Post-dinner coffee can lead to sleepless nights — not a surprise. A new study helps reveal why. Caffeine before bed distorts the master clock that tells the body what time it is. An evening dose of less caffeine than in a Starbucks tall medium roast delayed people’s clocks by about 40 minutes, scientists report September 16 in Science Translational Medicine.
Bodily clocks tick throughout the body, orchestrating the circadian rhythms that control everything from sleep to appetite to hormone levels (SN: 4/10/10, p. 22, SN: 7/25/15, p. 14). Caffeine taps directly into the master clock that syncs these far-flung timekeepers, Kenneth Wright of the University of Colorado Boulder and colleagues found. “This suggests that caffeine has a larger impact on us than we may have realized, from the circadian perspective,” he says.
The results have implications for the huge number of people who consume one of the world’s most popular stimulants, says pharmacologist and sleep researcher Hans Peter Landolt of the University of Zurich. Figuring out the details of how caffeine influences the body’s clocks might lead to better ways to prevent or treat sleep disorders, he says.
Over the course of about 49 days, five participants kept track of their sleep schedules at home for some of the days and nights, and came into the Sleep and Chronobiology Laboratory at UC Boulder for the others. During some of their lab stays, the participants were kept awake in rooms with low light and fed hourly snacks, a protocol that eliminated day and night signals. The hormone melatonin, which is plentiful at night and scarce during the day, served as a readout for circadian rhythms.
On some days, participants received caffeine three hours before their usual bedtime. The exact dose depended on body weight; a person weighing 152 pounds would get 200 milligrams of caffeine, about the amount in an 8-ounce cup of strong coffee. That dose shifted their circadian rhythms by about 40 minutes, melatonin levels revealed. The researchers didn’t test for changes in behaviors such as alertness or sleep shifts.
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CLOCKING IN After genetic tweaks, human cancer cells in a dish glow about once every 24 hours as a gene that encodes a timekeeping protein turns on. Scientists used these oscillations to study how caffeine influences cellular clocks.
Visual Aids, MRC LBM
Other experiments on cells in lab dishes help explain how caffeine influences cellular clocks. Caffeine changes the circadian rhythm by interfering with proteins that help detect the chemical messenger adenosine, which carries sleepy signals, the team found.
The results might help explain something researchers have noticed before: People who are night owls tend to drink more coffee. “It could be that the people who are having an after-dinner coffee are, unbeknownst to them, pushing their clock later and making them even later night owls than they would be otherwise,” Wright says.
Caffeine’s clock-shifting effects might also be harnessed for good. Used in a precise way, caffeine might turn out to be an important tool in regulating people’s sleep patterns, Wright says, helping to coordinate rhythms in people who do shift work or suffer from jet lag, for instance.
While the study is a good first step, there’s still much more to learn, says Landolt. Factors like age, genetics and culture can all influence how people respond to caffeine. More studies are needed to untangle how the stimulant influences people’s daily lives.