“It’s like feet,” said Roenneberg. “Some people are born with big feet and some with small feet, but most people are somewhere in the middle.”

According to Roenneberg the problem is that our lives typically don’t take into account circadian rhythms as they might have when we spent more time outdoors in natural light. Many companies start the work day at 8am or 9am, putting their work schedules at odds with their employees’ body clock.

That mismatch, along with the pressure to be productive and be available to respond to email or take calls at all hours of the day and night, mean that many people suffer from what he calls “social jetlag”. In other words, their bodies are always in the wrong time zone. He estimates that more than 70% of people get up earlier than they should if the goal is to be well rested and perform their best.

When custom trumps biology

The mismatch between people’s internal clocks and the schedule they have to follow to get on in life starts in adolescence, said Paul Kelley at the University of Oxford’s Sleep and Circadian Neuroscience Institute in the UK. Kelley said that most people’s body clocks start moving forward around puberty. By the time they reach high school or secondary school, teenagers are getting up, on average, three hours earlier than they should because of early school start times in some cases as early as 7:30am. The result: chronic sleep deprivation, that hurts their ability to focus and could lead to longer term health problems like obesity and diabetes, he said. Because of a major public health push, some school districts in the US and the UK are moving school start times later.