Evening cup of coffee turns back body clock


Ever find yourself struggling to fall asleep after indulging in an after-dinner cup of coffee? The fact that caffeine interferes with sleep isn’t exactly a novel finding. However, researchers have now discovered the unique ways in which caffeine disrupts our circadian rhythm.

It turns out that consuming the equivalent of a double espresso three hours before bedtime actually turns back the body clock by almost one hour.

In a recent study, researchers from the University of Colorado examined five people who’d been living in a lab for 49 days. During this time, the participants had no access to external light or clocks.

Some of the subjects were then given the equivalent of a double espresso a few hours before bedtime. (The others were given a placebo.) They were also exposed to either dim or bright light. Why? Bright light has been shown to push back our circadian clocks.

When compared to participants who’d received a placebo, those who’d received caffeine were uniquely affected. Melatonin (a.k.a. the “sleep hormone”) was released 40 minutes later in this group.

Building on these findings, researchers from the Medical Research Council in the U.K. performed a similar experiment where they exposed human cells to caffeine in a lab setting. The result? It also appeared to delay the cells’ “built-in circadian rhythm.”

“The effect of caffeine on sleep and wakefulness has been long established, but its impact on the underlying body clock has remained unknown,” Dr. John O’Neill, joint lead researcher at the MRC Laboratory of Molecular Biology, said in an MRC press release. “These findings could have important implications for people with circadian sleep disorders, where their normal 24-hour body clock doesn’t work properly, or even help with getting over jet lag.”

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