Is light pollution making us sick?

Image: Mike Knell via Flickr.

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.


CityMetric is now City Monitor! Come see us at our new home

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CityMetric is now City Monitor, a name that reflects both a ramping up of our ambitions as well as our membership in a network of like-minded publications from New Statesman Media Group. Our new site is now live in beta, so please visit us there going forward. Here’s what CityMetric readers should know about this exciting transition.  

Regular CityMetric readers may have already noticed a few changes around here since the spring. CityMetric’s beloved founding editor, Jonn Elledge, has moved on to some new adventures, and a new team has formed to take the site into the future. It’s led by yours truly – I’m Sommer Mathis, the editor-in-chief of City Monitor. Hello!

My background includes having served as the founding editor of CityLab, editor-in-chief of Atlas Obscura, and editor-in-chief of DCist, a local news publication in the District of Columbia. I’ve been reporting on and writing about cities in one way or another for the past 15 years. To me, there is no more important story in the world right now than how cities are changing and adapting to an increasingly challenging global landscape. The majority of the world’s population lives in cities, and if we’re ever going to be able to tackle the most pressing issues currently facing our planet – the climate emergency, rising inequality, the Covid-19 pandemic ­­­– cities are going to have to lead the way.

That’s why City Monitor is now a global publication dedicated to the future of cities everywhere – not just in the UK (nor for that matter just in the US, where I live). Our mission is to help our readers, many of whom are in leadership positions around the globe, navigate how cities are changing and discover what’s next in the world of urban policy. We’ll do that through original reporting, expert opinion and most crucially, a data-driven approach that emphasises evidence and rigorous analysis. We want to arm local decision-makers and those they work in concert with – whether that’s elected officials, bureaucratic leaders, policy advocates, neighbourhood activists, academics and researchers, entrepreneurs, or plain-old engaged citizens – with real insights and potential answers to tough problems. Subjects we cover include transportation, infrastructure, housing, urban design, public safety, the environment, the economy, and much more.

The City Monitor team is made up of some of the most experienced urban policy journalists in the world. Our managing editor is Adam Sneed, also a CityLab alum where he served as a senior associate editor. Before that he was a technology reporter at Politico. Allison Arieff is City Monitor’s senior editor. She was previously editorial director of the urban planning and policy think tank SPUR, as well as a contributing columnist for The New York Times. Staff writer Jake Blumgart most recently covered development, housing and politics for WHYY, the local public radio station in Philadelphia. And our data reporter is Alexandra Kanik, whose previous roles include data reporting for Louisville Public Media in Kentucky and PublicSource in Pittsburgh, Pennsylvania.

Our team will continue to grow in the coming weeks, and we’ll also be collaborating closely with our editorial colleagues across New Statesman Media Group. In fact, we’re launching a whole network of new publications, covering topics such as the clean energy transition, foreign direct investment, technology, banks and more. Many of these sectors will frequently overlap with our cities coverage, and a key part of our plan is make the most of the expertise that all of these newsrooms combined will bring to bear on our journalism.

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As for CityMetric, some of its archives have already been moved over to the new website, and the rest will follow not long after. If you’re looking for a favourite piece from CityMetric’s past, for a time you’ll still be able to find it here, but before long the whole archive will move over to City Monitor.

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I want to thank and congratulate Jonn Elledge on a brilliant run. Everything we do from here on out will be building on the legacy of his work, and the community that he built here at CityMetric. Cheers, Jonn!

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Sommer Mathis is editor-in-chief of City Monitor.