A new study shows that caffeine
consumption even six hours before bedtime can have significant, disruptive
effects on sleep.
"Sleep specialists have always
suspected that caffeine can disrupt sleep long after it is consumed," said
American Academy of Sleep Medicine President M. Safwan Badr, MD. "This
study provides objective evidence supporting the general recommendation that
avoiding caffeine in the late afternoon and at night is beneficial for
Results show that 400 mg of caffeine
(about 2-3 cups of coffee) taken at bedtime, three and even six hours prior to
bedtime significantly disrupts sleep.
Even when caffeine was consumed six hours
before going to bed, objectively measured total sleep time was dramatically
reduced (more than one hour). However, subjective reports suggest that
participants were unaware of this sleep disturbance.
The study is in the issue of the Journal
of Clinical Sleep Medicine, which is published by the American Academy of Sleep
"Drinking a big cup of coffee on the
way home from work can lead to negative effects on sleep just as if someone
were to consume caffeine closer to bedtime," said lead author Christopher
Drake, PhD, investigator at the Henry Ford Sleep Disorders and Research Centre
and associate professor of psychiatry and behavioural neurosciences at Wayne
State University in Detroit, Michigan.
"People tend to be less likely to detect
the disruptive effects of caffeine on sleep when taken in the afternoon,"
noted Drake, who also is on the board of directors of the Sleep Research
Drake and his research team studied 12
healthy normal sleepers, as determined by a physical examination and clinical
No caffeine after five
Participants were instructed to maintain
their normal sleep schedules. They were given three pills a day for four days,
taking one pill at six, three and zero hours prior to scheduled bedtime. One of
the pills contained 400 mg of caffeine, and the other two were a placebo.
On one of the four days, all three pills
were a placebo. Sleep disturbance was measured subjectively with a standard
sleep diary and objectively using an in-home sleep monitor.
According to the authors, this is the
first study to investigate the effects of a given dose of caffeine taken at
different times before sleep. The results suggest that caffeine generally
should be avoided after 5 p.m. in order to allow healthy sleep.