We all hate air pollution, right? It gets into our lungs, throats and noses, and makes cities from Beijing to Paris look like a badly ventilated bathroom after a long shower.
But there’s another pollutant that could also be making us ill: light.
A new study released by the Royal Society surveys research which seems to show that nighttime light can contribute to “breast and prostate cancers, obesity, diabetes and depression”. These conditions become more prevalent as cities modernise and, as a result, electrify – but is light pollution really the explanation?
It’s certainly unhealthy. All species develop something called a “circadian rhythm” based on 24-hour cycles of light and dark. Yet most humans now work indoors during the day, where light isn’t usually bright enough to be registered by our bodies as daylight. And at night, light pollution from streetlights, cars, and all the other night-time activities in cities and towns, convince our bodies that it isn’t night, either. We rarely experience what researchers call “true dark”.
According to the study’s authors, this disruption of our daily cycles can affect our “Core body temperature, hormone regulation and release, and patterns of gene expression through the body”.
Take Melatonin, a hormone which regulates our sleep patterns and also acts as an antioxidant. Our bodies produce it at night, but even low levels of light can suppress it – and reduced levels of melatonin have been linked to certain forms of cancer.
Of course, while we’re asleep, low levels of light don’t penetrate to our retinas – so someone with light-blocking curtains and a solid eight or nine hours of sleep a night may well have developed a stable circadian cycle. But even waking up occasionally in a room permeated by light pollution, or turning on a bathroom light, can disrupt melatonin production. Here’s a chart showing a normal melatonin production profile, versus the profile of a jetlagged subject who sleeps during the day:
Even with the lights off, the jetlagged person’s body is registering the fact that it’s not quite dark.
As a result, the worst affected by disrupted circadian rhythms are actually shift workers: another study found that women who work night shifts have higher rates of breast cancer. And in 2007, the International Agency for Cancer Research declared that shiftwork may well be a carcinogen. Add enough floodlights and bright streetlights to our cities, though, and we might as well all be shift workers.
Obviously, we should be cautious of blaming all our urban ills on a bit of night-time light. Indeed, the researchers note that findings linking light pollution and illness so far have been “promising” rather than final. But to be truly safe, it might be worth moving to Sark.
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