Coffee after three consecutive nights of sleep deprivation may not work, warn scientists

Scientists have warned that people's reliance on the morning latte or Americano to pick them up after regularly denying the right amount of sleep will not work.

According to researchers, restricted sleep was five hours a night or less of sleep.

Two cups of coffee would help people wake up and boost their performance, according to experts, but a new study had found after three consecutive nights of restricted sleep caffeine lost its effect.

Researchers found that after three consecutive nights, caffeine could no longer improve a person's alertness or performance.

The findings revealed that relative to a placebo, caffeine significantly improved a person's Psychomotor Vigilance Task (PVT) performance during the first two days.

Lead author, Dr Tracy Jill Doty, of the Walter Reed Army Institute of Research, said: 'We were particularly surprised that the performance advantage conferred by two daily 200mg doses of caffeine was lost after three nights of sleep restriction.

''These results are important, because caffeine is a stimulant widely used to counteract performance decline following periods of restricted sleep, www.telegraph.co.uk reported.

''The data from this study suggests that the same effective daily dose of caffeine is not sufficient to prevent performance decline over multiple days of restricted sleep.''

Tests have revealed three nights in a row of five or less hours of sleep a night and coffee could no longer help with alertness and performance

The study, which was a double blind placebo-controlled one, involved 48 healthy participants.

The subjects had their sleep restricted to five hours a night over five days and received a twice daily 200 mg of caffeine or a placebo.

A shot of espresso contains 75 mg of caffeine while a regular cup of strong coffee contained around 200 mg.

The participants were required to perform a set of cognitive tasks hourly while awake and a modified Maintenance of Wakefulness Test was administered six times per day.

Results showed that compared to the placebo, caffeine significantly improved Psychomotor Vigilance Task performance during the first two days, but not in the last 3 days of sleep restriction.