeting card business on the side. She used to lie awake fretting when she couldn’t fall back to sleep. Now when she wakes up at 1 a.m., she goes upstairs to make birthday cards.

“It’s like playing around,” she says. “It takes my mind off everything, and sometimes I think it helps me mellow out a little, too.” After working a couple of hours on her cards – an activity she says is fun but not cerebral – she crawls back into bed again and can usually get a few more hours of shut-eye. She’d rather deal with insomnia this way than take sleeping pills.

Marty is another example. Self-employed, he goes to bed around 9 p.m. and uses the time he’s awake in the middle of the night to work on an online newsletter. “I do my best writing between 2 and 5 in the morning, “ Marty says. Then he goes back to sleep for another hour and a half. He’d like to sleep more, and to get all his sleep at one go, but his body seems to have different needs.

Bimodal Sleep in Nights Past

Historian A. Roger Ekirch claims this pattern of broken sleep was actually common before 1800, when people lived without artificial lighting in their homes. Ekirch has found several references to nights in which people took their “first” sleep from about 9 or 10 p.m. to somewhere past midnight. Then they got up to brew a tub of ale or chat with neighbors, or they stayed in bed to pray, make love or meditate on dreams. At last they fell into a “second” or “morning” sleep that lasted until dawn.

Experiments conducted by sleep researcher Thomas Wehr in the 1990s suggest this bimodal pattern of sleep is the pattern humans might well fall into today in the absence of artificial lighting. Our modern lights-out period lasts for seven or eight hours a day year-round. But in temperate climates in the pre-industrial era, during the winter months when darkness lasted 14 hours, people spent a lot more time in rest and relaxation.

When Wehr re-created these conditions by giving his experimental subjects a 14-hour sleep window, they settled into a routine in which their sleep fell into two distinct periods. One came at the beginning of the “biological” night and one at the end, with a period or periods of quiet wakefulness in between. Wehr concluded that bimodal sleep may actually be more “natural” than the consolidated sleep period that is the norm today.

The notion may not be reassuring to insomniacs unable to turn middle-of-the-night awakenings to their advantage, or whose work or families demand that they be up at the crack of dawn. Nor does it jibe with the thinking of most sleep experts, who suggest that a consolidated period of sleep is for the insomniac the Holy Grail. But if segmented sleep really does come more naturally to some poor sleepers, then the Claudias and Martys may be better off going with the flow.