In the spring, later sunset and extended daylight exposure delay bedtimes in teenagers, according to researchers at Rensselaer Polytechnic Institute’s Lighting Research Center (LRC).
"Biologically, this increased exposure to early evening light in the spring delays the onset of nocturnal melatonin, a hormone that indicates to the body when it’s nighttime," explains Mariana Figueiro, PhD, associate professor. "This extended exposure adds to the difficulties teens have falling asleep at a reasonable hour."
Over time, when coupled with having to rise early for school, this delay in sleep onset may lead to teen sleep deprivation and mood changes, and increase risk of obesity and perhaps under-performance in school, according to Figueiro.
"This is a double-barreled problem for teenagers and their parents," says Figueiro. "In addition to the exposure to more evening daylight, many teens also contend with not getting enough morning light to stimulate the body’s biological system, also delaying teens’ bedtimes."
The new findings detailing the impact of early evening light in spring on melatonin onset and sleep times were published in Chronobiology International by Figueiro and LRC Director Mark Rea, PhD. The study found that 16 eighth-grade students from Algonquin Middle School in upstate New York experienced a delay in melatonin onset by an average of 20 minutes measured in 1 day in spring relative to 1 day in winter. Melatonin levels normally start rising 2 to 3 hours prior to a person falling asleep. The students also kept sleep logs as part of the study, which collectively showed a 16-minute average delay in reported sleep onset and a 15-minute average reduction in reported sleep duration measured in 1 day in spring relative to 1 day in winter.