Abstract
Light‐induced melatonin suppression in children is reported to be more sensitive to white light at night than that in adults; however, it is unclear whether it depends on spectral distribution of lighting. In this study, we investigated the effects of different color temperatures of LED lighting on children's melatonin secretion during the night. Twenty‐two healthy children (8.9 ± 2.2 years old) and 20 adults (41.7 ± 4.4 years old) participated in this study. A between‐subjects design with four combinations, including two age groups (adults and children) and the two color temperature conditions (3000 K and 6200 K), was used. The experiment was conducted for two consecutive nights. On the first night, saliva samples were collected every hour under a dim light condition (<30 lx). On the second night, the participants were exposed to either color temperature condition. Melatonin suppression in children was greater than that in adults at both 3000 K and 6200 K condition. The 6200 K condition resulted in greater melatonin suppression than did the 3000 K condition in children (P < 0.05) but not in adults. Subjective sleepiness in children exposed to 6200 K light was significantly lower than that in children exposed to 3000 K light. In children, blue‐enriched LED lighting has a greater impact on melatonin suppression and it inhibits the increase in sleepiness during night. Light with a low color temperature is recommended at night, particularly for children's sleep and circadian rhythm.
Highlights
Melatonin is an endogenous hormone secreted from the pineal gland in the brain, and its secretion is known to be related to the regulation of circadian rhythm and the sleep/wake cycle (Sack et al 2000; Cajochen et al 2003; Arendt 2005)
1998) as well as light intensity (Mcintyre et al 1989). In contrast to this possibility, we have recently found that nocturnal melatonin suppression in children is greater than that in adults in response to identical light conditions (Higuchi et al 2014): the percentage of melatonin suppression in children was approximately two-times greater than that in adults
As the graphs for individual melatonin change show, melatonin secretion in children was clearly suppressed by the light exposure regardless of color temperature
Summary
Melatonin is an endogenous hormone secreted from the pineal gland in the brain, and its secretion is known to be related to the regulation of circadian rhythm and the sleep/wake cycle (Sack et al 2000; Cajochen et al 2003; Arendt 2005). The suprachiasmatic nucleus (SCN), the circadian pacemaker, reduces melatonin production by the pineal gland during daylight hours and induces the release of melatonin at night. A causal relationship between pineal melatonin and health risks has not been revealed yet, light-induced melatonin suppression at night has been considered to be a possible factor causing several health risks in human The Physiological Society and the American Physiological Society.
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