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Pre-pubertal, mid-pubertal children more sensitive to evening light exposure
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Children in early to mid-puberty are prone to evening light sensitivity and suppressed melatonin levels, potentially leading to disrupted sleep patterns after repeated evening light exposure, according to research in The Journal of Clinical Endocrinology & Metabolism.
“Our group has provided evidence of biological processes that make it challenging for teens to get enough sleep and then to be rested for school when they need to get up so early,” Mary Carskadon, PhD, a professor of psychiatry and human behavior at Brown University, told Endocrine Today. “The phenomenon is called a phase delay and has its roots in the circadian timing system. Melatonin suppression, as tested in this new study, is linked to light's effects on this circadian system.”
Mary Carskadon
Carskadon, Stephanie J. Crowley, PhD, of the biological rhythms research laboratory at Rush University Medical Center in Chicago, and colleagues at other institutions analyzed data from 68 children aged 9.1 to 15.9 years (38 boys) participating in an in-lab sleep study for four continuous nights. Researchers divided the children into groups according to Tanner pubertal status, with children in the pre-/mid-pubertal group and 29 in the late-/post-pubertal group. All children received 1 hour of light exposure — a baseline exposure of 0.1 lux followed by 15, 150 and 500 lux. Participants were assigned to receive either evening (23:00 to midnight) or morning (3:00 to 4:00) light exposure depending on their availability. Researchers sampled salivary melatonin every 30 minutes while participants were awake.
The pre-/mid-pubertal children showed greater melatonin suppression at all tested light levels in the evening when compared with the late-/post-pubertal group (P < .05). Average melatonin levels for the pre-/mid-pubertal group were 9.2 pg/mL at 15 lux, 26 pg/mL at 150 lux and 36.9 at 500 lux; average melatonin levels for the late-/post-pubertal group were -5.3 pg/mL at 15 lux, 12.5 pg/mL at 150 lux and 23.9 pg/mL at 500 lux.
Researchers found no significant differences between groups for melatonin suppression measured by area under the curve for any morning light conditions; they also found no statistically significant differences in melatonin suppression between boys and girls in response to any of the light conditions at any time (P > .05).
Researchers noted that there were no statistically significant differences in circadian timing between puberty groups for either evening or morning light exposures.
“Our results indicate that delayed circadian timing in older adolescents is not due to increased sensitivity to evening light,” the researchers wrote. “It is more likely, therefore, that older adolescents have more delayed timing due to an increase in light exposure, rather than an increase in light sensitivity.”
The finding that the pre-/mid-pubertal group showed greater melatonin suppression at 15 lux was “particularly striking,” according to researchers, since this light level does not typically produce melatonin suppression in adults. Limiting light exposure for this age group in the evening and enhancing light exposure in the morning can counterbalance these effects, Carskadon said.
“Our findings show that even a very small amount of light in the evening suppressed melatonin levels in the middle-school-aged adolescents,” Carskadon said. “Because melatonin suppression by evening light is linked to a delay of circadian timing, the message is a that biologically driven later timing of sleep starts at this early age and needs to be considered when managing school and sleep schedules.” – by Regina Schaffer
Disclosure: One of the study authors reports being a shareholder and employee of Jazz Pharmaceuticals. Crowley and the other authors report no relevant financial disclosures.
Perspective
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Shahrad Taheri, MD, PhD, MBBS
Adolescence is a vulnerable period for both sleep loss and obesity. Shorter adolescent sleep duration has been associated with obesity and poorer school performance. As far as sleep is concerned, adolescents tend to go to sleep much later. This so-called phase delay has both a biological and social basis. The increased delay in adolescent bedtimes is biologically associated with pubertal stage. Adolescents tend to spend the evening interacting with their peers with increasingly available online social tools, and this also delays bedtimes. With school commitments, adolescence is associated with sleep loss because of later bedtimes combined with earlier wake times. Crowley and colleagues examined the sensitivity of the circadian system to evening light as measured through salivary melatonin levels. Suppression of melatonin levels is a measure of phase delay. They observed that early adolescents were more sensitive to the phase delaying effects of light exposure than late adolescents. Furthermore, even low-intensity light was associated with melatonin suppression. Thus, increased use of light-emitting technology, such as mobile telephones, in the evening in early adolescence may exaggerate phase delay resulting in later bedtimes, with downstream sleep loss, obesity and poorer school performance. Thus, reducing exposure to light through regulation of use of mobile devices in early adolescence could have benefits for both body weight and school performance.
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