Even dim light before bedtime may disrupt a preschooler's sleep
Broad range of intensity can sharply dampen sleep-promoting melatonin


Date:
January 27, 2022
Source:
University of Colorado at Boulder
Summary:
A new study of preschoolers finds that exposure to even very
low intensities of light before bedtime can sharply reduce
production of the sleep-promoting hormone melatonin, interfering
with sleep. It suggests that young children are highly susceptible
to the physiological impacts of light at night and some kids are
more sensitive than others.



FULL STORY ==========================================================================
Even slight exposure to light can prompt the critical sleep-promoting
hormone melatonin to plummet in preschoolers in the hour before bedtime, potentially disrupting slumber long after the light goes out, according
to new CU Boulder research.


==========================================================================
The study, published this month, is the latest in a series, funded by
the National Institutes of Health, examining how the central body clock
of young children is unique. It suggests that preschoolers are highly susceptible to the physiological impacts of light at night, and some
children may be even more sensitive than others.

"Our previous work showed that one, fairly high intensity of bright
light before bedtime dampens melatonin levels by about 90% in young
children," said first author Lauren Hartstein, a postdoctoral fellow in
the Sleep and Development Lab at CU Boulder. "With this study, we were
very surprised to find high melatonin suppression across all intensities
of light, even dim ones." Light: The body's strongest time cue Light is
the body's primary time cue, influencing circadian rhythms that regulate everything from when we feel tired or hungry to what our body temperature
is throughout the day.

When light hits the retina, a signal transmits to a part of the brain
called the suprachiasmatic nucleus, which coordinates rhythms throughout
the body, including nightly production of melatonin. If this exposure
happens in the evening as melatonin is naturally increasing, it can slow
or halt it, delaying the body's ability to transition into biological nighttime.



========================================================================== Because children's eyes have larger pupils and more transparent lenses
than adults, light streams into them more freely. (One recent study
showed that the transmission of blue light through a 9-year-old's eye
is 1.2-times higher than that of an adult).

"Kids are not just little adults," said senior author Monique LeBourgeois,
an associate professor of Integrative Physiology and one of the few
researchers in the world to study the circadian biology of young
children. "This heightened sensitivity to light may make them even
more susceptible to dysregulation of sleep and the circadian system."
Research in a "cave" To quantify how susceptible they are, the researchers collaborated with Colorado School of Mines mathematician Cecilia Diniz
Behn for a new study.

They enlisted 36 healthy children, ages 3 to 5 years, for a nine-day
protocol in which they wore a wrist monitor that tracked their sleep
and light exposure.

For seven days, parents kept the children on a stable sleep schedule
to normalize their body clocks and settle them into a pattern in which
their melatonin levels rose at about the same time each evening.



==========================================================================
On the eighth day, researchers transformed the children's home into what
they playfully described as a "cave" -- with black plastic on the windows
and lights dimmed -- and took saliva samples every half hour starting in
the early afternoon until after bedtime. This enabled the scientists to
get a baseline of when the children's biological night naturally began
and what their melatonin levels were.

On the last day of the study, the young study subjects were asked to play
games on a light table in the hour before bedtime, a posture similar to
a person looking at a glowing phone or tablet. Light intensity varied
between individual children, ranging from 5 lux to 5,000 lux. (One lux
is defined as the light from a candle 1 meter, or about 3 feet, away).

When compared to the previous night with minimal light, melatonin was suppressed anywhere from 70% to 99% after light exposure. Surprisingly,
the researchers found little-to-no relationship between how bright
the light was and how much the key sleep hormone fell. In adults, this intensity-dependent response has been well documented.

Even in response to light measured at 5 to 40 lux, which is much dimmer
than typical room light, melatonin fell an average of 78%. And even 50
minutes after the light extinguished, melatonin did not rebound in more
than half of children tested.

"Together, our findings indicate that in preschool-aged children,
exposure to light before bedtime, even at low intensities, results in
robust and sustained melatonin suppression," said Hartstein.

What parents can do This does not necessarily mean that parents must
throw away the nightlight and keep children in absolute darkness before bedtime. But at a time when half of children use screen media before
bed, the research serves as a reminder to all parents to shut off the
gadgets and keep light to a minimum to foster good sleep habits in their
kids. Notably, a tablet at full brightness held 1 foot from the eyes in
a dark room measures as much as 100 lux.

For those children who already have sleep problems? "They may be
more sensitive to light than other children," said LeBourgeois, noting
that genes -- along with daytime light exposure -- can influence light sensitivity. "In that case, it's even more important for parents to pay attention to their child's evening light exposure." special promotion Get
a free digital "Metabolism Myths" issue of New Scientist and discover the
7 things we always get wrong about diet and exercise. Claim_yours_now_>>> ========================================================================== Story Source: Materials provided by
University_of_Colorado_at_Boulder. Original written by Lisa
Marshall. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Lauren E. Hartstein, Cecilia Diniz Behn, Lameese D. Akacem,
Nora Stack,
Kenneth P. Wright, Monique K. LeBourgeois. High sensitivity
of melatonin suppression response to evening light in
preschool‐aged children.

Journal of Pineal Research, 2022; DOI: 10.1111/jpi.12780 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220127104208.htm

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