Electric lights, including those illuminating laptop computers, smartphones, and tablets, often play a key role in causing people to sleep badly.
Artificial lights disrupt the body’s natural rhythm, affect chemicals in the brain and drive people to use stimulants such as caffeine to stay awake longer, according to Harvard academic Charles Czeisler.
Writing in the journal Nature, the professor of sleep medicine at Harvard Medical School called for research to help develop “behavioural and technical” ways of counteracting the ill-effects of artificial light on modern sleeping patterns.
The decline in the number of hours slept per night is affecting public health, including a greater risk of obesity, diabetes, heart disease, depression, and stroke in adults and concentration problems in children, he said.
While all electric light affected “circadian rhythms” — the natural body clock — and sleep, night-time exposure to LED lights such as those in phones and computers was “typically more disruptive” than standard electric light bulbs, said Prof Czeisler.
“There are many reasons why people get insufficient sleep in our 24/7 society, from early starts at work or school, or long commutes, to caffeine-rich food and drink,” he wrote.
“But the precipitating factor is an often unappreciated, technological breakthrough: The electric light.
“Without it, few people would use caffeine to stay awake at night. And light affects our circadian rhythms more powerfully than any drug.”
Between 1950 and 2000, the average person increased their use of artificial light sources by four times, with a parallel rise in sleep deficiency, Prof Czeisler said.
Artificial light inhibits sleep-promoting neurons and the nightly release of the hormone melatonin, which aids sleep, while activating neurons that boost alertness, he said.
It fools the brain into delaying its “second wind”, which kicked in during the afternoon to see people through to sunset before electric light was invented, until much later in the day.
He said that as a result of modern technology “many people are still checking email, doing homework or watching TV at midnight.”
In a study, 30% of working adults in the US and 44% of night workers reported getting less than six hours sleep a night on average.
Fifty years ago less than 3% of the US adult population slept so little.
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