Predicting melatonin suppression
Oliver Stefani, Participant of the Good Light Group, analysed and summarized a new scientific article on predicting melatonin suppression.
Variations in light conditions, both in terms of intensity and spectrum, are an important determinant of non-visual effects of light on people. Light is the principal synchronizer (i.e. Zeitgeber) of human circadian rhythms. Light exposure during the biological night can lead to sleep and circadian rhythms disturbances. In particular in the evening and at night, light with a high proportion of short wavelengths in the blue spectral range suppresses the secretion of the hormone melatonin. This hormone is naturally produced during the biological night and supports darkness related behaviour. The onset of melatonin production (in dim light) is a marker of the circadian rhythm in humans.
To support good health and sleep, the evening increase in the body's own hormone melatonin should be attenuated as little as possible. But how do we define little, and how long can this exposure last? What plays a bigger role: timing, duration, brightness or spectral composition of the light? The latest publication in J Pineal Research provides a first set of insights for answering this riddle.
The authors used machine learning to analyze light-induced melatonin suppression data from 29 peer-reviewed publications. The suppression of melatonin was primarily dominated by the spectral composition of the light exposure which defines the quantity melanopic EDI. The CIE uses this quantity in its recommendations on proper light at the proper time for Integrative and Human Centric Lighting applications. An exact dose, however, was not yet provided in the CIE recommendations.
The authors used a logistic model to predict the melatonin suppression response based on various characteristics of the light exposure (duration, spectral composition, pupil dilator usage etc.). The model predicts that for light exposure durations of 0.5, 1, 2, 3 and 4 hours, nocturnal melatonin secretion is reduced by 50% when the light exposure has a melanopic EDI of 600, 350, 120, 43 and 15 lx, respectively. This confirms and extends insights on the metric melanopic EDI being an important predictor of biological effects of light within integrative (human-centric) lighting applications.
As a metaphor, one could compare the melanopic EDI of our light environment to the caffeine content of a drink: a small espresso or a big cup of normal coffee provide the same dose of caffeine.
The publication and a small toolbox (see Supporting Information) can help lighting practitioners to better estimate the effect of light exposure on melatonin suppression. The publication, the toolbox and a video about it can be found in the Journal of Pineal Research here: https://onlinelibrary.wiley.com/doi/full/10.1111/jpi.12786