The recommendations arise from a deeper understanding of circadian rhythms – our internal body clock, which determines optimum levels of concentration, wakefulness and work ability.
“At the age of 10 you get up and go to school and it fits in with our nine-to-five lifestyle,” Kelley said. “When you are about 55 you also settle into the same pattern. But in between it changes a huge amount and, depending on your age, you really need to be starting around three hours later, which is entirely natural.”
Ignoring our natural circadian rhythms could lead to exhaustion, frustration, anxiety, weight gain and hyper-tension, he said, and could make a person more prone to stimulant or alcohol use and risk-taking.