Turning on the light to go to the toilet does not give you cancer
Readers of yesterday’s Daily Mail will have seen a story, Cancer danger of that night-time trip to the toilet, citing research by Professor Charalambos Kyriacou from our Department of Genetics and Dr Rachel Ben-Shlomo from the University of Haifa.
The article begins: “Simply turning on a light at night for a few seconds to go to the toilet can cause changes that might lead to cancer, scientists claim.” In fact, neither Professor Kyriacou nor Dr Ben-Shlomo suggest anything of the sort.
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.
It has recently been demonstrated that there is a connection between the two cycles, and of course cancer is, essentially, unregulated cell division. So Professor Kyriacou and Dr Ben-Shlomo placed 44 mice (22 experimental subjects, 22 controls) into an environment of 12 hours of light then 12 hours of darkness.
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’.
RNA was then extracted from the animals’ brains in order to examine which genes had been activated or inactivated by the light pulse. Among many genes which showed changes in their activity were a group that are important for regulating the cell cycle.
It has been demonstrated in the past that cancer levels among shift workers are slightly higher than in the general population. Professor Kyriacou and Dr Ben-Shlomo suggest in their conclusion, that the chronic exposure of shift workers to extended light schedules during what should be their ‘night’, may also misregulate these cell cycle genes, and could conceivably contribute to the elevated levels of tumours seen in this population.
But 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. That is entirely an invention of the Daily Mail.
(For what it’s worth, if you get up in the night to go to the loo, you’re probably best using a dim night-light for purely practical reasons. But that’s all to do with the rods and cones in your eye – nothing to do with cancer and nothing to do with this research. Also, if you don’t use some sort of illumination, you might slip and break your neck - this might be a particular problem with males!)