Preschoolers Exposed to Nighttime Light Lack Melatonin


Source: University of Colorado at Boulder

Summary: Researchers in a new study found that exposing preschoolers to an hour of bright light before bedtime almost completely shuts down their production of the sleep-promoting hormone melatonin.


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. Use of electronic media among young children has tripled since 2011. A new study comes at a time when the use of electronics is rapidly expanding among this age group and adds to a growing body of evidence suggesting that because of structural differences in their eyes, children may be more vulnerable to the impact light has on sleep and the body clock. Researchers from the University of Colorado at Boulder found that exposing preschoolers to an hour of bright light before bedtime almost completely shuts down their production of the sleep-promoting hormonemelatonin and keeps it suppressed for at least 50 minutes after lights out. The study findings were published in the journal Physiological Reports.

Dim-light environment

CU Boulder researcher Lameese Akacem and undergraduate research assistant Allie Coy play with Lauren Meier over a light table in Meier’s Colorado home. Credit: University of Colorado Boulder

For the study, the researchers enrolled 10 healthy children ages 3  5 years in a seven-day protocol. On days one through five, the children followed a strict bedtime schedule to normalize their body clocks and settle into a pattern in which their melatonin levels began to go up at about the same time each evening. On day six, research team came into the children’s homes and created a dim-light environment, covering windows with black plastic and swapping out existing lights with low-wattage bulbs. This ensured that all the children were exposed to the same amount of light-which can influence melatonin timing and levels-before samples were taken. They found that Melatonin levels were 88% lower after bright light exposure. Levels remained suppressed at least 50 minutes after the light was shut off. Light is our brain clock’s primary timekeeper. This heightened sensitivity to light may make them even more susceptible to dysregulation of sleep and the circadian clock.

Assoc. Prof. Monique LeBourgeois “The preschool years are a very sensitive time of development during which use of digital media is growing more and more pervasive”, “We hope this research can help parents and clinicians make informed decisions on children’s light exposure.”

The takeaway for parents today: Dim the lights in the hours before bedtime.


More Information: Lameese D. Akacem et al, “Sensitivity of the circadian system to evening bright light in preschool-age children”, Physiological Reports (2018). DOI: 10.14814/phy2.13617 


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