How sex hormones influence melatonin suppression by evening light in healthy adults
| ISRCTN | ISRCTN38686596 |
|---|---|
| DOI | https://doi.org/10.1186/ISRCTN38686596 |
| Sponsor | Max Planck Society |
| Funder | Max-Planck-Gesellschaft |
- Submission date
- 09/01/2026
- Registration date
- 18/01/2026
- Last edited
- 15/01/2026
- Recruitment status
- Recruiting
- Overall study status
- Ongoing
- Condition category
- Other
Plain English summary of protocol
Background and study aims
Light exposure in the evening can reduce the hormone melatonin, which is involved in sleep regulation. People differ widely in how strongly their melatonin levels are suppressed by light, and sex hormones may contribute to these differences. This study investigates how natural and contraceptive-related sex hormones influence melatonin suppression and sensitivity of the eye to light.
Who can participate?
Healthy adults aged 23–35 years, including naturally cycling women, women using oral contraceptives, and men.
What does the study involve?
Participants attend five evening laboratory sessions. During each session, saliva samples are collected to measure melatonin levels, pupil responses to light are measured, and participants are exposed to either dim light or bright light using a virtual reality headset.
What are the possible benefits and risks?
There are no direct health benefits. Risks are minimal and may include temporary eye discomfort or changes in sleepiness following evening light exposure.
Where is the study run from?
Max Planck Institute for Biological Cybernetics (Germany)
When is the study starting and how long is it expected to run for?
January 2026 to December 2027
Who is funding the study?
Max Planck Society (Germany)
Who is the main contact?
Carolina Guidolin, carolina.guidolin@tuebingen.mpg.de
Contact information
Public, Scientific
Max Planck Institute for Biological Cybernetics
Tübingen
72076
Germany
 ORCID ID |
0009-0007-4959-2667 |
|---|---|
| Phone | +49 (0)7071 601 217 |
| carolina.guidolin@tuebingen.mpg.de |
Principal investigator
Max Planck Institute for Biological Cybernetics
Tübingen
72076
Germany
| ORCID ID |
0000-0002-8572-9268 |
|---|---|
| Phone | +49 (0)7071 601 1670 |
| carolina.guidolin@tuebingen.mpg.de |
Study information
| Primary study design | Interventional | |
|---|---|---|
| Allocation | N/A: single arm study | |
| Masking | Open (masking not used) | |
| Control | Uncontrolled | |
| Assignment | Single-intervention, repeated-measures, within-subjects; three groups (naturally cycling individuals, individuals using the monophasic combined oral contraceptive pill, healthy male participants) | |
| Purpose | Basic science | |
| Scientific title | Influence of sex steroid hormones on melatonin suppression and retinal light sensitivity during evening light exposure in healthy adults | |
| Study acronym | SHINE | |
| Study objectives | 1. To assess whether endogenous and exogenous sex steroid hormones influence the degree of melatonin suppression induced by evening light exposure 2. To determine whether sex steroid hormones influence retinal light sensitivity, measured using melanopsin-mediated pupil responses | |
| Ethics approval(s) |
Approved 10/11/2025, TUM Ethics Committee (Office of the TUM Ethics Committee, TUM School of Medicine and Health, Munich, 81675, Germany; +49 (0)89 4140 7737; ethikkommission@mri.tum.de), ref: 2025-468-S-NP | |
| Health condition(s) or problem(s) studied | Light-induced melatonin suppression; non-visual physiological responses to light | |
| Intervention | This single-centre laboratory study uses a repeated-measures, within-subject design. Participants complete five evening laboratory sessions: one dim-light control session and four bright-light exposure sessions. Light exposure is delivered using a head-mounted virtual reality display providing approximately 90 lux melanopic equivalent daylight illuminance at eye level. Melatonin suppression is assessed using repeated salivary melatonin measurements collected before, during, and after light exposure. Retinal light sensitivity is assessed using pupillometry with melanopsin-directed silent substitution stimuli. Naturally cycling participants are measured across four distinct menstrual cycle phases, oral contraceptive users across pill-cycle phases, and male participants across a matched time period. | |
| Intervention type | Other | |
| Primary outcome measure(s) |
| |
| Key secondary outcome measure(s) | ||
| Completion date | 31/12/2027 |
Eligibility
| Participant type(s) | |
|---|---|
| Age group | Adult |
| Lower age limit | 23 Years |
| Upper age limit | 35 Years |
| Sex | All |
| Target sample size at registration | 36 |
| Key inclusion criteria | 1. Age 23–35 years 2. Good physical and mental health 3. Normal or corrected-to-normal visual acuity and normal colour vision 4. Regular sleep–wake behaviour 5. For naturally cycling participants: regular menstrual cycles (26–35 days) 6. For oral contraceptive users: stable intake of monophasic combined oral contraceptive for ≥6 months |
| Key exclusion criteria | 1. Chronic medical, hormonal, ocular, neurological or psychiatric disorders 2. Regular use of systemic medication (except anti-allergic medication) 3. Shift work or inter-time-zone travel in the last month 4. Extreme chronotype or excessive daytime sleepiness 5. Current or recent pregnancy or breastfeeding 6. Intake of exogenous hormones other than contraceptive hormones 7. Substance abuse, excessive alcohol consumption, or recreational drug use |
| Date of first enrolment | 15/01/2026 |
| Date of final enrolment | 15/06/2027 |
Locations
Countries of recruitment
- Germany
Study participating centres
Results and Publications
| Individual participant data (IPD) Intention to share | Yes |
|---|---|
| IPD sharing plan summary | Published as a supplement to the results publication |
| IPD sharing plan | De-identified individual participant data that underlie the results reported in publications arising from this study (including salivary melatonin concentrations, pupil response measures, and relevant demographic and experimental variables) will be made available. Data will be shared following or as part of publication of the primary study results, after removal of all direct and indirect identifiers, in accordance with applicable data protection regulations. Supporting documentation, including the study protocol and analysis code, will also be made available. |
Study outputs
| Output type | Details | Date created | Date added | Peer reviewed? | Patient-facing? |
|---|---|---|---|---|---|
| Protocol (other) | 09/01/2026 | No | No |
Editorial Notes
09/01/2026: Study's existence confirmed by the TUM Ethics Committee.
