ResearchGate: How does modern life affect our sleep patterns?
Ellen Stothard and Kenneth Wright: Because of the demands of our 24-hour society, people often sleep less during the week and try to catch up on sleep on weekends. Sleeping in late on weekends to “recover” from the work week reduces our exposure to bright light in the morning and increases electrical light exposure at night. Bright morning light exposure is important for synchronizing the timing of the biological clock to the world around us. Decreased morning light exposure can push back the internal biological clock over the weekend, which makes it challenging to go to bed on Sunday night and wake up early for work on Monday morning.
We also find that the internal clock is timed later in modern society, regardless of what happens on the weekend. This can make it more difficult to go to bed at a reasonable hour and be alert in the morning.
RG: How do these changes affect us?
Stothard and Wright: This mismatch in timing between the internal biological clock and the external world is called social jet lag. If the timing of the clock has been delayed over the course of the weekend, waking up at an earlier time on Monday could mean that you are waking up during your biological night, when your clock is promoting sleep and inactivity, not wakefulness and activity. This has been shown to lead to impaired cognitive and metabolic function.
RG: What did you look at in your study?
Stothard and Wright: We conducted two studies in which people living in a typical modern environment wore special watches on their wrists that measured sleep-wake activity and light exposure. They then came to the laboratory for a 24-hour visit. We sampled saliva hourly to assess the hormone melatonin. Low melatonin levels represent the biological day, and high levels represent the biological night. In the first study, we then took people camping for a week in the winter. In the second study, people either went camping for the weekend or stayed at home in a modern environment. We then reassessed the circadian melatonin rhythm after the week or weekend.
RG: What happens to people’s sleep patterns when they go camping?
Stothard and Wright: When camping in the winter, people are exposed to 13 times more light over the course of the day and to dim moon, star, and campfire light after sunset. This increase in light exposure during the day and decrease in light exposure at night shifts the timing of the internal clock earlier. In the winter, this causes the timing of the internal biological night to expand, and become longer. During the summer, camping leads biological and natural day-night cycles to become more closely synchronized, demonstrating that humans are responsive to seasonal changes in the natural light-dark cycle.
RG: Are there ways people who don’t like camping or don’t have time for it can approximate this effect?
Stothard and Wright: If people want to keep an earlier bedtime, it is important for them to keep as consistent an earlier schedule as possible, and to increase daytime exposure to sunlight. This could mean starting your day with a walk or sitting outdoors while having your morning coffee. They should also reduce nighttime exposure to electrical lighting at night, including lights in the home and personal electronic devices such as computers, TVs, and cell phones.
Our findings also highlight an opportunity for architectural design to bring more natural sunlight into the modern built environment and to work with lighting companies to incorporate “tunable” lighting that would be able to change across the day and night as occurs outside in the natural world.