Are you drinking coffee so much?

An after-dinner espresso may taste great, but it can keep you up. Drinking the equivalent of a double espresso 3 hours before bedtime shifts the clock back by an average of 40 minutes.Although caffeine’s effects on alertness and sleep are well known, researchers weren't sure how it affects the circadian clock in humans. The researchers also found that human cells in the lab exposed to caffeine lengthened their circadian clocks, an effect that the researchers linked to molecules known to play a role in cells’ 24-hour rhythms. The work also suggests that drinking coffee at the right time can help people adjust more quickly to jet lag, which is due to the body’s clock being out of sync with the local time zone.   Other research has shown that caffeine affects the circadian clock in animals such as fruit flies.