Lead researcher Prof Charles Czeisler told the BBC News website: “The light emitted by most e-readers is shining directly into the eyes of the reader, whereas from a printed book or the original Kindle, the reader is only exposed to reflected light from the pages of the book.”
He said disrupting sleep in turn affected health.
“Sleep deficiency has been shown to increase the risk of cardiovascular disease, metabolic diseases like obesity and diabetes, and cancer.
“Thus, the melatonin suppression that we saw in this study among participants when they were reading from the light-emitting e-reader concerns us.”
Dr Victoria Revell, who researches the impact of light on the body at the University of Surrey, told the BBC: “This is a very good study and I think it’s really interesting.
“We should be advising people to minimise their [light-emitting e-reader] use in the evening, particularly teenagers who are a group that are using their phones and tablets late in to the evening.”
Teenagers naturally have a late body clock, which makes them slow to rise in the morning and up late at night.
“People who already have a delayed body clock are delaying themselves much further and that is a very important message,” Dr Revell added.
Prof Czeisler agreed, saying there was “special concern” for teenagers who were already sleep deficient by being forced to get up early for school.