Drinking too much coffee may do more than simply keep you awake at night. Scientists report that caffeine delays the body's natural surge in the production of the sleep hormone melatonin.

That, in turn, disrupts the body’s biological clock — known as the circadian rhythm —that operates in every single cell in the body, allowing us to adapt to the external cycle of night and day, Medical News Today reports. 

The hormone melatonin, which makes people sleepy, is triggered by the dimming of the light.
Disruption of that clock —through shift work, jet lag, or sleep disorders — can lead to heart disease, Type 2 diabetes, Alzheimer's disease, and certain psychiatric conditions.

The new research, published in the journal Science Translational Medicine, found that drinking the equivalent of a double espresso three hours before going to sleep can turn back the body’s biological clock by an hour, by delaying a rise in the level of the hormone melatonin.

The finding, by scientists with the British Medical Research Council (MRC) Laboratory of Molecular Biology, has important implications treating sleep problems that strike more than 25 percent of Americans, according to the Centers for Disease Control and Prevention.

For the study, researchers monitored five people who spent 49 days in a lab without a clock or any knowledge of external light to tell them if it was night or day. Participants were exposed to bright or dim light and given either caffeine or an inactive placebo several hours before going to sleep. Their saliva was then tested later to see how much melatonin had been produced.

When caffeine was given, melatonin levels rose around 40 minutes later compared with the placebo. The researchers also added caffeine to human cells in a lab, and found that the built-in circadian clock was also delayed.

"These findings 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," Said lead researcher John O'Neill, M.D. He added that the findings, "right down to the level of individual cells," can help us understand how the natural 24-hour clock can be influenced, "for better or for worse."