30 Jun Caffeine loses it effect after three days of sleep restriction.
Military research from the USA has shown that chronic sleep restriction causes caffeine to become less effective. The study included 48 healthy volunteers who had their sleep limited to 5hrs a night, you should typically get between 7-9hrs per night. All participants had their mental performance tested every hour during the day. One group took 200 milligrams of caffeine which is close to two strong coffees worth of caffeine, and the other group took a placebo that would do nothing. What they found was that during the first couple of days, the caffeine improved the first group’s performance. However after three days of sleep restriction, the performance advantage that the caffeine group had was lost. There was no longer any improvement in this group after taking caffeine. I certainly have had those days where the caffeine has barely done a thing, perhaps I have been sleep restricted and need to get a good night’s sleep more than I need another coffee!