The experiment
To look into caffeine's effect on the circadian rhythm, or circadian clock, researchers first noted the sleep-wake cycles of five healthy volunteers.
The study lasted 49 days. Researchers gave the participants 200 milligrams of caffeine a few hours before bed. Two hundred milligrams of caffeine is about the amount found in two shots of espresso. Then the researchers noted how long it took the volunteers to fall asleep.
The volunteers were also exposed at night to bright light, which is also known to disrupt sleep. Caffeine, however, interrupted the circadian clock, and patterns of sleep, more so than bright light did. Caffeine affects the production of melatonin, the sleep-producing hormone.
When a person’s circadian rhythm is disrupted, sleeping and eating patterns are thrown off. A disrupted circadian rhythm increases the chance of heart disease, obesity and mental illnesses such as depression and bipolar disorder. Bipolar disorder is a disease of the brain where people experience extreme highs and extreme lows.
But caffeine’s effect on the body is not all bad.
Mr. Wright says people could use caffeine to help their body’s clock, for example, when they travel.
"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. In this case here, caffeine may help us adapt to jet lag much faster."
The scientists published their findings in the journal Science Translational Medicine. The scientists also give some common sense advice -- people who want to wake up earlier in the morning might want to avoid that nighttime cup of caffeine.
And that’s the Health & Lifestyle report.