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Drinking coffee before bed won’t wreck your sleep — but this will – MarketWatch

A late cup of coffee isn’t hurting your sleep nearly as much as a cigarette before bed.

So says a new study published in the journal Sleep, which analyzed data from 785 African American men and women. And while nicotine and alcohol use four hours before bedtime were both associated with worse sleep — even after controlling for factors like age, gender and BMI — caffeine was not.

African Americans have been underrepresented in research examining the effect of these substances on sleep, the reported noted, even though they are more likely to experience short sleep duration and fragmented sleep than non-Hispanic Whites, as well as worse health consequences associated with poor sleep (including cardiovascular disease, diabetes, hypertension and certain cancers) compared to other racial and ethnic groups. This study was intended to help close that research gap, lead author Dr. Christine Spadola from Florida Atlantic University told MarketWatch.

“There is no reason to think that these findings are not generalizable to other racial or ethnic groups,” she said. “This is one of the largest investigations of the impact of alcohol, caffeine and nicotine to date with more than 5,000 nights of data.”

Dr. Spadola (with collaborators from Harvard, Emory University, the University of Mississippi and Brigham and Women’s Hospital) worked with subjects who wore wrist-watch-like sensors that tracked the quality of their sleep for an average of 6.7 nights (adding up to 5,163 nights’ worth data). The subjects also kept sleep diaries where they logged whether or not they had any alcoholic drinks (like beer, wine or hard liquor), any drinks with caffeine (like coffee, tea or soda) and/or smoked in the four hours before they went to sleep, although they did not track how much of each substance they consumed.

An evening cigarette is worse for sleep than a late coffee, this study finds.

And good news for coffee and tea lovers: consuming caffeine in the hours before going to bed did not have any impact on how long it took the subjects to fall asleep, how long they slept, or whether they woke up during the night. Despite often repeated recommendations not to consume any caffeine in the hours before going to bed, caffeine affects different people in different ways. Some studies have also found that caffeine had no effect on sleep, or, the studies that did were limited by small sample sizes that weren’t racially diverse. A 2012 study also found that night owls weren’t as affected by caffeine in the evening as early birds.

As for those enjoying happy hour drinks after work or sipping wine with dinner, evening alcohol was linked with “a small but statistically significant reduction” in sleep efficiency (or the percentage of time spent asleep while in bed) and fragmented sleep. Research has shown that while most people think that a night cap helps them relax, booze is actually a snooze-killer. While it may appear to help people fall asleep faster initially, it reduces your body’s ability to go into deep sleep, so you wake up feeling unrested. Plus, alcohol drinkers get up in the middle of the night to use the bathroom more often because booze blocks the reabsorption of liquid in the body, which dehydrates you and fills your bladder more quickly at the same time.

Related: These are the three biggest sleep myths

But the biggest sleep wrecker in this study was nicotine, particularly among subjects with insomnia. The insomniacs who smoked within four hours before bed were associated with sleeping just over 42 minutes less, on average, compared to those with insomnia who didn’t smoke. Smokers without sleep issues also got up more frequently during the night (reporting six more minutes of wake after sleep onset, or WASO) and had lower sleep efficiency than non-smokers.

The researchers wrote that this stems from nicotine being a stimulant, as well as the body undergoing nicotine withdrawal while a person sleeps, which disrupts their rest. Previous research has also associated nicotine use with trouble falling asleep, lighter sleep, higher rates of obstructive sleep apnea and sleeping for a shorter length of time compared to those who don’t use it. And of course, tobacco use accounts for nearly 6 million deaths worldwide each year, according to the CDC, and is the leading cause of lung cancer.

Related: Smoking costs you more than $27,000 a year. Here’s your no B.S. guide to quitting for good.

The study did not ask for how many cigarettes, cups of coffee or alcohol servings that these men and women had each night, so more research is needed to assess how the dosage of each substance affects sleep. And some people with caffeine sensitivities may find that a late afternoon jolt of java does disrupt their sleep, so stick with what works for you.

More than a third of American adults get less than the recommended seven hours of sleep a night, according to the CDC. This costs the U.S. economy $411 billion a year in lost productivity, and Americans spent $41 billion on sleep aids in 2015, which is projected to hit $52 billion by next year.

For more tips on getting more fitful rest, these 4 sleep experts shared their own personal routines for catching Zs.

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