Though researchers have widely examined the effects of bright screen exposure at nighttime on adults and adolescents, a new study from the University of Colorado Boulder has taken the first step in specifically looking at the impact it may have on preschoolers.

"Although the effects of light are well studied in adults, virtually nothing is known about how evening light exposure affects the physiology, health, and development of preschool-aged children," said lead author Dr. Lameese Akacem, a CU Boulder instructor and researcher in the Sleep and Development Lab. "In this study, we found that these kids were extremely sensitive to light."

Given the anatomical and structural difference in the eyes of children, they are more sensitive to light than other age groups. The new research studied the hormonal effects this could have on the quality of sleep among preschoolers. The study was focused on melatonin, a hormone responsible for inducing sleep and controlling the sleep and wake cycle. It also plays a role in other bodily processes, regulating temperature, blood pressure, and glucose metabolism.

The experiment involved a group of ten healthy children aged 3 to 5. The researchers had the children follow a regular sleep schedule for five days to establish a pattern for their body clocks to settle into. They also had their saliva checked several times in a day to measure the baseline levels of melatonin. On day six, the homes of the children were transformed into low-light “caves” with the windows covered with black plastic and swapped in low-wattage light bulbs.

The following evening, the children played with magnetic tiles on top of a light table emitting 1,000 lux of light for a period of one hour, after which the researchers collected samples once again. When compared to the night before, they found that melatonin levels had dropped drastically, nearly 88% lower after bright light exposure. The levels also remained suppressed for almost an hour after the lights were turned off as most of the children were not even get back to 50 percent of the melatonin levels seen the day before.

Limitations included the small sample size of participants and the use of light which was more intense than what is typically emitted from electronics.

Researchers noted that in a previous study, one hour of a light stimulus (which was 10 times more powerful than the one used in the current study) suppressed melatonin by only 39 percent in adults. The amount of melatonin secreted in the brain is influenced by exposure to light as Dr. Akacem explains that "the lens is a lot clearer" in the eyes of preschool children. "The pupils are larger, which allows more light to hit the retina and a stronger signal to the clock," she said.

Last year, a national survey revealed that the use of electronics by young children nearly tripled since 2013 due to the rise of easily accessible, handheld devices such as tablets and smartphones. "One important takeaway is that parents should avoid having children exposed to very bright light before bedtime," Dr. Akacem said.