Ahh, so now I understand why I can drink coffee all day and it doesn't seem to affect my sleep. ~ Ilene
Fifty college students were asked to record their caffeine consumption and their sleeping and waking times for a week. The students wore wrist devices that monitored their movements, to assess whether they had periods of wakefulness after they had fallen asleep. The researchers also measured caffeine levels in the students' saliva over the week.
As college students, they tended to be so sleep-deprived that, for most, "it didn't matter how much caffeine they had" they slept well whenever they finally hit the sack, said study researcher Jamie Zeitzer, an assistant professor of psychiatry and behavioral sciences at Stanford University.
However, for the early risers, the more caffeine in their bodies, the more time they spent awake during the night after initially falling asleep. This was not seen in the night owls.
The next step is to see whether this effect applies to people other than college students, Zeitzer said.
The amount of caffeine in a person at bedtime can vary widely, Zeitzer said. Some people's bodies clear caffeine within a few hours, but lunchtime coffee may still be in the system of other people even late at night…
The study was published online Feb. 13 in the journal Sleep Medicine.
Full article: Caffeine Disrupts Sleep for Morning People But Not Night Owls: Scientific American.
