• Sleep debt is real, and coffee can only do so much to combat it.
A new study has found caffeine can only fight the effects of sleep deprivation for so long.
Alyssa Braithwaite

18 Aug 2016 - 1:03 PM  UPDATED 18 Aug 2016 - 2:35 PM

After a bad night's sleep, the first thing many of us do is reach for a strong cup of coffee to help us rise to the challenges of the day.

The bad news is those late nights will catch up with you. A new study has found after just three nights of bad sleep, caffeine has "little to no benefit". 

Researchers from the Walter Reed Army Institute of Research have found that alertness, performance and mood sustainability deteriorated after three days despite caffeine use.

"Sleep debt is real," said the study's lead author, research scientist Tracy Doty told Ozy.

"Every night you're not sleeping, you're building up increased sleep debt, and the same amount of caffeine is no longer effective."

The study, which was presented at SLEEP 2016, the annual meeting of the American Academy of Sleep Medicine and the Sleep Research Society, looked at 48 adults who got just five hours of sleep a night for five days in a row.

Participants were given either 200mg of caffeine - approximately the amount found in a large cup of coffee - or a placebo twice daily in the double-blind study.

They then undertook a series of tests related to mood, sleepiness, wakefulness and reaction time, as well as hourly cognitive tests.

While the caffeinated group had faster reaction times than the placebo group during the first two days, after three nights the participants' alertness and their performance on the tests fell, even after they had they had been given the caffeine.


"We were particularly surprised that the performance advantage conferred by two daily 200 mg doses of caffeine was lost after three nights of sleep restriction," Doty said in a statement.

"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."

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Furthermore, those who took the caffeine reported feeling sleepier and more irritated than those in the placebo group in the final two days of the study.

However, Doty said the study didn't take into account that sleep-deprived people might increase their caffeine intake over time.

"We do not know what would occur if more caffeine was taken," she told LiveScience.

"Increased caffeine dosage will increase negative side effects such as jitteriness, but we do not currently know if an increased dosage would prevent performance decline."

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