Systematic review of light exposure impact on human circadian rhythm.
Level 1 - systematic review of randomized trials
Systematic review of experimental and observational human studies on light exposure and circadian markers.
PubMed 30311830 · doi:10.1080/07420528.2018.1527773
What was done
A systematic review was conducted to evaluate the effects of light exposure on human circadian markers (melatonin secretion and rapid-eye-movement sleep). Searches yielded 128 articles (122 reporting on melatonin, 13 on REM sleep). Studies were categorized into controlled experimental exposures (101 reports) and prevailing ambient light conditions (21 reports). A secondary synthesis was restricted to 15 qualified studies (13 melatonin, 2 REM sleep) that met quality criteria of at least 20 subjects and precise reporting of light parameters (spectrum/wavelength and illuminance/irradiance/photon density).
What was found
A two-hour evening exposure to blue light (460 nm) suppressed melatonin, with peak suppression occurring at the shortest wavelength evaluated (424 nm, violet). Melatonin concentrations recovered within 15 minutes after light cessation. Melatonin secretion and light-induced suppression declined with age, but light-induced circadian phase advance was preserved. Circadian phase resetting occurred with evening, nighttime, and morning light, including intermittent exposures and long wavelengths (631 nm, red). Exposure to low light levels (5 to 10 lux) during sleep with eyes closed also produced a circadian response.
Why it matters
This synthesis provides detailed optical parameter thresholds (wavelength, timing, and lux levels) for human circadian disruption, supporting the integration of light pollution metrics into environmental life-cycle assessments.
Limits
The vast majority of existing literature relies on small cohorts (39 of 128 studies evaluated 10 or fewer subjects), leaving only 15 studies with at least 20 participants. Most participants were young adults in their 20s or 30s, leaving children and older adults heavily underrepresented. The abstract provides no pooled effect sizes or meta-analytic confidence intervals.
Cited by
- supports Exposure to even small amounts of bright artificial light between approximately 9:30 p.m. and 4:00 a.m. suppresses melatonin secretion and impairs sleep quality.