Readers are better off with an old-fashioned book at bedtime instead of an electronic reader, which scientists say can seriously disrupt the body's internal clock and throw the cycle of sleep and wakefulness into disarray.
Many people read books at bedtime and with e-readers growing in popularity, a team of Harvard scientists embarked on an investigation to assess the technology's impact on the brain. They found it isn't benign.
Led by Dr. Anne Marie Chang, a neuroscientist formerly of Harvard's Brigham and Women's Hospital, medical investigators revealed that electronic device exposure within four hours before sleep not only disrupted the ability to fall asleep but also affected the ability to remain alert the next day.
Electronic devices, Chang said, emit extremely bright light in the short wavelength or "blue" region of the spectrum. Blue light is so bright it's capable of blocking melatonin, the sleep hormone, which the body's circadian clock naturally times to flow at night, she said.
Lauren Hale, a professor of preventive medicine at Stony Brook University and founding editor of Sleep Health, a journal devoted to sleep research, said the Harvard study provides concrete evidence that reading from an electronic device has a disruptive effect.
"The Chang study is very well-executed and focuses on the role of light," said Hale, who was a researcher in a similar but unrelated study in 2011.
Hale and colleagues found that texting on a cellphone or watching TV in the hour before bedtime has a disruptive effect on sleep. That study relied on participants recalling how much time they spent with an electronic device before bedtime.
But Chang and her team hospitalized 12 people and had them read on an iPad for five consecutive nights, then from conventional books for another five. Although iPads were used, Chang extrapolates her findings to other e-readers, laptops, cellphones and LED monitors, which also emit blue light.
"Blue light is in the wavelength of about 420 to 500 nanometers," said Chang, now an assistant professor at Pennsylvania State University. "That's the same wavelength of many modern-day bulbs that have enriched light and are also in this part of the [light] spectrum," she said of energy-efficient bulbs.
Earlier unrelated research had shown blue light suppressing melatonin, Chang said, but little was known about the effect of e-readers on the body's circadian rhythms, the internal system that times the flow of hormones and the oscillation of countless physiological functions within 24 hours.
Chang's study, reported in Proceedings of the National Academy of Sciences, taps into a deep well of research that in recent years has linked circadian disruptions to cancers, heart disease, diabetes and obesity.
"Circadian disruption can have multiple effects on health," said Dr. Harly Greenberg, who heads sleep medicine at Long Island Jewish Medical Center in New Hyde Park. Greenberg added research involving shift workers revealed they are more likely than day workers to develop certain forms of cancer, particularly breast and prostate.