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Afternoon caffeine associated with significant sleep disruptions, study shows

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You may want to reconsider that late afternoon trip to Starbucks.

A new study from the Journal of Clinical Sleep Medicine shows that consuming caffeine even six hours before bedtime can still cause significant sleep disruptions.

In a study conducted at Wayne State University in Detroit, Mich., researchers studied the way that caffeine exposure affected the sleep habits of 12 healthy sleepers.

Participants were given three pills a day and instructed to take one pill six hours before bedtime, one pill three hours before bedtime and one pill right before they went to sleep. Each day, only one of the pills contained 400 mg of caffeine, which is equivalent to the amount of caffeine found in two to three cups of coffee.  

Researchers then measured participants’ sleep using both subjective analyses and in-home sleep monitors that tracked their brain activity.  

Surprisingly, the researchers discovered that caffeine consumption appeared to cause significant sleep disruptions, regardless of when it was consumed during the day.

“We expected to see a time-sleep effect. We expected to see it at all time points, but we thought it would be more pronounced the closer to bedtime,” study author Thomas Roth, founder of the Sleep Disorders and Research Center at the Henry Ford Hospital in Detroit, told FoxNews.com. “(But) it was pretty comparable at all time points.”

In fact, consuming caffeine six hours before bedtime was associated with a one-hour reduction in total sleep time, the researchers reported.

“One hour of loss sleep – that’s huge.” Roth said. “The average sleeping pill you take will increase sleep for 30 minutes. This decreases sleep for about an hour. If you did this on a chronic basis, you’d become pretty sleep deprived.”

Though researchers didn’t examine why caffeine has such a pronounced effect on sleep, Roth suspects it has something to do with the way caffeine effects adenosine – a neurotransmitter that builds up in the brain during waking hours and decreases with sleep.

“Adenosine is what builds up in your brain to increase sleep pressure and (caffeine) may be negating that,” Roth said.

Overall, Roth said that chronic sleep deprivation can cause a number of ill health effects, including cognitive impairment during the day and negative mood.

Though heavy caffeine drinkers may be more immune to the stimulant’s effects, people who drink a moderate amount of coffee should avoid it later in the day.