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A study was published on March 4, 2018, “Sensitivity of the circadian system to evening bright light in preschool-age children.”  It quantifies the amount of evening light-induced melatonin suppression in children, specifically pre-school age, 3 to 5 years old. This study also built upon another study which was done in 2015 on pre-adolescent and adolescent children. The authors of this older study found that school-age children were nearly twice as sensitive to melatonin suppression than their parents. The authors of this current study wanted to look at how very young children, ages 3 to 5 where affected by bright light at bedtime.

What are circadian rhythms and why would they cause melatonin suppression in children?

The body makes and keeps its own circadian rhythms naturally. Because the body is attuned to other natural occurences, stuff in the environment affects the natural development of circadian rhythms in mammals and all other species on earth. More and more studies are finding that light (daylight) and dark (nighttime) affect human cycles or biorhythms. Our circadian rhythms may influence many parts of our lives, such as sleep and wake cycles, eating habits, digestion, hormone release, body temperature. Chronic health conditions like sleep disorders, diabetes, obesity, depression, bipolar disorder and SAD or seasonal affective disorder. Circadian rhythm and sleep are tied closely together. We have a ‘master clock,’ which is called in biological terms, the suprachiasmatic nucleus or SCN. The video below gives a terrific explanation of what it is and how it works in our bodies. Resource: National Institute of General Medical Sciences: Circadian Rhythms

What is the human suprachiasmatic nucleus?

In mammals, the regulating clock that results in a 24-hour rhythm is the suprachiasmatic nucleus (SCN), located in a part of the brain called the hypothalamus. In a nutshell, our eyes first synchronize to light. The light travels the optic nerve to the base of the brain at the hypothalamus. It is a little 2 winged structure, very tiny, with millions of neurons. These are actually “cellular clocks,” which means that the clock emerges from the cell.

Melatonin Suppression in Children – Study Findings & Discussion

This study addressed a gap in understanding about melatonin suppression in children younger than school-age. The authors knew from the findings of a 2015 study that melatonin was suppressed in school-age children nearly twice as much as their parents with moderately bright evening light, about 580 lux.

Our circadian clocks regulate melatonin production with the side effect of promoting good sleep. With approximately 30% of young children experiencing difficulties transition from sleep to wakefulness, this study helps people understand what might be the cause. The reason for this is that they’ve lost that 50 minutes of darkening light and so have trouble falling asleep once the lights are out.

Lighting Sources and Brightness

Typical indoor lighting is less than 200 lux. A lux is a unit that is used for measuring the amount of light falling on a surface and that is equal to one lumen per square meter. On the other hand, bright indoor lighting ranges from 300 to 1000 lux. The study used 1000 lux bright lights. However, light from electronic devices is about 30 to 50 lux, which seems very low and nothing to be concerned about. Light emitted from electronic devices is not even comparable to even bright indoor lighting. 

Melatonin Suppression in Children – More to Study

Electronic devices give off light in short wavelengths. Lens transparency changes across age group are most prominent at short wavelengths. Then is may make sense that the light from ever present electronic devices will have as detrimental effect as the findings from this study suggesting that melatonin suppression in children is much greater at younger ages.

For that reason, a study assessing the effect of media use right before sleep on melatonin levels, on circadian timing, and how they do affect sleep and alertness in early childhood.


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