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.

Short Sleep: A Dose of Perspective on the Risks

A woman attending a talk I gave on insomnia was worried about developing Alzheimer’s because she wasn’t getting enough sleep.

“Sometimes I sleep only 4 hours a night,” she said, “and I’m really lucky when I get 5.”

There’s a lot of talk these days about the health risks that accumulate if we sleep less than 7 or 8 hours a night. But reports that appear in the popular media can make the risks sound greater than they actually are.

short sleep may increase the risk of health problems but not that muchA woman attending a talk I gave on insomnia was worried about developing Alzheimer’s disease because she wasn’t getting enough sleep.

“Sometimes I sleep only 4 hours a night,” she said, “and I’m really lucky when I get 5.”

After the talk I asked for details. Did she have trouble falling asleep? No. Did she wake up frequently at night? No again.

“When I fall asleep,” she said, “I’m out cold.”

What about her energy and alertness during the daytime? I asked. Did she feel tired, out of sorts, or foggy in the brain? No, no, and no. Then what was the problem?

“I read online that you’re supposed to get 7 or 8 hours of sleep,” she said, “but I can’t, no matter what. I read that people who don’t sleep enough get Alzheimer’s, and I don’t want to. I want more sleep.”

The Elusive 7 or 8 Hours

There’s a lot of talk these days about the health risks that accumulate if you sleep less than 7 or 8 hours a night.

  • Cardiovascular Disease. Short sleep (sometimes defined as less than 6 hours of sleep a night, and other times defined as less than 5 hours of sleep a night) is linked to increased blood pressure and hypertension, and a greater risk of heart attack and stroke.
  • Cancer. Short sleep duration makes you more vulnerable to breast cancer, colorectal cancer, and prostate cancer.
  • Dementia and Alzheimer’s. A study of healthy older adults found that short sleep was associated with greater age-related brain atrophy and cognitive decline. Another study found that short sleep and poor sleep quality were associated more beta-amyloid in the brain (the main component of the amyloid plaques found in Alzheimer patients).

No wonder short sleepers are worried these days. Who wants a sentence of any of these illnesses hanging over their head?

Interpreting the Numbers

If you read reports of studies that appear in the popular media, it’s easy to misinterpret the results. Let’s say you learn that people with insomnia (who may be short sleepers and who also experience daytime impairments) are twice as likely to develop depression as people who sleep well (research has shown this to be true). “Twice as likely” might make it sound as though if you have insomnia, your risk for developing depression is pretty high.

But often missing from these reports is mention of the actual number of people who do develop depression at some time in their lives—information that could help you put the study results in perspective. Let’s say the lifetime risk of developing major depression in the US is about 17 percent (as shown in a study by Blazer et al in 1994). This figure, which would include both people with and without insomnia, indicates that most people—83 in 100—will never experience major depression in their lifetime.

Now let’s imagine (because I haven’t been able to lay my hands on actual figures) that among people who sleep well, the lifetime risk of developing major depression is 12 percent. If people with insomnia are “twice as likely” to develop depression, then 24 percent of insomnia sufferers will go on to develop major depression at some time in their lives, and 76 in 100 will not. In other words, your odds of dodging the bullet are 3 to 1 in your favor. “Twice as likely” does not sound so bad after all.

Minimizing Risk

I don’t mean to downplay the significance of research exposing links between short sleep or insomnia and increased vulnerability to Alzheimer’s or any other illness. If sleeping less than 5 or 6 hours compromises health, we need to know it, and to understand why and how to minimize the risk.

I am suggesting that the results of these studies may not be as alarming as they seem at first glance. Beyond that, if they cause you to worry about your sleep, they do more harm than good. How long you sleep is determined in large part by genetic factors resistant to change. And—let’s face it—the last thing you need is one more worry to shorten your nights still further.

So what’s the secret to healthy aging if you clock 5 or 6 hours of sleep at best? You’ve heard it time and time again: get as much sleep as you can, eat healthful meals, and exercise daily.

If you’re a naturally short sleeper, what concerns do you have about your health?