Carryover effects in melatonin suppression
| ISRCTN | ISRCTN38107747 |
|---|---|
| DOI | https://doi.org/10.1186/ISRCTN38107747 |
- Submission date
- 20/06/2025
- Registration date
- 30/06/2025
- Last edited
- 30/06/2025
- Recruitment status
- No longer recruiting
- Overall study status
- Ongoing
- Condition category
- Other
Plain English summary of protocol
Background and study aims
Exposure to light in the evening or at night can reduce how much melatonin your body produces. Melatonin is a hormone that helps you feel sleepy. Evening light can also shift your body clock, making it harder to fall asleep and possibly affecting your sleep quality. However, we still don’t fully understand how melatonin levels vary from day to day, or how light exposure on the days before affects this.
This study aims to learn how different levels of evening light affect the body and behaviour. We are studying this in healthy adults between 18 and 40 years old.
Who can participate?
Healthy adults aged 18 to 40 years who are in good physical and mental health and have healthy vision can participate. Participants can be men, women with a natural menstrual cycle, or women who take a specific type of birth control pill.
What does the study involve?
Each participant goes through all parts of the study and serves as their own control. The study has three parts:
Week at home – Participants follow their usual routine for one week while we record their sleep, physical activity, light exposure, and glucose levels.
Ten days in the laboratory – Participants come to the laboratory for six hours each evening. They are exposed to different light levels (dim or bright light). We collect saliva samples every 30 minutes to measure melatonin. Participants also complete short questionnaires every 30 minutes about how sleepy they feel and how comfortable they find the room temperature. Every hour, they take a short attention test. We also measure their skin and core body temperature during the laboratory visits.
Week at home again – After the laboratory period, participants return to their normal routine for one more week while we continue to collect data.
What are the possible benefits and risks of participating?
Participants will receive personal health feedback, including insights into their sleep and glucose patterns. They will receive EUR540 for completing the full study.
There are no major medical risks. However, some people may feel tired from the laboratory visits. The glucose sensor may also cause mild skin irritation.
Where is the study run from?
The study is run by the Technical University of Munich, in collaboration with the Professorship for Chronobiology and Health and the Chair for Engineering and Design.
When is the study starting and how long is it expected to run for?
The study was planned in January 2025. Recruitment started in May 2025, after ethics approval. We expect to complete the last experiments by August 2025.
Who is funding the study?
This work is funded by internal sources and by the TUM Institute for Advanced Study (IAS), Focus Group Human-Centric Building Performance (Germany)
Who is the main contact?
Letizia Wörrlein, letizia.woerrlein@tum.de
Contact information
Public
Department Health and Sport Sciences
Technical University of Munich
Am Olympiacampus 11
Munich
80809
Germany
 ORCID ID |
0009-0001-3104-1249 |
|---|---|
| Phone | +49 (0)89 289 - 24544 |
| letizia.woerrlein@tum.de |
Scientific, Principal Investigator
Department Health and Sport Sciences
Technical University of Munich
Am Olympiacampus 11
Munich
80809
Germany
| ORCID ID |
0000-0002-8572-9268 |
|---|---|
| Phone | +49 (0)89 289 - 24544 |
| manuel.spitschan@tum.de |
Study information
| Study design | Interventional randomized cross over trial |
|---|---|
| Primary study design | Interventional |
| Secondary study design | Randomised cross over trial |
| Study setting(s) | Home, Laboratory |
| Study type | Other, Prevention, Quality of life |
| Participant information sheet | 47535 20250428_CarryoverMelatoninSuppression_ParticipantInformationSheet.pdf |
| Scientific title | Carryover effects in melatonin suppression during repeated light exposure in healthy adults: a within-subject controlled trial |
| Study acronym | AFTERGLOW |
| Study objectives | Primary hypotheses: H1: Light exposure (1000 lx) leads to greater melatonin suppression compared to dim light (10 lx). H2: The impact of light exposure on melatonin suppression is modulated by prior light history. H3: Individual variability in melatonin suppression is significant. Secondary hypotheses: H4: Bright light exposure reduces subjective sleepiness compared to dim light. H5: Bright light exposure enhances psychomotor vigilance. H6: Core body temperature follows a different trajectory under bright vs. dim light. H7: Distal-proximal skin temperature gradient follows a different trajectory under bright vs. dim light. H8: Bright light exposure influences glucose metabolism. |
| Ethics approval(s) |
Approved 07/05/2025, Ethics Committee at the Technical University of Munich (Grillparzerstraße 16, Munich, 81675, Germany; +49 89 4140-7737; ethikkommission@mri.tum.de), ref: 2025-164-S-SB |
| Health condition(s) or problem(s) studied | Chronobiology, melatonin suppression |
| Intervention | This ten-day in-laboratory within-subject study in healthy adults aged 18-40 years examines melatonin suppression and potential carryover effects of repeated evening light exposure (dim light 10 lx, bright light 1000 lx), with light exposure sequence determined by a 2-label, 3-level counterbalanced De Bruijn sequence with no masking applied. After successful screening, participants are invited to visit the laboratory to sign the informed consent and collect the study devices. They will begin with a 7-day ambulatory pre-laboratory period, during which they follow their regular routines while wearing an ActiGraph (to monitor physical activity and sleep), an ActLumus (to measure light exposure), and a continuous glucose monitor (CGM) for interstitial glucose levels. During this period, participants complete a daily sleep questionnaire each morning upon waking and roughly record their food and drink intake as well as physical activity. This is followed by a 10-day sequential laboratory stay. Participants arrive at the laboratory 6.5 hours before their habitual bedtime, where they receive a standardized meal tailored to their anthropometric measurements. After a 60-minute rest, they spend 3 hours in dim light conditions (10 lx), followed by a 1.5-hour exposure period to either 10 lx or 1000 lx lighting. Skin and core body temperature are continuously measured throughout the laboratory stay. Participants leave the laboratory 30 minutes before their habitual bedtime. To address potential evening hunger, an optional snack is provided for the way home. This is intended to prevent compensatory overeating later in the evening, which could negatively impact sleep onset and overall sleep quality. During the laboratory stay, saliva samples are collected every 30 minutes to assess melatonin levels. Every 30 minutes, participants complete sleepiness and visual comfort questionnaires, and every 60 minutes, they perform a psychomotor vigilance test (PVT). The laboratory period is concluded by a final 7-day post-laboratory period at home. |
| Intervention type | Mixed |
| Primary outcome measure | Melatonin concentrations (pg/mL) are determined from saliva samples collected at 30-minute intervals throughout each of the ten evenings in the laboratory. |
| Secondary outcome measures | 1. Subjective sleepiness measured using Karolinska Sleepiness Scale (KSS) scores at 30-minute intervals throughout each of the ten evenings in the laboratory. 2. Reaction time (ms) measured using the psychomotor vigilance test (PVT) at 60-minute intervals throughout each of the ten evenings in the laboratory. 3. Core body temperature measured continuously during each of the ten evenings in the laboratory using indigestible pills by BodyCap. 4. Skin temperature measured continuously during each of the ten evenings in the laboratory using iButtons attached to the ankle (distal) and neck (proximal). 5. Interstitial glucose levels measuring using the continuous glucose monitor during the ambulatory pre-laboratory, laboratory and post-laboratory period. |
| Overall study start date | 30/01/2025 |
| Completion date | 14/08/2025 |
Eligibility
| Participant type(s) | Healthy volunteer, Learner/student |
|---|---|
| Age group | Adult |
| Lower age limit | 18 Years |
| Upper age limit | 40 Years |
| Sex | Both |
| Target number of participants | 16 |
| Key inclusion criteria | 1. Age: ≥ 18, ≤ 40 years of age 2. Biological sex: men / women with a natural menstrual cycle / women taking monophasic combined oral contraceptives 3. Good physical health 4. Good mental health 5. Good ocular health 6. Normal color vision 7. Ability to comprehend and communicate in basic Englisch |
| Key exclusion criteria | 1. Biological sex: women taking any other type of hormonal contraception 2. BMI: <18 / >30 years 3. Any use of medications 4. Habitual smoking 5. Diagnosis of epilepsy 6. Excessive alcohol use 7. Poor sleep quality 8. Extreme chronotype 9. Shift work in the past 3 months 10. Inter-time zone travel in the past 3 months 11. Currently pregnant and <12 months postpartum 12. Any hormonal imbalances 13. Any drug detected 14. Any alcohol in breath |
| Date of first enrolment | 12/05/2025 |
| Date of final enrolment | 30/06/2025 |
Locations
Countries of recruitment
- Germany
Study participating centre
Munich
80333
Germany
Sponsor information
University/education
Department Health and Sport Sciences
Technical University of Munich
Am Olympiacampus 11
Munich
80909
Germany
| Phone | +49 (0)89 289 - 24544 |
|---|---|
| info.chronobiology@mh.tum.de | |
| Website | https://www.hs.mh.tum.de/en/chronobiology/home/ |
Funders
Funder type
Other
No information available
Results and Publications
| Intention to publish date | 31/08/2026 |
|---|---|
| Individual participant data (IPD) Intention to share | Yes |
| IPD sharing plan summary | Stored in publicly available repository |
| Publication and dissemination plan | The results of this study will be published without any reservations as a peer-reviewed article. The article will be preprinted on bioRxiv. |
| IPD sharing plan | All data to be published will be stored in anonymized form in the Professorship´s GitHub repository at github.com/tscnlab. Data will be available under an open licence, and after informed consent is obtained from participants. A permalink will be generated on Zenodo, and this information updated here. |
Study outputs
| Output type | Details | Date created | Date added | Peer reviewed? | Patient-facing? |
|---|---|---|---|---|---|
| Participant information sheet | 30/06/2025 | No | Yes | ||
| Protocol file | 30/06/2025 | No | No |
Additional files
Editorial Notes
23/06/2025: Trial's existence confirmed by TUM.
