Afternoon Caffeine Might Disrupt Sleep

Sleep disrupted by caffeine as early as six hours before bedtime

/ Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

(RxWiki News) Many people drink coffee in the afternoon for a quick jolt of energy at the end of their workday. But afternoon caffeine may be adding to sleep problems and tiredness throughout the day.

A recent study found that caffeine significantly disrupted sleep patterns, even when taken many hours before bedtime.

The researchers suggested that people stop using caffeine as early as six hours before going to sleep.

"Discuss your caffeine usage with a doctor."

The lead author of this study was Christopher Drake, PhD, FAASM, from the Sleep Disorders & Research Center of Henry Ford Hospital and the Department of Psychiatry and Behavioral Neurosciences at Wayne State College of Medicine in Detroit, Michigan.

The study included 12 people between the ages of 19 and 48. All of the participants had been physically examined and clinically interviewed and were confirmed to be healthy sleepers. There were six men and six women, and their average age was 29.44 years.

None of the participants had insomnia or any current or past histories of psychiatric or medical conditions.

Every participant reported sleeping between 6.5 and 9 hours per night on a regular basis, with an average period of 30 minutes to fall asleep. In addition, the participants reported having either three servings of caffeine per day or five servings of caffeine per week.

The researchers considered one serving of caffeine to be 100 mg. The participants consumed an average of 115 mg of caffeine per day.

The researchers instructed the participants to keep their normal sleep schedules for the first week of the study. They all had to go to sleep between 9:00 pm and 1:00 am and wake up between 6:00 am and 9:00 am, and were not allowed to nap during the day.

Then, each participant was given 400 mg of caffeine before their bedtime for four study days.

The study days alternated with days that participants were not given caffeine.

Each participant was given a pill at six hours before, three hours before and right at bedtime — one of them was a caffeine pill and the other two were placebos (fake pills). The participants did not know which pill was the caffeine pill.

The participants kept sleep diaries and wore monitors at night to track their sleeping patterns.

The findings showed that the average time spent sleeping each night decreased by 1.1 to 1.2 hours at all three of the caffeine times compared to the placebo.

The researchers also found that the caffeine given three hours before bedtime increased the time until a participant fell asleep by an average of 17.2 minutes compared to the placebo.

The findings also revealed that the amount of time the participants were awake during the night increased with each caffeine time, but the time for the bedtime caffeine was not statistically significant.

For caffeine six hours before bedtime, the wake time during sleep increased by eight minutes relative to the placebo, and for the caffeine three hours before bedtime, the wake time during sleep increased by 27.6 minutes.

The researchers concluded that taking 400 mg of caffeine six hours or less before bedtime can significantly disrupt sleeping time, length of time to get to sleep and time awake during the night.

They also believe that more research is needed with an older study population.

The authors noted a few limitations of their study.

First, the researchers did not have blood samples, so they did not definitively know to what extent each caffeine time affected sleep disturbance.

Second, the study population was very small. Third, the researchers allowed the participants to use caffeine during the day before 4:00 pm and that may have contributed to sleep disturbance.

Fourth, the equipment used to monitor sleep patterns was relatively new. Lastly, the study participants were relatively young, so the findings may not be applicable to the general population.

This study was published in the November edition of the Journal of Clinical Sleep Medicine.

Zeo Inc. provided funding.

Review Date: 
November 20, 2013
Last Updated:
November 25, 2013