Caffeine is the most widely consumed psychoactive drug in the world. An estimated 85% of Americans drink one or more caffeinated beverages per day, with coffee as the main choice, followed by tea, sodas, and off-the-shelf energy drinks. Americans consume an average of 180 milligrams of caffeine daily—roughly the amount in two 8-ounce cups of coffee.
Coffee and other caffeinated drinks can provide some important benefits. Caffeine is a potent wake-up call in the morning and a pick-me-up later in the day. In some people, it enhances concentration and short-term memory. A recent review in Prehospital Emergency Care of caffeine’s effects on emergency medical personnel found that caffeine boosted alertness, agility, reaction time and coordination. And, of course, coffee and tea are centerpieces of social interactions in many cultures.
The benefits can come at a cost. Too much caffeine late in the day tends to disturb sleep. But even in people who go to sleep clinics for frequent insomnia, a surprising number of them don’t fully appreciate the effect of caffeine, even when it’s consumed fairly early in the day. What’s more, some research suggests that older adults may be more prone to the effects of daytime caffeine on sleep than younger people.
“You would think most people would be aware nowadays, but I would say a quarter to a third of patients we see with insomnia do not realize that their caffeine intake habits are affecting their sleep,” says Khalid Ismail, MD, a pulmonologist and director of the Center for Sleep Medicine at Tufts Medical Center.
Lingering Effects: Caffeine’s effect on sleep depends not only on how much you ingest, but when you do so. According to a new, comprehensive review of research on caffeine and sleep in Sleep Medicine Reviews, caffeine persists for a surprisingly long time in the body. According to one study, participants had brainwave patterns characteristic of shallower sleep up to 16 hours after ingesting the amount of caffeine in a double espresso—even though the level of caffeine detectable in their saliva had fallen to zero by the time they went to bed.
The implication of that study is clear for those struggling with insomnia. “For people who say they have trouble sleeping, we recommend no caffeine at all after lunch time,” Ismail says.
But for people without obvious sleep problems, it’s harder to make a general recommendation on what time of day to curtail caffeine. It peaks in the blood about 2 hours after ingestion on average. But the time it takes for the body to break down just half of that caffeine ranges from 3 to 7 hours.
The bottom line: It may be fine for some people to have an after-dinner caffeinated beverage—as long as they can still sleep restfully. “Some people have a shot of espresso at dinner and they sleep like babies,” Ismael says. “Others have a decaf tea with lunch and they can’t sleep that night.”
Sleep Quality Counts: Difficulty falling asleep is just one effect of caffeine. Controlled sleep studies, which carefully monitor the brain and body through the night, show that caffeine can trigger repeated nighttime “arousals,” in which a person briefly wakes up briefly without necessarily being fully conscious of having done so. Arousals fragment sleep, which means a person spends proportionately less time in the deeper, most restful stages of the natural sleep cycle. So even though total sleep time remains steady, the quality of that sleep may suffer. The results include grogginess, reduced mental sharpness and slower reaction times.
What Should You Do? Occasional insomnia is not necessarily a cause for concern, especially during stressful life periods like moving, starting a new job or illness in the family. But if you are having sleep problems more than once or twice a week, and it’s persisted for months, talk to your doctor, who may refer you to a sleep specialist, rather than immediately opting for over-the-counter sleep aids or prescription sleeping pills. In fact, prescription sleep aids “should only be used temporarily to get people through a period of change or adjustment,” Ismail says. “Most people with insomnia are helped without sleep medications.”
In the meantime, try the easiest things first—like avoiding caffeine earlier in the day to see if it improves your sleep. You can take other steps to institute better general sleep habits, or “sleep hygiene” (see page 1, TAKE CHARGE!). “Anyone can benefit from better sleep hygiene,” Ismail says.
But you don’t necessarily need to ban caffeine entirely. “If consumed in moderate amounts, caffeine can be very useful,” he says. “But don’t depend on it just to function, because that can lead to problems.”
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