Some people have the habit of reading before bedtime, thinking it might help them fall asleep. A recent study, however, revealed that reading e-books at night may damage a person's sleep and health.

Exposure to light-emitting screens during nighttime affects the production of melatonin, the hormone in our body that controls sleep. This disturbance causes a shift in a person's circadian rhythms.

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Circadian rhythms coordinate our body behavior daily and act as a body clock. What makes this possible is the body's response to the light and darkness surrounding it.

Electronic devices emit "short-wavelength-enriched" light, which has a higher concentration of blue light than what composes natural light, said Anne-Marie Chang, assistant professor of biobehavioral health at Penn State and one of the authors of the study.

The research team studied the behavior of 12 adults for two weeks, taking note of differences between those who read from a light-emitting device and from a printed book. Results revealed that individuals who read from electronic devices lacked deep sleep during the night.

These participants found it difficult to sleep during bedtime but became sleepier and less alert the following day. They also had reduced melatonin levels and their circadian rhythms shifted to a later timing. Sleep deficiency may seriously affect people's health, occupation and lifestyle.

Among all gadgets measured by the researchers, iPad was found to be the brightest. The iPad comes with a backlit display that emits more light exposure than other devices.

Unlike the iPad, Kindle and other e-readers use technology more similar to printed paper, which reflects light instead of directly exposing readers to it.

TagsIpad, Kindle, e-reader, ebook, E-book, bedtime stories, bedtime reading, circadian, circadian clock, melatonin, sleep deprivation, sleep deficiency