How caffeine disrupts your sleep

New research looks into the specifics of how late-in-the-day caffeine can disrupt your sleep at night.

You hear it all the time when it comes to sleep: Don't drink caffeine too late in the day. It's among the most common sleep tips -- and it's a good one. Caffeine, with its stimulant effects, is disruptive to good sleep. And these days, with the popularity of energy drinks and other caffeine-laden beverages and snacks, it's not difficult to wind up consuming caffeine throughout the day, even if you've set your coffee cup aside. The negative health consequences of too much caffeine also extend beyond sleep problems. Research shows that caffeine may contribute to cardiovascular problems. A recent large-scale study also suggeststhat heavy caffeine consumption -- more than four 8-ounce cups of coffee per day on a daily basis -- is linked to higher mortality rates in men and women.

But how late in the day is too late in the day to be consuming caffeine? Despite consensus about caffeine's sleep-disrupting effects, recommendations about the timing of caffeine consumption -- and when it's best to stop for the day -- can vary widely. Though an abundance of research has been conducted to establish caffeine's negative effects on sleep, very little attention has been paid to the specific timing of caffeine consumption relative to bedtime.

A new study attempts to fill in some of these important specifics about the effects of late-afternoon and early-evening caffeine consumption on nightly sleep. Researchers at Michigan's Henry Ford Hospital's Sleep Disorders & Research Center and Wayne State College of Medicine analyzed the sleep-disruptive effects of caffeine consumption at different lengths of time before bedtime. They found that caffeine consumed even six hours before bedtime resulted in significantly diminished sleep quality and sleep quantity. This is believed to be the first study to investigate directly the effects of caffeine at specific times before nightly sleep.

The study included 12 adult men and women, all of whom were healthy and were normal sleepers who in their regular lives were moderate consumers of caffeine. During the study period volunteers kept up their normal sleep routines, which included bedtimes between 9 p.m. and 1 a.m. and wake times between 6 a.m. and 9 a.m. Participants' total nightly sleep duration fell somewhere in the range of 6.5 to 9 hours per night, with no regular habit of napping during the day. Throughout the study researchers tracked sleep by having participants keep sleep diaries and by using at-home sleep monitors. Participants were given doses of caffeine in pill form as well as placebo pills, on a schedule that enabled researchers to measure the sleep-disruptive effects of caffeine taken at three different points: at bedtime, three hours before bedtime, and six hours before bed. They found significant disruptions to sleep as a result of caffeine taken at all three points:

• Caffeine consumed zero, three, and six hours before bedtime significantly reduced total sleep time. Even caffeine consumed six hours before bed reduced total nightly sleep amounts by more than one hour.
• Caffeine consumed at all three points diminished sleep quality. Caffeine taken three and six hours before bedtime, as well as caffeine consumed at bedtime, significantly increased the amount of time spent awake during the night.
• Disruptions to sleep as a result of caffeine were perceived by volunteers (as recorded in sleep diaries) for caffeine consumed at bedtime and three hours before bed, but were not reported for caffeine taken six hours before bed. However, sleep monitors measuring total sleep time, and sleep efficiency (time spent sleeping relative to total time spent in bed) showed that caffeine consumed six hours before bedtime had significant detrimental effects to both.

This last finding is especially important, because it suggests that people can't -- and shouldn't -- rely entirely on their own perceptions of how much or little caffeine affects their sleep, especially caffeine consumed in the afternoon. Even if you don't feel that late-afternoon cup of coffee has a negative impact on your sleep, this study suggests that it is likely to be interfering nonetheless. This is one reason that I have long recommended a 2 p.m. cut off time for caffeine consumption.

Remember, limiting caffeine doesn't mean removing it entirely from your daily routine. A moderate amount of caffeine, consumed at the right times, can be useful and evenhealthful, stimulating alertness and energy. These new findings provide us with some really important specifics about just how significantly late-in-the-day caffeine can undermine a good night's sleep. Want to enjoy your coffee without wrecking your sleep? Follow these basic suggestions for consuming caffeine in a sleep-friendly way:

Stick to a 2 o'clock cut off. As this current study shows, late-afternoon caffeine can cause problems for your sleep, even if you aren't aware of it. To avoid sleep disruption, restrict your caffeine consumption primarily to the morning hours. If you do have a midday cup of coffee, make sure to drink it before 2 p.m.

Taper caffeine as the day progresses. Start your day with your most highly caffeinated beverage and ease up on the caffeine as the morning goes on. First thing in the morning is likely when you'll crave caffeine the most, and when it can do you the most good in terms of boosting energy and shaking off the effects of a night's sleep. Switch over to tea or decaffeinated coffee as the morning continues, to keep overall daily caffeine amounts moderate and be comfortably caffeine-free by mid-afternoon.

Avoid jumbo drinks. These days, everything seems to be "super-sized" -- and caffeinated drinks are no exception. From a 20-plus-ounce latte or soda to a caffeine-packed energy drink, a lot of caffeine products deliver way more of the stimulant than is healthful. Stick to something much closer to the old-fashioned 8-ounce cup, and savor it.

Don't ignore your sleep problems. Being tired makes us more likely to feel the need for caffeine, and that extra consumption can in turn make sleep problems worse. Avoid this sleep-disruptive cycle by making sleep a daily priority. Practice good sleep hygiene and talk to your doctor about how you are sleeping, particularly about any problems that arise.

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