Sex-related and hormone-related differences in non-visual responses to light exposure

Scope.
This is a comparison of published research studies (n=11) investigating sex and hormone-related differences in non-visual effects of light. Specifically, research studies investigating the following classes of non-visual effects of light were included:
1. Neuroendocrine (melatonin suppression)
2. Circadian (phase shift)
3. Pupillary (pupillary light reflex)
4. Cognitive (vigilant attention and alertness).

Identification of articles.
Articles were identified through systematic searches on Google Scholar, PubMed and Web of Science. The search words included: “sex differences in non-visual effects”, “menstrual influences in non-visual effects”, and “hormone-related differences in non-visual effects”.

Data extraction scheme.
The comparison is based on properties inspired by the ENLIGHT Checklist for reporting light characteristics in studies investigating non-visual effects of light (see Spitschan et al., 2023 in Data sources). Where possible, properties matching the ENLIGHT Checklist categories were used and additional properties were added to capture key information and facilitate comparisons. Overall, the data extraction scheme was used:
1. Comparison descriptors (n=8), i.e. core properties enabling a meaningful comparison between studies (research question, non-visual effect investigated, original study where data was collected, prospective/retrospective analysis, outcome measures: assessment, outcome measures: derived metrics, data processing/analysis notes, results)
2. Participant-level characteristics (n=6; plc01: sample size and age, plc02: ocular health and functioning, plc03: pupil size and/or dilation, plc04: reproductive health, plc05: menstrual phase coding, plc06: distinction between sex and gender)
3. Context-level characteristics (n=2; clc01: season of data collection and clc02: geographical location)
4. Study-level characteristics (n=6; slc01: general study design, slc02: timeline of the experiment (total), slc03: pre-laboratory sleep-wake behaviour, slc04: start point of in-laboratory protocol, slc05: in-laboratory experimental protocol, slc06: additional visual graphic)
5. Light-exposure level characteristics (n=9; lec01: light exposure conditions, lec02: light source type, lec03: light source location, lec04: manufacturer of light source, lec05: light level characteristics, lec06: viewing distance to stimulus, lec07: instructions for gaze during exposure, lec08: measurement details for illuminance, lec09: manufacturer of measuring instrument).

Notes on included studies.
Among the eleven studies included, the two studies from Parry et al. (1997) represent the same paper. However, since the paper comprises two different research studies, each related to a different non-visual effect of light, this single paper was entered as two separate contributions to facilitate the readability of the comparison.