" Most people take a huge jolt of coffee in the morning to jumpstart their day-they get the super grande latte from Starbucks," said Charles Czeisler, who was recently appointed the Frank Baldino Jr. PhD professor of sleep medicine at Harvard Medical School. "Their caffeine levels soar only to fall as the day progresses in the face of rising sleepiness. They might be better off taking much smaller more frequent doses of caffeine, equivalent to a quarter of a cup of coffee, as the day wears on."
Though many studies have measured caffeine's sleep-averting effects, most do not take into account that sleep is governed by two opposing but interacting processes. The circadian system promotes sleep rhythmically-an internal clock releases melatonin and other hormones in a cyclical fashion. In contrast, the homeostatic system drives sleep appetitively-it builds the longer one is awake. If the two drives worked together, the drive for sleep would be overwhelming. As it turns out, they oppose one another.
Czeisler, who also leads the Division of Sleep Medicine at HMS, and his colleagues had reason to suspect that caffeine might be working to blunt the homeostatic system. For one thing, caffeine is thought to block the receptor for adenosine, a critical chemical messenger involved in the homeostatic dri
Contact: Judith Montminy or Misia Landau
Harvard Medical School