London - Snuggling up with a good book in bed has long been seen as a way to wind down at the end of the day.
But scientists have discovered that the millions who read their bedtime stories on an iPad or a Kindle Fire are actually keeping themselves awake.
They found that people who regularly read electronic books before lights out sleep for fewer hours.
This is because the blue glow emitted by the electronic devices can destroy the body’s natural rhythm. All living things have an internal mechanism – known as the circadian rhythm, or body clock – which synchronises bodily functions to the 24-hour pattern of the Earth’s rotation. The clock is regulated by the senses, most importantly, the way the eye perceives light and dark.
This mechanism rules our daily rhythms, including sleep and waking patterns and metabolism. It also determines whether we are a “morning” or an “evening” person.
But the pressures of modern living mean many of us now increasingly work against our body clocks – with disrupted sleep thought to be partly responsible for increased rates of cancer, dementia and diabetes.
During the two-week study, 12 participants read electronic books for four hours before bedtime. The experiment was then repeated with printed books.
The researchers found that those reading on screens were less sleepy in the evening and took longer to fall asleep. They had reduced levels of melatonin, a hormone which plays a role in inducing sleepiness.
And they took nearly ten minutes longer to fall asleep after reading an e-reader compared to reading a printed book. They also had a lower amount of rapid eye movement sleep – a stage thought to be crucial because it is when memories are consolidated.
The study was carried out by Penn State and Harvard universities in the US and published in the Proceedings of the National Academy of Science.
Lead researcher Dr Anne-Marie Chang said screens can have an ‘extremely powerful effect’ on the body’s natural sleep pattern.
She added: “Participants reading a light-emitting eBook took longer to fall asleep and had reduced evening sleepiness, reduced melatonin secretion, later timing of their circadian clock and reduced next-morning alertness than when reading a printed book.”
Dr Charles Czeisler from Harvard University, who contributed to the study, added: “In the past 50 years, there has been a decline in average sleep duration and quality.
“Since more people are choosing electronic devices for reading, communication and entertainment – particularly children and adolescents who already experience significant sleep loss – research evaluating the long-term consequences of these devices on health and safety is urgently needed.” - Daily Mail