In the frenetic, coffee-fuelled lives of today, too many people are not getting enough sleep. Modern light-emitting diodes (LEDs) used in energy-efficient lighting as well as television and computer screens, laptops, tablets and various handheld devices, are adding to the problem, according to an article appearing today (May 23) in Nature.
Lack of sleep takes its toll. “The cumulative effects of sleep loss and sleep disorders have been associated with a wide range of deleterious health consequences including an increased risk of hypertension, diabetes, obesity, depression, heart attack and stroke,” noted a 2006 report from the U.S. Institute of Medicine.
The electric light has had a powerful impact on the body’s clock, known as the circadian rhythm. “And light affects our circadian rhythms more powerfully than any drug,” remarked Charles A. Czeisler in his perspective article in Nature’s Outlook feature on sleep. He is a sleep specialist with Harvard Medical School and Brigham and Women’s Hospital at Boston in the U.S.
Apart from rods and cones needed for vision, the eye’s retina also contains ‘intrinsically photosensitive retinal ganglion cells’ (ipRGCs). These light-sensitive cells help synchronise the body’s circadian rhythm to the natural day and night cycle.
When artificial light strikes those cells, the body gets misled and responds by promoting wakefulness and inhibiting sleep.
Consequently, “many people are still checking e-mail, doing homework or watching TV at midnight, with hardly a clue that it is the middle of the solar night,” observed Dr. Czeisler. “Technology has effectively decoupled us from the natural 24-hour day to which our bodies evolved, driving us to go to bed later. And we use caffeine in the morning to rise as early as we ever did, putting the squeeze on sleep.”
White light emitted by LEDs was typically rich in blue light. This mattered because ipRGCs were most sensitive to blue and blue-green light. So night-time exposure to LEDs was typically more disruptive to circadian rhythms and sleep than the old incandescent light bulbs.
Since solid-state light fixtures could carry multicoloured LEDs, it would be relatively easy to control their light intensity and colour composition. “The adverse effects of night-time light on sleep and circadian rhythms can be reduced by replacing blue-enriched light with red- or orange-enriched white light after sunset,” he suggested.
In addition, “it is critical to establish a regular bedtime and wake time,” said Dr. Czeisler in an email. The interval between those two times must allow a person to catch enough sleep. An average adult needed eight hours of sleep. Children needed more sleep. A typical high school student would need more than nine hours in bed.
“Children become hyperactive rather than sleepy when they don’t get enough sleep, and have difficulty focusing attention, so sleep deficiency may be mistaken for attention-deficit hyperactivity disorder (ADHD), an increasingly common condition now diagnosed in 19 per cent of U.S. boys of high-school age,” he pointed out in the article.