When does the caffeine in coffee stop working?

We like to make up for lack of sleep with coffee. But the latest research has shown when the caffeine in coffee just doesn't help us anymore.

Do you also often make up for lack of sleep with coffee? Extensive new study, presented at a meeting of sleep experts and researchers in Denver, showed that coffee stops affecting alertness, performance and mood after three nights of poor sleep.

Tracy Doty, a scientist at the Walter Reed Army Institute, said:

"Each night when we don't get enough sleep, we accumulate sleep deprivation, and the same amount of caffeine is no longer enough."

48 individuals included in the aforementioned institute's research slept only 5 hours per night for five consecutive days (the recommended length of sleep is between 7 and 9 hours per day). Half of the participants were given chewing gum with caffeine equivalent to two cups of coffee twice a day, and half were given a placebo. The first group, which consumed caffeine, saw a noticeable improvement in their mood and efficiency at work in the first days. But after three sleepless nights, the caffeine stopped working for them too. The level of caffeine's effect fell to that of the placebo group.

So we can't make up for sleep with anything. Sooner or later you have to get a good night's sleep.