A late-afternoon coffee may disrupt sleep more than expected. On alternate days, 12 volunteers with no sleeping problems were given 400 milligrams of caffeine (about the amount in a 20-ounce coffee from Starbucks) or a placebo pill six hours before bedtime. Caffeine not only doubled the time it took to fall asleep but also increased nighttime awakenings—resulting in an average loss of more than an hour of sleep over the night. Surprisingly, having caffeine at 5 p.m. was just as detrimental as consuming it right before bedtime, says Christopher Drake of the senior bioscientific staff at Henry Ford Hospital in Detroit. The half-life of the drug is five to seven hours, meaning that most people can clear only about half the caffeine in their systems in six hours, he explains. So if you want caffeine late in the day, less is better, and the further from bedtime, the better, he advises. Although the study didn't determine a minimal dose that can be consumed without impacting sleep, a cup of tea generally contains less caffeine than coffee (about 25 to 60 milligrams versus at least 100 milligrams).