Evening caffeine consumption ‘disrupts human circadian clock’

An international study has offered the first evidence that evening caffeine consumption can cause delays to the internal circadian clock.

Conducted by the University of Colorado at Boulder and the Medical Research Council's Laboratory of Molecular Biology in Cambridge, the study showed the amount of caffeine in a double espresso three hours before bedtime induces a 40-minute phase delay in the 24-hour human biological clock.

The magnitude of delay from the caffeine dose was about half that of the delay induced in test subjects by a three-hour exposure to a bright overhead light that began at each person's normal bedtime.

Bright light alone and bright light combined with caffeine induced circadian phase delays in the test subjects of about 85 minutes and 105 minutes respectively.

Study co-leader Professor Kenneth Wright said: "This is the first study to show that caffeine, the mostly widely used psychoactive drug in the world, has an influence on the human circadian clock."

The results could have implications for the treatment of some circadian sleep-wake disorders, as well as suggesting caffeine could be used as a means of addressing jet lag.