Watch Using certain e-readers or tablets in bed late at night leads to poorer quality sleep, a recent study from Harvard Medical School found.

The study found that blue light emitted by electronic devices lowers the production of melatonin, the hormone which regulates sleep.

During the study those using e-readers and tablets instead of books took one and a half hours longer to fall asleep. Their R.E.M sleep, which is critical to memory consolidation, was also shortened.

Despite having the same amount of sleep, those using light-emitting electronic readers felt groggier and more tired during daytime than those who read a book before bed.

Scientists advised people to minimise the use of such devices before bedtime, especially teenagers who need more sleep than adults..