‘Nine-to-five’ may have health risks, study finds

From age 10-55 people’s body clocks shift three hours later than traditional schedule

Teenagers aren’t lazy, just exhausted, according to a new study.

Current school and university start times are damaging the learning and health of students, said researchers from the University of Oxford, Harvard Medical School and the University of Nevada.

"At 10 years of age you get up and go to sleep in a way that fits the Dolly Parton 'nine-to-five' world that we live in, but this changes dramatically in adolescence, with a shift in body clocks to on average three hours later than these times," explained Paul Kelley, a researcher at Oxford university.

This means traditional school and university times leave teenagers chronically sleep-deprived by about 10 hours per week because their body systems are just not programmed to fit into those times, he said.


“After age 55, you go back to waking up earlier and sleeping earlier, but for those years in between, there are significant long-term health risks as well as poor performance and poor quality of life.”

The study looked at internal body clocks of different age groups and found that our ability to work effectively during traditional working hours changes dramatically at different ages.

The results show that at 18, young people should ideally start school or study at 11am, to coincide with their natural body clock, while children aged 16 should start school at 10am.

Inbuilt system

Our optimum hours of work and learning are determined by an inflexible, inbuilt system, he said. Researchers examined the genes responsible for regulating this rhythm.

“We cannot change our 24-hour rhythms, so in fact we cannot learn to become morning people.”

Our internal body clock, also known as the circadian rhythm, is a complex 24-hour cycle that affects all body systems, such as alertness, liver and kidney metabolism, and emotion.

“It’s distinct from the sleep-wake cycle and what we’ve discovered is that it cannot be manipulated like the sleep-wake cycle, but it naturally changes as we age”, explained Dr Kelley.

"The science explicitly shows that many people are suffering unnecessarily because of our work and study start times. There's no real rationale for start times for schools so there's a huge opportunity here to improve quality of life by putting these scientific findings into practice," he said at the British Science Festival in Bradford.

“We’ve joined together different types of scientists to study this and found that just one week with less than six hours of sleep [a night] leads to over 700 changes in how genes work in your body but with a full night’s sleep there were no changes.

“We know from studies of junior doctors’ working hours that sleep deprivation is associated with poor performance, with an up to 300 per cent increase in fatal consequences from one 24-hour shift per week in Harvard Medical School,” he said.

In Ireland, doctors have campaigned for several years to limit working hours to a maximum shift of 24 hours.