Nocturnal Melatonin Suppression by Adolescents and Adults for Different Levels, Spectra, and Durations of Light Exposure

Abstract

The human circadian system is primarily regulated by the 24-h light-dark cycle incident on the retina, and nocturnal melatonin suppression is a primary outcome measure for characterizing the biological clock's response to those light exposures. A limited amount of data related to the combined effects of light level, spectrum, and exposure duration on nocturnal melatonin suppression has impeded the development of circadian-effective lighting recommendations and light-treatment methods. The study's primary goal was to measure nocturnal melatonin suppression for a wide range of light levels (40-1000 lux), 2 white light spectra (2700 K and 6500 K), and an extended range of nighttime light exposure durations (0.5-3.0 h). The study's second purpose was to examine whether differences existed between adolescents' and adults' circadian sensitivity to these lighting characteristics. The third purpose was to provide an estimate of the absolute threshold for light's impact on acute melatonin suppression. Eighteen adolescents (age range of 13-18 years) and 23 adults (age range of 24-55 years) participated in the study. Results showed significant main effects of light level, spectrum, and exposure duration on melatonin suppression. Moreover, the data also showed that the relative suppressing effect of light on melatonin diminishes with increasing exposure duration for both age groups and both spectra. The present results do not corroborate our hypothesis that adolescents exhibit greater circadian sensitivity to short-wavelength radiation compared to adults. As for threshold, it takes longer to observe significant melatonin suppression at lower CS levels than at higher CS levels. Doseresponse curves (amount and duration) for both white-light spectra and both age groups can guide lighting recommendations when considering circadian-effective light in applications such as offices, schools, residences, and healthcare facilities.

Light Pollution, Circadian Photoreception, and Melatonin in Vertebrates

“…The participants' age ranged from childhood (nine years) [135] to senior citizen (mean ± SD: 72.8 ± 6.5 years) [119]. Two studies evaluated adolescents (age 13-18 years) and compared the results with adult participants [136,137]. Mean age of participants was 25 years in eight studies [123,124,[126][127][128][129]133,138], with a range of 18 to 30 years in eleven studies [117,121,122,127,131,[139][140][141][142][143][144].…”

“…Mean age of participants was 25 years in eight studies [123,124,[126][127][128][129]133,138], with a range of 18 to 30 years in eleven studies [117,121,122,127,131,[139][140][141][142][143][144]. Participants with an age range to 40 years were included in six studies [125,132,[145][146][147][148], those with an age range to 50 years were included in three studies [134,136,149], and those with an age range from 18 to 60 years were included in four studies [120,137,150,151]. Table 5.…”

“…Illuminance <1 lx was analyzed in one study [139], illuminance <5 lx was analyzed in four studies [119,129,131,134], and illuminance <10 lx was analyzed in five studies [127,130,142,145,147]. Illuminance up to 100 lx was used in four studies [120,121,138,150] and illuminance up to 250 lx was used in several studies [120,124,[127][128][129]131,[135][136][137]140,143,145,147,151]. More than one illuminance was tested in several studies [117,120,123,124,128,131,134,135,139,143,145,147,[149][150][151].…”

“…Polychromatic light was used in most studies [117,122,124,126,127,129,131,134,138,139,[141][142][143][145][146][147][149][150][151]. Some studies examined effects of monochromatic light [120,144], LED monochromatic light [123,132,148], or LED polychromatic light [136,137]. Two studies used incandescent light [122,128].…”

“…Two studies used CCT >6500 K [141,150]. One study tested illuminance under seven different CCTs ranging from 1600 to 14,000 K [141]; in one study, the authors used 2700 K and 5600 K [136], and, in one study, they used 2700 K and 6500 K [137]. The CCT was not defined in several studies [119,[123][124][125]128,130,[132][133][134][135]138,144,145,148,149].…”