It’s no secret that in the past decades, we have been slowly losing sleep in adulthood. Many blame poor diet, lack of exercise and unmitigated stress. But there is another culprit that we cannot completely avoid—light pollution.
Research has validated that light pollution can indeed suppress melatonin production in humans and in animals.
Melatonin sets the internal clock. Researchers found that even the low light intensities of urban skyglow can suppress melatonin production.
Melatonin synchronizes the day-night-rhythm in animals and humans. It adjusts the circadian clocks of cells, tissues and organs, and regulates other seasonal processes like reproduction. In vertebrates, differences in light levels are detected by photoreceptors for example in the retina. At high light levels, melatonin production is suppressed. In darkness, melatonin is produced.
The sensitivity threshold for humans is 6 lux—street lighting is typically higher than that, the authors stated. Artificial light at night can disturb the nocturnal melatonin production. Within a literature review of 1,900 studies, the researchers identified 72 relevant works that fulfilled their criteria for light pollution. Based on the data, they showed that even very low illumination levels can suppress melatonin production for some vertebrate classes: in fish the threshold is 0.01 lux, in rodents 0.03 lux and in sensitive humans 6 lux; pure blue light showed much lower thresholds.
For comparison, the illumination levels at night: On a starry night, the illumination is 0.001 lux. On a full-moon night it reaches a maximum of 0.3 lux. The skyglow of a city, a form of light pollution, can reach illumination of up to 0.1 lux, and outdoor lighting on the order of 150 lux.
“The light from artificial lighting shines into the night sky, brighter with rain and snow, and is reflected by clouds and particles, which is called skyglow. “Surprisingly, the low light levels of skyglow are sufficient to suppress melatonin production in several vertebrate classes,” said lead author Dr. Maja Grubisic. “Skyglow affects large areas on a world-wide scale, as we know from satellite data,” added co-author Dr. Andreas Jechow.
The scientists unraveled several knowledge gaps: “There are no studies on melatonin and light pollution in reptiles and amphibians and no long term-studies at all. Particularly, the impacts on human health are not fully understood,” said IGB researcher Dr. Franz Hoelker, head of the study.
Reference:
Grubisic M, et al. “Light Pollution, Circadian Photoreception, and Melatonin in Vertebrates. Sustainability, 2019; 11 (22): 6400 DOI: 10.3390/su11226400
