Study title: Evening home lighting adversely impacts the circadian system and sleep Nature, Nov 2020
Overview of the study:
Quick background: Melatonin is a hormone that the body produces at night, and it is an integral part of our circadian rhythm. Levels rise at night when it is dark, and melatonin is suppressed to a lower level during the day through bright light exposure. Melatonin and the body’s natural circadian rhythm are essential to health and wellbeing — and messing with this system with electric lighting at night increases the risk of almost all modern chronic diseases (diabetes, depression, heart disease, dementia, ADHD, some cancers, etc.). (Read more about melatonin and disease risk)
In this new study, participants wore eye-level light monitoring devices daily to evaluate the brightness and wavelength of light exposure in the evenings and night. The researchers monitored melatonin production and sleep quality.
Overall, the results showed that light exposure in the blue wavelengths (which suppress melatonin) affected sleep quality and time to fall asleep for the first 90 minutes after bedtime. The researchers adjusted for age, sex, average bedtime, deviation from average bedtime, chronotoype, insomnia scores, and sleep quality index. After all the adjustments, the relationship still held true between brighter light in the blue wavelengths causing poor sleep efficiency and decreased slow-wave sleep.
The study results showed that there is a huge (50-fold) individual variance in the effect of light on the suppression of melatonin. For some people, exposure to home lighting in the evenings suppresses melatonin a lot (up to 87%). But other people had little melatonin suppression.
On average, melatonin was suppressed by 50% when exposed to average home lighting in the evening.
What I found most interesting was the differences in melatonin suppression due to the different types of lighting in the home. Incandescent bulbs, which are being phased out in order to save energy, don’t have as big of an effect on melatonin. But the new LED bulbs, especially the ones made for ‘white light’, have a large effect on melatonin suppression. And fluorescent bulbs also had a big effect on melatonin suppression.