Cells belonging to habitual larks had the shortest glowing periods, while those of the night owls were the longest, the study found.
Brown likens the effect seen in late risers to that of someone keeping time with a slow wristwatch. "You end up being late for everything," he said.
"Now imagine your watch was fast, meaning that it had a time period of less than 24 hours. Then you'd be early for everything," Brown added.
The study reveals that genes, not just environmental factors such as day length, have a major influence on our circadian clock, he said.
(Related news: "Early Risers Have Mutated Gene, Study Says" [March 30, 2005].)
Russell Foster of the Nuffield Laboratory of Ophthalmology at the University of Oxford, England, was not involved in the research.
"Knowing that skin clocks 'tick' in the same way as brain clocks provides a nice tool to address whether a person is likely to be an early or late riser," Foster said.
"It's remarkable that measures from the skin can allow a prediction of brain-driven behavior."
"Human daily body rhythms are a complex, brain-related phenomenon," Brown said, "but it's directed by the same molecules that are present in your skin."
These cells give an accurate picture of an individuals daily body clock by mirroring the molecular workings of the central clock in your brain, the lead researcher said.
"By looking at slave clocks in the skin, we can get a better understanding of the way the [master] clock in the brain is working."
The research may lead to new treatments for people suffering from sleep disorders, the researchers said.
"Such treatments could potentially be used to reset a patient's 24-hour cycle to more sociable hours, so they wouldn't find themselves awake watching TV in the wee hours."
This would probably be done with drugs that target the circadian clock pathway, Brown said.
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