Even a brief exposure to light before bedtime might cause a preschooler’s sleep to be disrupted.
According to new CU Boulder research, even minor exposure to light might cause the essential sleep-promoting hormone melatonin to drop in preschoolers in the hour before bedtime, potentially disturbing slumber long after the light goes out.
The study, which was published last month, is the latest in a series financed by the National Institutes of Health that looks at how young children’s internal body clocks are different. It suggests that preschoolers are particularly vulnerable to the physiological effects of light at night, with some children being even more so.
First author Lauren Hartstein, a postdoctoral scholar in the Sleep and Development Lab at CU Boulder, said, «Our earlier study revealed that one pretty high intensity of bright light before night dampens melatonin levels by roughly 90% in young infants.» «We were astonished to observe substantial melatonin suppression across all light levels, even modest ones, in this investigation.»
Light is the body’s most powerful timekeeper.
The primary time cue for the body is light, which influences circadian rhythms, which control everything from when we feel sleepy or hungry to our body temperature throughout the day.
When light strikes the retina, a signal is sent to the suprachiasmatic nucleus, a portion of the brain that regulates body rhythms, including the creation of melatonin at night. When this exposure occurs in the evening, when melatonin levels are normally rising, it might inhibit or stop the body’s capacity to transition into biological nighttime.
Because children’s pupils are larger and their lenses are more translucent than adults’, light enters their eyes more freely. (According to one recent study, the transmission of blue light through a 9-year-eye old’s is 1.2 times that of an adult’s.)
«Kids aren’t simply small grownups,» said senior author Monique LeBourgeois, an associate professor of Integrative Physiology and one of the few scientists studying the circadian biology of young children around the globe. «This increased sensitivity to light may render them more vulnerable to sleep and circadian system disruption.»
In a ‘cave,’ you can do research.
For a new study, the researchers partnered with Colorado School of Mines mathematician Cecilia Diniz Behn to evaluate how vulnerable they are.
They recruited 36 healthy toddlers ranging in age from 3 to 5 years old to participate in a nine-day study in which they wore a wrist monitor to track their sleep and light exposure.
Parents put their children on a consistent sleep schedule for seven days in order to reset their body clocks and get them into a rhythm where their melatonin levels rose at roughly the same time each evening.
On the seventh day, researchers turned the children’s home into a «cave» by covering the windows with black plastic dimming the lighting, and taking saliva samples every half hour from early afternoon to after night. The scientists were able to establish a baseline for when the children’s biological night began and what their melatonin levels were as a result of this.
The young study participants were encouraged to play games on a light table an hour before a night on the last day of the trial, in a position comparable to that of someone looking at a bright phone or tablet. The intensity of the light varied between children, ranging from 5 to 5,000 lux. (A lux is defined as the light emitted by a candle held at a distance of one meter, or roughly three feet.)
Melatonin was reduced ranging from 70% to 100% following light exposure as compared to the prior night with minimal light. Surprisingly, the researchers discovered little to no link between the brightness of the light and the amount of sleep hormone that was released. This intensity-dependent reaction has been well-documented in adults.
Melatonin levels dropped by 78 percent in reaction to light measured at 5 to 40 lux, which is substantially lower than usual room light. Melatonin did not rebound in most youngsters tested even after the light was turned off for 50 minutes.
«Together, our data show that exposure to light before night, even at modest intensities, leads in substantial and lasting melatonin suppression in preschool-aged children,» stated Hartstein.
What can parents do?
This does not imply that parents should turn off the nightlight and leave their children in complete darkness before bedtime. However, at a time when half of the youngsters use screen media before bed, the study serves as a warning to all parents to turn off the gadgets and keep light to a minimum in order to help their children develop appropriate sleep patterns. In a dark room, a tablet at full brightness held 1 foot away from the eyes can measure up to 100 lux.
What if your child already has sleep issues?
«They may be more susceptible to light than other children,» LeBourgeois said, adding that light sensitivity is influenced by heredity as well as daytime light exposure. «In that situation, it’s even more critical for parents to monitor their children’s exposure to nighttime light.»