Researchers have discovered that caffeine can delay normal sleep times by as much as 40 minutes, if consumed three hours before anticipated bedtime.
The amount of caffeine associated with sleep disruption was equivalent to what is typically in two shots of espresso. Kenneth Wright, head of the Sleep and Chronobiology Laboratory at the University of Colorado in Boulder, said some coffee shop brews typically contain more caffeine than that.
Scientists have known for a long time that caffeine disrupts chemicals in the brain that affect wakefulness and block chemicals that promote sleep.
“This particular finding tells us that the timing of sleep and wakefulness will be pushed later because of an effect on the clock, not just promoting wakefulness chemicals in the brain,” Wright said.
This is important because the natural process of circadian rhythm also affects hormone production and cell regeneration in the human body.
Not getting enough sleep can affect mood. It can also promote disorders like diabetes.
To look into caffeine’s effect on the circadian clock, researchers at the Colorado university and the Medical Research Council Laboratory of Molecular Biology in Cambridge, England, first noted the sleep-wake cycles of five healthy volunteers.
Over the course of a 49-day study, investigators gave the participants 200 milligrams of caffeine, the equivalent amount found in two shots of espresso, a few hours before bed and noted how long it took them to fall asleep.
The volunteers were also exposed at night to bright light, which is known to disrupt sleep.
Caffeine did more than bright light in interrupting the circadian clock, and therefore patterns of sleep.
The researchers also looked at the biological function of a sleep hormone and found caffeine interrupted a core component of sleep at the cellular level.
Wright said adjusting one’s biological clock in this way could also be beneficial.
“Another example of an implication of our findings is we may be able to use caffeine to help shift our clocks westward when we’re traveling across many time zones," he said. "In this case here, caffeine may help us adapt to jet lag must faster.“
The findings, published in the journal Science Translational Medicine, also suggest people who want to wake up earlier in the morning might consider giving up that nighttime cup of java.