Partying until the dawns, or snoring at 9:00 p.m.? This has been known to be a genetic trait, as various genes were found to impact your inner clock. But a new research shows that this inner clock is not only in your genes, but in each cell of your body!

A new study published in the "Proceedings of the National Academy of Sciences" reveals that skin cells can reveal the speed of a person's circadian clock. The biological clock controls sleeping, digestion, mental and physical performances along the 24 hours, and the hypothalamus, a brain center, was known to be in charge.

But the German-Swiss team led by Dr Steven Brown of the University of Zurich, based on lab-grown skin cells taken from 28 subjects, has shown that individual cells possess their own "clocks", whose function is determined by several clock genes.
The rhythm of the skin cells "clocks" was compared to the person's circadian type (early/"lark" or late/"owl") determined through questionnaires and it was a perfect match!

Some subjects suffered of Seasonal Affective Disorder (Sad), a type of winter depression affecting sleep patterns.
"The work could be used as a basis for the diagnosis of certain sleep disorders," said Dr. Simon Archer, Senior Lecturer in Molecular Neuroscience at the Surrey Sleep Research Centre, at the University of Surrey, Guildford; his team had detected a gene called Period3, whose mutation made its possessor a "lark".

The new research comes with a much more economic way of determining someone's circadian rhythm, as previous experiments involved keeping people in a lab for three days. This way, the subjects remain in contact with the external environment and sun light, and further researches could investigate peripheral clocks in tissues of the whole body, like heart, liver and gut.

"It now appears that virtually all cells in the body have their own ticking circadian clock, including skin cells. So, the skin cell assay is just a way of easily getting a handle on someone's body clock. But in more molecular detail than just knowing if they are a lark or an owl, which can be determined quite easily," said Archer.