Effects of a violet-excitation light-emitting diode on melatonin secretion and sleepiness: preliminary findings from a randomized controlled trial
ABSTRACT
Study Objectives:
A new type of lighting using violet-excitation light-emitting diodes (LEDs) with an action spectrum centered at approximately 405 nm was developed. Although violet-excitation LEDs can reduce melatonin suppression compared with blue-excitation LEDs, no studies have compared the effects of violet-excitation LEDs with those of blue-excitation LEDs on melatonin suppression. This study was designed to compare the effects of violet-excitation LEDs with those of blue-excitation LEDs on melatonin suppression, psychomotor vigilance, and sleepiness.
Methods:
Sixteen healthy Japanese males aged 20–39 years were exposed to violet- and blue-excitation LEDs for 3 hours in a crossover randomized manner. The primary outcome was changes in salivary melatonin levels compared with the baseline levels. The secondary outcomes were changes in psychomotor vigilance and the Karolinska Sleepiness Scale. Melatonin suppression was calculated from the difference in the area under the curves between the baseline and intervention.
Results:
Of the 16 participants, 15 completed the measurements. The baseline characteristics did not differ significantly between the 2 groups. After adjusting for age, a difference of 16.28 pg/mL in mean melatonin suppression was observed between the violet- and blue-excitation LED groups (−2.15 pg/mL vs −18.43 pg/mL; P = .006). The overall melatonin suppression by violet-excitation LEDs was 48.6% smaller than that by blue-excitation LEDs. No significant differences in psychomotor vigilance and sleepiness were observed between the 2 groups.
Conclusions:
Melatonin suppression in healthy Japanese males exposed to violet-excitation LEDs was significantly smaller than that in those exposed to blue-excitation LEDs. Our preliminary findings indicate that violet-excitation LEDs may have the potential to reduce the magnitude of blue-excitation LED-induced melatonin suppression.
Citation:
Mitsui K, Saeki K, Sun M, Yamagami Y, Tai Y, Obayashi K. Effects of a violet-excitation light-emitting diode on melatonin secretion and sleepiness: preliminary findings from a randomized controlled trial. J Clin Sleep Med. 2024;20(1):101–109.
BRIEF SUMMARY
Current Knowledge/Study Rationale: A new type of light-emitting diodes (LEDs) using violet light as excitation light instead of blue light may reduce melatonin suppression in our modern life. The present study compared the effects of melatonin suppression between violet-excitation LEDs and blue-excitation LEDs.
Study Impact: Melatonin suppression caused by violet-excitation LEDs was significantly smaller than that by blue-excitation LEDs, suggesting that violet-excitation LEDs could be used as a nighttime light source to reduce melatonin suppression.
INTRODUCTION
Melatonin is a pineal gland hormone that has diurnal secretion rhythms controlled by the suprachiasmatic nucleus. Melatonin secretion is detectable approximately 2 hours prior to sleep onset and peaks around the core body temperature minimum.1 Melatonin is an output of and input to the circadian timekeeping system. Recent epidemiological studies suggest that decreased physiological melatonin levels are associated with adverse health outcomes, such as diabetes mellitus, atherosclerosis, cardiovascular diseases, dementia, depression, and cancer.2–6 Therefore, maintaining physiological melatonin levels may be important in preventing several diseases.
It is well recognized that melatonin is suppressed by light during the secretion period.7,8 This melatonin suppression is the strongest by short-wavelength light at approximately 460 nm because intrinsically photosensitive retinal ganglion cells, which are the light receptors on the retina related to biological rhythms, are most sensitive to this wavelength range.9,10 In modern society, from the viewpoint of energy saving, light-emitting diodes (LEDs) are widely used for indoor/outdoor environment lighting. However, LEDs produce short-wavelength light at approximately 460 nm, and thus melatonin suppression may occur frequently in our daily life.11,12
Recently, a new type of LEDs that emit violet-excitation light centered at approximately 405 nm have been increasingly utilized, instead of blue-excitation LEDs centered at approximately 460 nm. Now, polychromatic light using violet-excitation LEDs is used in specific places, including art museums and operating rooms, where accurate color rendering is needed. The wavelength of violet-excitation LEDs is distant from the action spectrum of melatonin suppression, unlike that of blue-excitation LEDs; therefore, violet-excitation LEDs are expected to produce less melatonin suppression compared with blue-excitation LEDs.13–15 However, to the best of our knowledge, no studies have compared the effects of violet-excitation LEDs with those of blue-excitation LEDs on melatonin suppression. This randomized controlled trial was designed to compare the nighttime effects of violet-excitation LEDs with those of blue-excitation LEDs on melatonin suppression, psychomotor vigilance, and sleepiness in young males.
METHODS
Participants
To minimize the effects of sex and age on melatonin secretion, only males aged between 20 and 39 years were included in this study. The exclusion criteria were as follows: individuals with any medication use, those with any eye disease, those with any psychiatric illness, those with any current dental treatment, current smokers, current shift-workers, those with sleep disturbances (Pittsburgh Sleep Quality Index score ≥ 6), extreme chronotype individuals (Morningness–Eveningness Questionnaire score ≤ 30 or ≥ 70), and those who traveled abroad in the past 3 months. Sixteen healthy participants were enrolled using the participant recruitment system of a commercial agency (3H Medi Solution Inc., Tokyo, Japan).
Study design and procedure
In the first session, the participants were randomly assigned to 2 groups, the violet-excitation LED group or the blue-excitation LED group (Figure 1). Then, in the second session, the participants were assigned to the other intervention after a washout period of 7 days. A research assistant (T.W.), who did not know the participants’ information, conducted block randomization (block number = 2) using computer-generated random sequences. The participants were blinded to the intervention assignment.
Reasons for exclusion are stated on the right. Violet LED = violet-excitation light-emitting diode, Blue LED = blue-excitation light-emitting diode.
The participants were instructed to keep their habitual sleep–wake patterns for 1 week before the intervention sessions. We monitored the sleep–wake patterns of the participants using actigraphy (wGT3×-BT; ActiGraph, Pensacola, Florida) and a standardized sleep diary. The intake of alcohol and caffeine was prohibited from the day before the intervention sessions. In the laboratory, the participants were seated on a bed and instructed to remain awake and wear welding goggles (425 IR5; Toabojin, Osaka, Japan) when going to the bathroom. The light transmittance rate of the goggles was 0.75%. All intervention sessions were performed in the laboratory of KYOCERA Corporation, Shiga, Japan. The study protocol was registered at the Japan Registry of Clinical Trials (jRCT 1030200061). The Institutional Review Board of the Japanese Society for Wellbeing Science and Assistive Technology approved this study, and written informed consent was obtained from all participants.
Intervention sessions
In the intervention sessions, baseline measurement was performed on day 1, and lighting interventions (exposure to violet- or blue-excitation LEDs for 3 hours) were performed on day 2 (Figure 2). In the laboratory, to control the participants’ light history, ambient light intensity and color temperature were maintained at 50 lux and 3,000 K from 9:00 until 18:00 (4 hours before the light interventions) and 2 lux and 3,000 K from 18:00 until 20:00 (2 hours before the light interventions) using an adjustable illuminance light (Hue; Signify, Eindhoven, The Netherlands). For dark adaptation, ambient light intensity was kept at 0 lux from 20:00 until 22:00 (before the light interventions). The participants were directed not to use light-emitting devices in the sessions. The intervention sessions were initiated approximately 15 hours before (9:00 in Figure 2) each participant’s habitual bedtime and finished 1 hour after (1:00 in Figure 2) the habitual bedtime. Although the time of day in Figure 2 was based on the average bedtime of all participants (ie, average bedtime was about 00:00), the intervention and data collection schedule for each participant was based on each participant’s habitual bedtime.
Saliva melatonin levels and Karolinska Sleepiness Scale scores were measured at 30-minute intervals (black triangles), and the psychomotor vigilance task was performed hourly (white triangles). The representative times in the figure are average times calculated by the time schedules of all participants. The time schedule for each participant was based on his habitual bedtime. Violet LED = violet-excitation light-emitting diode, Blue LED = blue-excitation light-emitting diode.
Violet- and blue-excitation LEDs
The light interventions were administered using a specially developed violet-excitation LED (CERAPHIC; KYOCERA Corp., Kyoto, Japan) and a generally marketed blue-excitation LED (LDA7DGZ60ESW; Panasonic Corp., Osaka, Japan). The blue-excitation LED has a peak spectral power of approximately 460 nm, which is the strongest signal to intrinsically photosensitive retinal ganglion cells, whereas the spectral power of the violet-excitation LED was very low (Figure 3A).
(A) Distribution in irradiance of violet- (solid line) and blue-excitation light-emitting diodes (LEDs) (dotted line). (B) α-opic equivalent daylight (D65) illuminance in the 5 known human opsins of violet- (black bars) and blue-excitation LEDs (white bars). lc = l-cone-opic, mc = M-cone-opic, mel = melanopic, rh = rhodopic, Sc = S-cone-opic. (C) Photopic illuminances of violet- (black bar) and blue-excitation LEDs (white bar).
An α-opic equivalent daylight (D65) illuminance was proposed to quantify the effective impact of each of the 5 known human opsins,16 where melanopic equivalent daylight (D65) illuminance is closely associated with the effective impact on intrinsically photosensitive retinal ganglion cells. The violet-excitation LED has a lower melanopic equivalent daylight (D65) illuminance than the blue-excitation LED (36 lux vs 142 lux, respectively) (Figure 3B). The 2 LEDs have equal overall photopic illuminance (158.5 lux) (Figure 3C) and photon irradiance (1.4 × 1018 s−1 m−2). The violet-excitation LED has a lower color temperature than the blue-excitation LED (2,522 K vs 6,256 K, respectively). These illuminance parameters were measured using an illuminance spectrometer (CL-500A; Konica Minolta Inc., Tokyo, Japan) at the participants’ eye level. All light sources were installed in the ceiling, and the participants were prohibited from looking at the light sources directly.
Measurement of melatonin
Saliva melatonin levels were assessed from saliva samples collected at 30-minute intervals from 2.5 hours before the light interventions (Figure 2). All samples were collected using cotton swabs (Salivette; Sarstedt, Nümbrecht, Germany) and were immediately frozen and stored at −20°C until assays. In a commercial laboratory, blinded to the participant’s light condition, melatonin concentrations were assayed using an enzyme-linked immunosorbent assay kit (EK-DSM; Bühlmann, Schönenbuch, Switzerland). The detection limit was 0.5 pg/mL, and intra- and interassay precision was 12.6% and 22.9%, respectively. Outliers were defined using the boxplot approach, which excluded data far from the first and third quartile by 1.5 times the interquartile range.
Measurement of psychomotor vigilance and sleepiness
Sustained attention was assessed using a visual 10-minute psychomotor vigilance task using software (PC-PVT 2.0; Biotechnology High Performance Computing Software Applications Institute, Frederick, Maryland) at 1-hour intervals from 2.5 hours before the light interventions (Figure 2).17,18 The participants were instructed to quickly press a mouse button as fast as a time counter that incremented the number at every 1 ms was presented on a computer display. Light exposure from the display was controlled to be < 2 lux at the participants’ eye level. The time counter was presented at random intervals from 2 to 10 seconds. The time required to press the mouse button was recorded as the reaction time (RT). The mean RT and number of lapses (RT > 500 ms) in a 10-minute session were calculated. A higher RT or number of lapses indicates lower performance. The participants were allowed to practice once before the first measurement. Self-reported sleepiness was evaluated using the Japanese version of the Karolinska Sleepiness Scale (KSS) at 30-minute intervals from 2.5 hours before the light interventions (Figure 2).19,20 Scores on the KSS ranged from 1 to 9 points, with a higher score indicating more sleepiness.
Statistical analysis
The sample size was estimated based on our unpublished pilot data. We assumed an effect size of 0.98 (Cohen’s dz) with a two-tailed significance level of .05 and a power of 80% to detect a difference and a dropout rate of 30%. Using G*Power (version 3.1.9.7), the estimated sample size was 1121; however, considering dropouts, the total sample size was estimated to be 16.
The primary outcome was melatonin suppression by the light interventions, which was calculated from the difference in the area under the curve (AUC) between the baseline and intervention during the light intervention (3 hours), as follows: overall melatonin suppression (percent) = (AUCbaseline − AUCintervention)/AUCbaseline × 100. The secondary outcomes were changes in the RT, number of lapses, and KSS score, from the baseline after the light interventions. We used reciprocal-transformed data (1/RT) to maximize sensitivity to emphasize small changes.22 Changes from the baseline after the interventions were evaluated using the mixed-effect linear regression analysis, consisting of individual-level variables (ie, age) and measurement-level variables (ie, light conditions, melatonin levels, 1/RT, the number of lapses, KSS scores, and times). Melatonin levels, 1/RT, and the number of lapses were included as dependent variables. The regression slopes were assumed to be fixed effects, whereas the intercepts were assumed to be random effects. The random effects covariance matrices were considered to be unstructured, and the restricted maximum likelihood was used for estimation of regression coefficients. The overall melatonin suppression was compared between the 2 light conditions using Wilcoxon’s test. All statistical analyses were performed using Statistical Package for the Social Sciences (version 27.0; IBM Corp., Armonk, New York). Two-sided P values of less than .05 were used to denote statistical significance.
RESULTS
Of the 16 participants enrolled in this study, 1 participant was excluded because he did not come to the test site. Therefore, 15 participants were randomly assigned to the 2 intervention groups. Eight participants were assigned to the violet-excitation LED group in the first session and then to the blue-excitation LED group in the second session, and 7 participants were assigned to the blue-excitation LED group in the first session and then to the violet-excitation LED group in the second session (Figure 1).
The mean age of the 15 participants was 26.3 ± 5.9 years. The mean bedtime, rising time, and duration in bed were 23:57 ± 0:41, 8:07 ± 0:35, and 466.3 ± 33.8 minutes, respectively. The median global score of the participants in the Pittsburgh Sleep Quality Index was 2.0 (interquartile range, 2.0–3.0), and the mean Morningness–Eveningness Questionnaire score was 53.9 ± 6.2. No significant differences in these baseline characteristics were observed between the 2 intervention groups (Table 1).
| Characteristics | Intervention Sequence | ||
|---|---|---|---|
| Violet LED to Blue LED | Blue LED to Violet LED | P | |
| No. of participants | 8 | 7 | |
| Age, mean ± SD, y | 26.8 ± 7.5 | 25.7 ± 4.7 | .75 |
| Bedtime, mean ± SD, clock time | 23:55 ± 0:50 | 0:00 ± 0:34 | .83 |
| Rising time, mean ± SD, clock time | 8:03 ± 0:37 | 8:12 ± 0:38 | .63 |
| Duration in bed, mean ± SD, min | 464 ± 44 | 469 ± 25 | .77 |
| PSQI global score, median [IQR] | 2.5 [1.3–3.8] | 2.0 [2.0–3.0] | .87 |
| MEQ score, mean ± SD | 56.1 ± 6.0 | 51.4 ± 6.3 | .17 |
The time-dependent changes in melatonin concentration without outliers (percentage of outliers in violet- and blue-excitation LED was 12.78% and 11.67%, respectively) from the baseline under the 2 light conditions are shown in Figure 4A. In the mixed-effect linear regression analysis, the mean melatonin suppression per measurement during the light interventions was significantly lower in the violet-excitation LED group than in the blue-excitation LED group (−1.52 pg/mL vs −17.78 pg/mL) (Table 2). Age-adjusted statistical models suggested similar results, where melatonin suppression was significantly lower in the violet-excitation LED group than in the blue-excitation LED group (adjusted difference: 16.28 pg/mL; 95% confidence interval, 4.66–27.90 pg/mL; P = .006). Even after excluding outliers, this result was consistent with those of the analysis of all melatonin level data (adjusted difference: 4.09 pg/mL; 95% confidence interval, 2.12–6.05 pg/mL; P < .001). The overall melatonin suppression by the violet-excitation LED during the light interventions calculated from the differences in the AUC values between the baseline and intervention was 48.6% smaller than that by the blue-excitation LED (19.6% vs 38.1%; P < .05) (Figure 4B).
(A) Time-dependent changes in the mean salivary melatonin levels compared with the baseline. The nonshaded area indicates data during the light interventions using the violet-excitation (bold line) and blue-excitation light-emitting diodes (LEDs) (thin line). Error bars indicate standard errors. (B) The mean overall melatonin suppression by violet-excitation (black bar) and blue-excitation (white bar) LEDs. Error bars indicate standard errors.
| Changes from the Baseline | ||||
|---|---|---|---|---|
| Violet LED (n = 15) | Blue LED (n = 15) | Difference | ||
| Crude model | Mean [95%CI] | Difference [95%CI] | P | |
| Melatonin, pg/mL | −1.52 [−8.03 to 4.99] | −17.78 [−27.78 to −7.78] | 16.22 [4.60 to 27.84] | .006 |
| PVT | ||||
| 1/RT | 1.32 × 10−4 [−2.32 × 10−5 to 2.87 × 10−4] | 1.00 × 10−4 [−2.11 × 10−5 to 2.21 × 10−4] | 3.17 × 10−5 [−1.50 × 10−4 to 2.13 × 10−4] | .73 |
| Lapses | 0.49 [−2.37 to 3.35] | −0.44 [−3.30 to 2.42] | 0.93 [−2.52 to 4.39] | .59 |
| KSS | −2.19 [−2.54 to −1.84] | −2.20 [−2.55 to −1.85] | 0.01 [−0.36 to 0.38] | .96 |
| Age-adjusted | Adjusted Mean [95%CI] | Difference [95%CI] | P | |
| Melatonin, pg/mL | −2.15 [−12.08 to 7.79] | −18.43 [−28.37 to −8.48] | 16.28 [4.66 to 27.9] | .006 |
| PVT | ||||
| 1/RT | 1.32 × 10−4 [−2.99 × 10−5 to 2.93 × 10−4] | 1.00 × 10−4 [−6.15 × 10−5 to 2.62 × 10−4] | 3.17 × 10−5 [−1.50 × 10−4 to 2.13 × 10−4] | .73 |
| Lapses | 0.49 [−2.94 to 3.92] | −0.44 [−3.87 to 2.98] | 0.93 [−2.52 to 4.39] | .59 |
| KSS | −2.19 [−2.94 to −1.45] | −2.20 [−2.95 to −1.46] | 0.01 [−0.36 to 0.38] | .96 |
Consistently, in the analysis using data in the entire melatonin measurement periods, melatonin suppression was significantly smaller in the violet-excitation LED group than in the blue-excitation LED group (age-adjusted difference: 9.37 pg/mL; 95% confidence interval, 2.65–16.09 pg/mL; P = .006).
Regarding psychomotor vigilance and sleepiness, the time-dependent changes in 1/RT, lapse, and KSS scores from the baseline under the 2 light conditions are shown in Figure 5. No significant differences in any of these parameters were observed between the 2 light conditions (Table 2).
(A) Time-dependent changes in the mean 1/RT compared with the baseline. The nonshaded area indicates data during the light interventions using the violet-excitation (bold line) and blue-excitation (thin line) light-emitting diodes (LEDs). Error bars indicate standard errors. RT = reaction time. (B) Time-dependent changes in the number of lapses compared with the baseline. The nonshaded area indicates data during the light interventions using the violet-excitation (bold line) and blue-excitation (thin line) LEDs. Error bars indicate standard errors. (C) Time-dependent changes in Karolinska Sleepiness Scale scores compared with the baseline. The nonshaded area indicates data during the light interventions using the violet-excitation (bold line) and blue-excitation (thin line) LEDs. Error bars indicate standard errors.
DISCUSSION
This randomized controlled trial demonstrated that melatonin suppression was significantly smaller in the group exposed to the violet-excitation LED than in the group exposed to the blue-excitation LED. The magnitude of reduction in melatonin suppression by the violet-excitation LED was nearly half of that by the blue-excitation LED. In contrast, psychomotor vigilance and sleepiness did not differ significantly between the 2 groups. To the best of our knowledge, this is the first report comparing the effects of a violet-excitation LED with those of a blue-excitation LED on melatonin suppression, psychomotor vigilance, and sleepiness.
A larger reduction in melatonin suppression using violet-excitation LEDs in this study was observed than that by changing the color temperature of light sources in previous studies. A randomized trial reported the effects of changing the color temperature on melatonin suppression, where a low color temperature (4,000 K, 123 lux) reduced melatonin suppression by 40% compared with a high color temperature (17,000 K, 96 lux).23 In contrast, a nonrandomized study reported that although melatonin suppression did not significantly differ among different color temperature conditions (2,800 K vs 9,000 K) in older individuals, a 35.6% reduction in melatonin suppression by a lower color temperature was observed compared with that by a higher color temperature in younger individuals.24 In another nonrandomized study involving children, a lower color temperature (3,041 K) reduced melatonin suppression by 28.4% compared with a higher color temperature (6,218 K).25 Generally, the sensitivity of melatonin suppression in children is greater than that in adults because of the cloudiness of the crystalline lens.26,27 In this randomized controlled study, which involved adults with an average age of 26 years, the violet-excitation LED (2,522 K) reduced melatonin suppression by 48.6% compared with the blue-excitation LED (6,256 K), suggesting that the reduction in melatonin suppression observed in this study was larger than that in previous studies.
With respect to clinical implications, violet-excitation LEDs may have the potential to mitigate the impact of light-induced melatonin suppression with potential ramifications for sleep and even the risk of chronic medical conditions associated with light at night. In recent epidemiological studies, light exposure at night has been reported to be related to the risk of obesity, diabetes mellitus, and atherosclerosis.28–32 These associations are considered to be mediated by physiological melatonin levels.33 The Nurse’s Health Study using urine samples suggested that lower melatonin levels are significantly associated with the incidence of diabetes mellitus and cardiovascular diseases,2,4 suggesting that a 78.5% decrease in urinary melatonin levels (lowest vs highest of melatonin secretion groups in the study) was significantly associated with a 131% higher risk of diabetes mellitus.2 These data suggest that the 19.6% and 38.1% decreases in melatonin levels observed when exposed to violet- and blue-excitation LEDs, respectively, could have important repercussions for diabetes risk. Furthermore, a nested case–control study revealed that a 41.9% decrease in urinary melatonin levels (lowest vs highest of melatonin secretion groups in the study) was significantly associated with a 112% higher risk of myocardial infarction.4 Given the association between reduced melatonin levels and chronic conditions, mitigation of light-induced melatonin suppression with violet-excitation LEDs may have health benefits, but further investigation is required. Thus, using violet-excitation LEDs instead of blue-excitation LEDs may be associated with a 49.4% lower risk of myocardial infarction.
Further studies are warranted to better understand the effects of violet-excitation LEDs on psychomotor vigilance and sleepiness. In this study, no significant differences in vigilance parameters and sleepiness scores were observed between the 2 groups. Considering the installation of violet-excitation LEDs in the workplaces of night-shift workers, it would be better to confirm whether such LEDs impair objective performance or subjective arousal levels due to a changing light spectrum. However, we cannot conclude that there are no significant differences in vigilance parameters and sleepiness scores between the 2 light conditions because of the small sample size. Future studies are needed to investigate the effects of violet-excitation LEDs on psychomotor vigilance and sleepiness.
The strength of this study was that the results can easily be translated to real-life situations because a commercially available and widely used blue-excitation LED was used as a control. Additionally, the study protocol included controlling light conditions during the daytime. Light exposure during daytime affects light sensitivity, which in turn affects melatonin suppression.34 However, this study has some limitations to consider. First, the sample size was estimated to detect the significant difference in melatonin suppression by the 2 LEDs; however, the study sample size was relatively small, and therefore there is uncertainty on the effects of the violet-excitation LED on psychomotor vigilance and sleepiness. Second, only young Japanese males were enrolled in this study. Melatonin secretion profiles are reported to be different between males and females, possibly because of the presence of reproductive hormone receptors on the pineal gland.35–38 In addition, a previous report suggested a sex difference on melatonin suppression caused by light exposure at night.39 With aging, endogenous melatonin levels decrease.40 Also, light transmission to the retina decreases with aging because of crystalline lens cloudiness.27 Thus, there may be age differences in melatonin suppression.26 Racial difference in melatonin suppression by light have also been reported.41 Third, saliva melatonin levels were not measured over the whole night; therefore, the effects of the violet-excitation LED on the overall melatonin secretion overnight were unknown. This may lead to the under- or overestimation of the differences in melatonin suppression between the 2 light conditions. Fourth, although the participants were instructed to maintain face position and gaze and we checked their positions throughout the intervention, we did not measure the light intensity at the cornea level. Finally, the light intensity of the 2 types of LED used in this study was 159 lux; thus, further comparisons using different light intensity levels were not performed. Future studies are needed to better understand melatonin suppression by violet-excitation LEDs with different light intensity levels. Considering these limitations, our findings are considered preliminary. In addition, they are limited to young Japanese males; thus, further studies including participants with different clinical and demographic characteristics are needed to extrapolate our findings.
In conclusion, melatonin suppression in the group exposed to the violet-excitation LED was significantly smaller than that in the group exposed to the blue-excitation LED, where the magnitude of reduction in melatonin suppression by the violet-excitation LED was nearly half that by the blue-excitation LED. In contrast, psychomotor vigilance and sleepiness did not significantly differ between the 2 groups; however, because of the small sample size, further study is needed to investigate the effects of violet-excitation LEDs on psychomotor vigilance and sleepiness.
DISCLOSURE STATEMENT
All authors have seen and approved the manuscript. This study was funded by KYOCERA Corporation. K.M. and M.S. are employed by KYOCERA Corp. K.S. and K.O. received research grants from YKK AP, Inc.; Ushio, Inc.; Tokyo Electric Power Company; EnviroLife Research Institute Co., Ltd.; Sekisui Chemical Co., Ltd; LIXIL Corp.; KYOCERA Corp.; ENDO Lighting Corp.; and Kaneka Corp. Y.Y. and Y.T. report no conflicts of interest.
ABBREVIATIONS
| AUC | area under the curve |
| KSS | Karolinska Sleepiness Scale |
| LED | light-emitting diode |
| RT | reaction time |
REFERENCES
1. . Melatonin in humans. N Engl J Med. 1997;336(3):186–195.
2. . Melatonin secretion and the incidence of type 2 diabetes. JAMA. 2013;309(13):1388–1396.
3. . Association between urinary 6-sulfatoxymelatonin excretion and arterial stiffness in the general elderly population: the HEIJO-KYO cohort. J Clin Endocrinol Metab. 2014;99(9): 3233–3239.
4. . A nested case-control study of the association between melatonin secretion and incident myocardial infarction. Heart. 2017;103(9):694–701.
5. . Physiological levels of melatonin relate to cognitive function and depressive symptoms: the HEIJO-KYO cohort. J Clin Endocrinol Metab. 2015;100(8):3090–3096.
6. . Urinary melatonin levels and postmenopausal breast cancer risk in the Nurses’ Health Study cohort. Cancer Epidemiol Biomarkers Prev. 2009;18(1):74–79.
7. . Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression. J Physiol. 2000;526(Pt 3):695–702.
8. . Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans. J Clin Endocrinol Metab. 2011;96(3):E463–E472.
9. . Melanopsin-containing retinal ganglion cells: architecture, projections, and intrinsic photosensitivity. Science. 2002;295(5557):1065–1070.
10. . Phototransduction by retinal ganglion cells that set the circadian clock. Science. 2002;295(5557):1070–1073.
11. . Spectral identification of lighting type and character. Sensors (Basel). 2010;10(4):3961–3988.
12. . Limiting the impact of light pollution on human health, environment and stellar visibility. J Environ Manage. 2011;92(10):2714–2722.
13. . Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor. J Neurosci. 2001;21(16):6405–6412.
14. . High sensitivity of the human circadian melatonin rhythm to resetting by short wavelength light. J Clin Endocrinol Metab. 2003;88(9):4502–4505.
15. . Spectral responses of the human circadian system depend on the irradiance and duration of exposure to light. Sci Transl Med. 2010;2(31):31ra33.
16. CIE. S 026/E:2018. CIE System for Metrology of Optical Radiation for ipRGC-Influenced Responses to Light. Vienna: CIE Central Bureau; 2018.
17. . PC-PVT: a platform for psychomotor vigilance task testing, analysis, and prediction. Behav Res Methods. 2014;46(1):140–147.
18. . PC-PVT 2.0: an updated platform for psychomotor vigilance task testing, analysis, prediction, and visualization. J Neurosci Methods. 2018;304:39–45.
19. . Subjective and objective sleepiness in the active individual. Int J Neurosci. 1990;52(1-2):29–37.
20. . Validation of the Karolinska sleepiness scale against performance and EEG variables. Clin Neurophysiol. 2006;117(7):1574–1581.
21. . G*Power 3: a flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behav Res Methods. 2007;39(2):175–191.
22. . Maximizing sensitivity of the psychomotor vigilance test (PVT) to sleep loss. Sleep. 2011;34(5):581–591.
23. . Randomized trial of polychromatic blue-enriched light for circadian phase shifting, melatonin suppression, and alerting responses. Physiol Behav. 2019;198:57–66.
24. . Differential impact in young and older individuals of blue-enriched white light on circadian physiology and alertness during sustained wakefulness. Sci Rep. 2017;7(1):7620.
25. . Melatonin suppression and sleepiness in children exposed to blue-enriched white LED lighting at night. Physiol Rep. 2018;6(24):e13942.
26. . Influence of light at night on melatonin suppression in children. J Clin Endocrinol Metab. 2014;99(9):3298–3303.
27. . Circadian photoreception: ageing and the eye’s important role in systemic health. Br J Ophthalmol. 2008;92(11):1439–1444.
28. . Association of exposure to artificial light at night while sleeping with risk of obesity in women. JAMA Intern Med. 2019;179(8):1061–1071.
29. . Ambient light exposure and changes in obesity parameters: a longitudinal study of the HEIJO-KYO cohort. J Clin Endocrinol Metab. 2016;101(9):3539–3547.
30. . Bedroom lighting environment and incident diabetes mellitus: a longitudinal study of the HEIJO-KYO cohort. Sleep Med. 2020;65:1–3.
31. . Light at night in older age is associated with obesity, diabetes, and hypertension. Sleep. 2023;46(3):zsac130.
32. . Indoor light pollution and progression of carotid atherosclerosis: a longitudinal study of the HEIJO-KYO cohort. Environ Int. 2019;133(Pt B):05184.
33. . Light at night as an environmental endocrine disruptor. Physiol Behav. 2018;190:82–89.
34. . The effects of prior light history on the suppression of melatonin by light in humans. J Pineal Res. 2002;33(4):198–203.
35. . Lower melatonin secretion in older females: gender differences independent of light exposure profiles. J Epidemiol. 2015; 25(1):38–43.
36. . Sex differences in the circadian profiles of melatonin and cortisol in plasma and urine matrices under constant routine conditions. Chronobiol Int. 2016;33(1):39–50.
37. . Seasonal variation of gonadotropins and gonadal steroids receptors in the human pineal gland. Brain Res Bull. 1997;44(6):665–670.
38. . The crosstalk between melatonin and sex steroid hormones. Neuroendocrinology. 2022;112(2):115–129.
39. . Does bright light suppress nocturnal melatonin secretion more in women than men? J Neural Transm Gen Sect. 1995;102(1):75–80.
40. . Aging and circadian rhythms. Sleep Med Clin. 2015;10(4):423–434.
41. . Influence of eye colors of Caucasians and Asians on suppression of melatonin secretion by light. Am J Physiol Regul Integr Comp Physiol. 2007;292(6):R2352–R2356.
