It's no news to us that the caffeine in coffee can give you sleepless nights. But apparently that espresso has another way of deriving you of your sleep: it seriously delays your internal clock.
A study in Science Translation Medicine shows that a double espresso, consumed three hours before going to bed, considerably slows the generation of the sleep hormone melatonin, causing you to catch sleep less easily.
The study involved five people who were locked up in a sleep lab in the University of Colorado in Boulder for 50 days. When they received a dose of caffeine in the evening, their biorhythm slowed down by 40 minutes.
Dr. O'Neill, who executed the research, advises people not to drink coffee after 5 PM. Of course, this advisory time is later if you are a true nocturnal person. You should take care of your normal biorhythm.