A new scientific study shows that bright electric light exposure of preschool children in the evening suppresses melatonin production almost completely, an important addition to the growing body of research in this area. Melatonin suppression is a marker of disruption of our circadian rhythms.
Ten kids, ages 3 to 5, were exposed to bright light for one hour before their habitual bedtime, about 8 p.m. Melatonin suppression (where the body stops producing this hormone) began within 10 minutes and continued for another hour after the bright light was turned off at 8 p.m., which was well into their usual sleep period. Melatonin is a hormone that is important for healthy circadian rhythms and good sleep.
This could undoubtedly reduce sleep quality, but may also cause other serious problems in the longer term.
When seeing the light can be bad
The new study built upon a 2015 study of children and adolescents ages 9 to 16. It reported greater sensitivity to light exposure in the younger children compared to the older. That study used several different evening light levels in a laboratory setting that ranged from dim , to moderate, to bright and showed a dose response; the dim light suppressed melatonin about 9 percent; moderate light about 26 percent; and bright light about 37 percent in the younger children, less so in the older kids.
Although the researchers used fluorescent room lights in their study, the authors make a point of suggesting that since smartphone use is now common in children, even preschoolers, the circadian effects from their use could be considerable because they expose children to bright light close to the face.
There are at least three reasons that too much light during the evening could matter to the health of children, and all are terrible: depression, suicide and cancer.
Excess evening electric light is part of what I call “light pollution,” which is defined as “pollution of night by electric light, whether inside at home or outside in the neighborhood and city.” It is a rapidly growing problem in the modern world.
Light pollution at its most intimate – the smartphone
Jean Twenge studies mental health and social adjustment in young people, particularly those born after 1995. Her research has focused on smartphones. Twenge has found links between “new media” screen time (e.g., smartphones) and risk of depression and suicide in teenagers based on two large samples of young people in the U.S.
Twenge proposes as possible causes for her findings social isolation, sleep deprivation, or both. In another recent analysis, Twenge focused on sleep duration and concluded that “increased new media screen time may be involved in the recent increases (from 35 percent to 41 percent and from 37 percent to 43 percent) in short sleep among adolescents.”
Circadian disruption could be the underlying culprit. Bright light in the evening delays transition to nighttime physiology, which should begin at dusk. It thereby degrades sleep quality.
There is also evidence that circadian disruption can cause depression and other adverse mood changes.
Too much light at night early in life, even in utero
Early life, including in utero, is a particularly vulnerable period. The establishment of circadian rhythms begins early in gestation but is not fully established at birth, as any new parent becomes acutely aware.
For these reasons, research attention should be directed to the effects of ill-timed electric lighting on pregnant women, such as alterations in hormone production that could then affect fetal development. Scientists who study this also need to focus on developmental effects in young children and adolescents.
For example, it is unknown the extent to which night lights in the nursery alter the consolidation of circadian rhythmicity in infants, and whether toddlers exposed to highly lit evenings at home are at risk. I believe this is an urgent issue because adverse effects could launch a child on a lifetime trajectory of ill-health and early death.