Both Johnson and Katz find that caffeine affects sleep. Johnson avoids it altogether, while Katz avoids it after 4 p.m., at the latest, and usually doesn’t have any after 2 p.m.
Why it works: Caffeine affects people differently. If you find that you’re sensitive and it’s keeping you up at night, you’d do best to cut back or limit it to the morning only (and if you still are having trouble sleeping, try cutting it out altogether). Caffeine may also impair sleep more as you get older, according to research in Sleep Medicine. Remember that while coffee, tea and soda are big sources of caffeine, chocolate also delivers caffeine (an ounce of dark chocolate has about 25 mg of caffeine, equivalent to a quarter cup of brewed coffee).