If you are an early bird or struggle to get out of the bed in the morning, then you should blame your genes for the habit.
A new study, led by Steven A. Brown of the Institute for Pharmacology and Toxicology at the University of Zurich, Switzerland, has discovered that a person's waking habits are mirrored by body cells that are equipped with their own daily alarm clocks.
Brown said that the finding represents the first internal look at the biological clocks of those suffering from sleeping disorders.
"One of the big surprises was that so much of our daily behavior was genetically encoded. The idea that skin cells are telling us anything about our behavior was, for me, quite fascinating," Brown said.
The study investigated the circadian rhythm, the brain-controlled phenomenon that governs various body functions over a 24-hour period, of extreme late and early risers.
In the study, the researchers recruited suitable volunteers using TV advertisements shown between 3 a.m. and 4 a.m.
"We got both our early types and our late types that way. Some had not yet gone to bed, while others were already up," Brown said.
Skin cells taken from the volunteers were cultured in the lab and injected with a bioluminescence gene found in fireflies.
These altered cells lit up or dimmed according to an individual's sleeping patterns. The study found that cells belonging to habitual larks glowed for the shortest period, while those of night owls glowed the longest.
"The study reveals that genes, not just environmental factors such as day length, have a major influence on our circadian clock. Human daily body rhythms are a complex, brain-related phenomenon, but it's directed by the same molecules that are present in your skin," Brown said.
"These cells give an accurate picture of an individual's daily body clock. The findings provide the first insight into the molecular workings of the central clock in your brain. 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," he added.
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," the authors said.
The study is published in the journal Proceedings of the National Academy of Sciences.