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Going to the loo at night won’t give you cancer – but it could be a warning sign

by Henry Scowcroft | Analysis

20 April 2010

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A picture of a toilet

Turning the light on won't give you cancer

Last week, The Daily Mail reported that ‘simply turning on a light at night for a few seconds to go to the toilet can cause changes that might lead to cancer’.

This might seem a far fetched link – and it is.

The researchers, based in Leicester and Israel, were studying the effects of interrupting animals’ sleep with a pulse of light lasting about an hour, on their body clocks, or ‘circadian rhythms’. They were particularly interested in how this affected rates of cell division in the animal’s brains.

They didn’t look at the effects of night time light on people, nor on cancer risk.

The University of Leicester has written an excellent commentary on the research, and the way it was reported, on its news blog. Here are a few excerpts, but its worth clicking through to read the full article:

What the researchers did was examine the connection between the circadian clock – the biofeedback mechanism which animals and plants use to regulate their physiology on a 24-hour cycle – and cell division, which is also cyclical – in mice.

During the dark period, the mice were exposed to what is described as a ‘pulse’ of  light – but pulse in this sense means a one hour exposure of bright light, not flicking a switch on and off. For different groups of mice, the pulse came at different times during the ‘night’.

Among many genes which showed changes in their activity were a group that are important for regulating the cell cycle.

Nowhere in their paper, which is published in the journal Cancer Genetics and Cytogenetics, do they mention trips to the toilet or anything even vaguely similar.

The blog post goes on to point out that there are other risks associated with going to the loo at night – namely falling over things if you DON’T put the light on.

But there’s a final, somewhat more serious point we’d like to make about going to the loo at night.

Turning the light on won’t cause cancer. But if you’re an older man and notice you find you’re having to go to the loo more than usual – especially at night – then go and see your GP and get checked out.

It’s probably nothing to worry about, but it could be an early sign that not everything’s quite right with your prostate.



Ben-Shlomo, R., & Kyriacou, C. (2010). Light pulses administered during the circadian dark phase alter expression of cell cycle associated transcripts in mouse brain Cancer Genetics and Cytogenetics, 197 (1), 65-70 DOI: 10.1016/j.cancergencyto.2009.11.003