Scientists have identified the mechanism that controls the internal 24-hour clock of all forms of life -- from us to algae.
Researchers from Britain's Cambridge and Edinburgh universities, whose work was published in the journal Nature on Wednesday, said their findings provide important insight into health-related problems linked to people such as nurses, pilots and other shift workers, whose body clocks are disrupted.
The studies also suggest that the 24-hour circadian clock found in human cells is the same as that found in algae, and dates back millions of years to early life on earth, they said.
In the first study, Cambridge scientists found for the first time that red blood cells have a 24-hour rhythm.
This is significant, they explained, because circadian rhythms have always been assumed to be linked to DNA and gene activity -- but, unlike most other cells in the body, red blood cells do not have DNA.
"The implications of this for health are manifold. We already know that disrupted clocks...are associated with metabolic disorders such as diabetes, mental health problems and even cancer," said Akhilesh Reddy, who led the study. "By furthering our knowledge of how the 24-hour clock in cells works, we hope that the links...will be made clearer."
Many scientific studies have found links between working irregular hours and a greater likelihood of developing diabetes, heart disease and obesity. Sleep disruption is also associated with mental illnesses such as depression and bipolar disorder.
A team of scientists said last year they had used experimental drugs being developed by Pfizer to reset body clocks of mice in a lab -- opening up the possibility that drugs might in future be developed to restore rhythms to people whose body clocks have been messed up.
In these new studies, Reddy's team incubated purified red blood cells from healthy volunteers in the dark and at body temperature and sampled them regularly over several days.
They then examined the levels of certain biochemical markers -- proteins called peroxiredoxins that are found in virtually all known organisms and are produced in high levels in blood. The results showed that there was a modification in these proteins in a pattern that went back and forth over 24 hours.
A further study found a similar 24-hour cycle in marine algae -- suggesting that internal body clocks have always been important, even for ancient forms of life.
The researchers found those rhythms by sampling the peroxiredoxins in algae at regular intervals over several days. When the algae were kept in darkness, their DNA was no longer active, but the algae kept their circadian clocks ticking even without active genes.
Scientists had previously thought the circadian clock was driven by gene activity, but both the algae and the red blood cells kept time without it.
Andrew Millar of Edinburgh University, who led the second study, said it showed that body clocks are ancient mechanisms that have been around through a billion years of evolution.
"They must be far more important and sophisticated than we previously realized," he said. He added that more research was now needed to determine how and why these clocks developed in people, and what role they play in controlling our bodies.