While there’s been a big push over the last handful of years to delay start times for high school, a group of researchers says it won’t help.
The research, conducted in the UK by the University of Surrey and Harvard Medical School predicts that turning down the lights in the evening would be much more effective at tackling sleep deprivation.
Teenagers like to sleep late and struggle to get up in time to go to school. The commonly accepted explanation for this is that adolescents’ biological brain clocks are delayed. It has been suggested that to remedy this, school start times should be delayed for older teenagers so that they are again in tune with their biological clock.
The study used a mathematical model that takes into account whether people are naturally more of a morning or evening person, the impact of natural and artificial light on the body clock and the typical time of an alarm clock, to predict the effects of delaying school start times.
The mathematical model showed that delaying school start times in the UK would not help reduce sleep deprivation. Just as when clocks go back in the autumn, most teenagers’ body clocks would drift even later in response to the later start time, and in a matter of weeks they would find it just as hard to get out of bed. The results did, however, lend some support to delaying school start in the US, where many schools start as early as 7am.
The mathematical explanation has its roots in the work of the 17th century Dutch mathematician Huygens. He saw that clocks can synchronise, but it depends on both the clocks and how they influence each other. From research over the last few decades we know that body clocks typically run a little slow, so they need to be regularly ‘corrected’ if they are to remain in sync with the 24-hour day. Historically, this correcting signal came from our interaction with the environmental light/dark ‘clock’.
The mathematical model shows that the problem for adolescents is that their light consumption behaviour interferes with the natural interaction with the environmental clock – getting up late in the morning results in adolescents keeping the lights on until later at night. Having the lights on late delays the biological clock, making it even harder to get up in the morning. The mathematics also suggests that the biological clocks of adolescents are particularly sensitive to the effects of light consumption.
The model suggests that an alternative remedy to moving school start times in the UK is exposure to bright light during the day, turning the lights down in the evening and off at night. For very early start times, as in some US regions, any benefit gained from delaying school start times could be lost unless it is coupled with strict limits on the amount of evening artificial light consumption.
The mathematical understanding of biological clocks suggests that adolescents are particularly sensitive to the effects of light consumption. However, the model can be applied to other age-groups as well. It can be used to design new interventions not only for sleepy teenagers but also for adults who suffer from delayed sleep phase disorders or people who are not synchronised to the 24-hour day at all.
The research draws attention to light, light consumption and darkness as important environmental and behavioural factors influencing health. This has implications for how we design the light environment at work and at home in our modern light-polluted societies.