Being a night owl may be bad for your health but exposure to daylight can turn you into an early bird.
“Your chronotype is how early or late you are compared with everyone else,” says Céline Vetter, a circadian sleep specialist from the University of Colorado Boulder. “In modern societies, there is quite a spread. We’ve created an environment that is very different to the one our circadian system evolved with. We spend most of our days inside, so have low exposure to light during the day, and then we lighten up our nights.”
There is evidence that chronotype can influence health. Night owls have higher rates of obesity, high blood pressure and cardiovascular disease, for instance, as well as a greater chance of suffering depression than early birds.
Vetter’s most recent research looked at data from an ongoing US project, the Nurses’ Health Study II. She followed more than 32,000 middle-aged women who were depression-free at baseline, in 2009, to see whether they were diagnosed with depression or experienced symptoms. After accounting for other possible modifying factors, Vetter found the early birds had a 12-27% lower risk of depression compared with those who identified as intermediate types. Meanwhile, night owls had a 6% higher risk than the intermediates.
Although those numbers aren’t huge, Vetter believes they are significant from a prevention perspective.
“Some rare people are extremely early or late – that is a familial genetic condition – but most of us can adapt,” she says. “You travel across time zones and adapt, for instance.”
Any change may need to be gradual, so the way to become an earlier riser is to advance the alarm clock a little over a period of several weeks. And your natural chronotype may be stubborn at first.
“But being an early type seems to be beneficial, and you can influence how early you are,” says Vetter. “Light is the first thing. It is the most powerful signal to our circadian clock, so shifting your light exposure profile will help you shift your bedtime.”
Her advice is to take opportunities to be in natural light during the day by, for example, walking to work and going outside at lunchtime. Then, at night, dim the lights.
Also, limit screen time before sleeping. The light from electronic devices has been shown to delay the body clock, particularly when people have had little light exposure during the day.
Children are especially sensitive to light – their eyes let in more of it. So even short exposure to bright light at bedtime will suppress the sleep-promoting hormone melatonin and turn kids into night owls, which might have implications for their health later on.
Our chronotype tends to alter as we age – adolescents typically become later, and then earlier again as they mature. Gender also plays a role; on average, women are earlier than men.
US clinical psychologist Michael Breus, author of The Power of When, has identified four distinct chronotypes. He says dolphins are naturally light sleepers and tend to wake easily. Lions wake early. Wolves stay up later. Bears are in the middle of the spectrum. Breus advocates working with your chronotype for better sleep at night and more energy during the day.
Dramatically working against your biological clock will affect your health over time, altering glucose metabolism and the immune system. Shift workers are one of Vetter’s major research areas and she is interested in how we can design their schedules with individual-level strategies to help them stay well.
As for those shut indoors working for hours every day, light designers are becoming increasingly aware of the effect on well-being and are developing ways to improve things, making indoor light mimic the outdoors.
“Light changes throughout the day and across the seasons in colour and intensity,” says Vetter. “Now there are more and more systems that bring us closer to that.”
This article was first published in the October 13, 2018 issue of the New Zealand Listener.