I expressed the first serious concern about the potential health consequences of electric light at night 30 years ago, when I asked whether over-lighting might increase the risk of breast cancer. It was during the 1980s, just as researchers were finding that a fatty Western diet might not much alter the breast-cancer risk in individuals, that a friend from the Fred Hutchinson Cancer Research Center in Seattle pointed me to research on the impact of melatonin. Lowered levels of melatonin (an effect of over-lighting) had been traced to heightened levels of oestrogen (at least in rodents), a clear breast-cancer risk factor when fatty diets were not. Later evidence has shown that women who work the night shift are at higher breast-cancer risk. Evidence suggests that circadian disruption from over-lighting the night could be related to risk of obesity and depression as well. In fact, it might be that virtually all aspects of health and wellbeing are dependent to one extent or another on a synchronized circadian rhythmicity, with a natural cycle of bright days and dark nights.
This makes me very happy about preference for a firelight level of light at night.
Putting a finer point on the risk is ‘The New World Atlas of Artificial Night Sky Brightness’, published in 2016. The atlas uses data from NASA’s Suomi National Polar-orbiting Partnership satellite to estimate skyglow across the globe. The images in the atlas are either dazzling or horrifying, depending on how you look at it. In its colored maps of cities and countries, using brighter colors to show greater skyglow, Europe and North America appear ablaze. According to the atlas, the Milky Way cannot be seen at night by one-third of humans. In Europe, it’s not visible to 60 percent of people, and in North America, it’s a whopping 80 percent.
That would be me.