Can shifting body clocks cause cancer?

Contributing Columnist

Time rules life.  Human body clocks are powerful. Disrupt them and people feel worse – and often get sick.   Shiftworkers know this: they experience more heart disease, strokes, ulcers and an earlier grave.  For years, the World Health Organization has talked of shift work as a possible carcinogen.  Yet it’s hard to prove in humans.  The people who do shift work are different from those who don’t.  Probably in part because of body clock disruptions, they engage in behaviors – eating more, smoking more – that make inference more difficult.

So a group in the Netherlands attempted to find out a different way – using animals highly prone to breast cancer.


What Did They Do?

They took specially bred mice, with a high propensity to develop  breast cancer, and then put them through different “shifts” every week.  Mice are generally active in the dark and sleep during the day.  The experimenters shifted their clocks week by week, reversing night and day alternatively.


What Happened?

The mice developed breast cancers.  Those placed on shifts developed them earlier – about 17 earlier in their lifespan.  Tumor growth was faster. Like human shift workers, they also gained weight.   Even when given the same amounts of food, the “shifted” mice weighed 20% more.


Why Did This Happen?

The researchers were greatly interested in potential mechanisms – why would clock shifts make for faster tumor growth?  They tried to look at five different mechanisms: 1. Internal desynchronization – fouled up, less than optimally functioning clocks 2. Melatonin suppression – some studies argue melatonin can play a role in prevening cancer induction 3. Vitamin D – the vitamin which is also a hormone is on most people’s lists these days for major biological effects 4. Sleep disruption – did getting less and different sleep make a difference? 5. Lifestyle disturbance – when night becomes day and day becomes night, do animals do the same stuff they would otherwise do?

Disentangling these variables is not easy.  Yet it is particularly difficult in people.  People do not enjoy living in heavily controlled environments.  Mice are a lot more malleable.

There were surprises. Despite having radically altered clocks, the mice slept more than on average.  It was as if disrupting clocks meant they needed more recovery time – which they got. Humans generally do not have that luxury – shiftworkers generally live with non-shifters, and try to adjust their sleep patterns to their social kin.  Still, the mice’s sleep was very different from normal. And at least at first glance, vitamin D did not seem to have much to do with the picture.  Ditto melatonin levels, highly disrupted for sure, but adapting over time.

What really seemed more statistically important in provoking tumor growth was disrupted clocks – and disrupted sleep.


So A Bunch of Mice Have More Tumors.  Why Should I Care?

Because it can affect you – in lots of ways.

First off, it’s not the only piece of evidence that shifting body clocks can provoke cancer.  Far from it.  The epidemiologic evidence has been growing for decades.  Messing up your inner clocks is not healthy.

Second, while people are upset by body clock disruption effects like obesity, ulcers, heart attack and strokes, they really get scared by cancer.  Since about a quarter of workers do shift work – more if you consider all the commute time involved in today’s work force of part timers doing 15 hours here, 20 hours there – calling shift work a carcinogen should change the economic and political debate.

Plus breast cancer is sadly very common.  About one in eight women now receive that diagnosis.   No wonder there are calls today for women to avoid jobs like flight attendant – with its crazy hours and cosmic ray exposure – if there is any family history of breast cancer.

But the biggest issue may be that with the internet, social media lifestyle of today, normal, regular body clock lifestyles mean less to people than ever.  Teens routinely take their cellphones into bed.  Routinely, they answer texts and calls throughout the night.  College students refuse morning classes, having been up with “more entertaining” engagements through the night.

And often the American worker of today is loathe to refuse a boss’s call in the middle of the night.  The 24-7 work cycle is here; so inow s the 24-7 social cycle.

That such lifestyles increase weight, make people look less attractive, and set them up for more colds, heart attacks and strokes, does not appear to have much currency in present social media.  If your best Facebook friends text you at 3 AM because something really cool happened, you text back.

But people are scared of cancer.  If they recognize that disrupting body clocks – and sleep – can provoke tumors, they may think again.


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