After-dinner espressos are becoming more of a tradition – we have the Italians to thank for that – but to prepare for a good night’s sleep we are better off putting the brakes on caffeine consumption as early as 3 p.m. With a seven hour half-life, a cup of coffee containing 90 mg of caffeine taken at this hour could still leave 45 mg of caffeine in your nervous system at ten o’clock that evening. It is essential that, by the time you are ready to sleep, your body is rid of all traces.