It is something we are all guilty of, burning the candle at both ends only to reach for that essential hit of caffeine first thing.

And while it may work as a once off, scientists have warned relying on your morning latte or Americano throughout the week will not work.

They found after three nights of disturbed sleep, caffeine loses its effect.

Researchers defined restricted sleep as five hours a night, or less.

And it was at this point, after three consecutive nights, that they found caffeine can no longer improve a person’s alertness or performance.

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

But, researchers found the benefits were lost in the last three days of restricted sleep.

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.

‘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.’


Researchers analyzed 48 healthy individuals who participated in a double blind, placebo-controlled study.

Those taking part were not allowed any more than five hours sleep a night, for a total of five days.

Participants were given either 200mg of caffeine or a placebo twice a day.

Researchers then performed a series of tests with the study volunteers.

A cognitive task battery was undertaken hourly during the day and included a 10-minute PVT, a profile of mood states, and the Stanford Sleepiness Scale was also measured.

In addition, six times a day, participants took part in a modified Maintenance of Wakefulness Test.

The findings, published recently online in the journal Sleep, were presented today at SLEEP 2016, the 30th anniversary meeting of the Associated Professional Sleep Societies.