Does the light from the streetlights cause cancer? | Science

Does the light from the streetlights cause cancer? | Science

Thus raised the answer is no, but it is also true that there is much to talk about here. It is almost certain that the question comes from a series of studies that have been done since 2008 and that link urban areas with more night light with an increased risk of suffering from two types of cancer: breast and prostate. What the researchers did was measure the light reflected in the sky captured by the satellites and once they identified the most enlightened cities, they checked if there was some kind of association with an increase in the incidence of these cancers, breast and prostate, which are those that, in principle, would be linked with greater exposure to night light. The study authors found that there was an association between increased lighting and increased risk. The problem with these studies, and that is a real problem, is that they do not detect what light each individual receives, but what is reflected in the sky and does not necessarily coincide with that to which each one is exposed in its home.

What is known is that night-light causes the body to produce less of a hormone called melatonin

We must also bear in mind that the fact of linking the night light with cancer is somewhat controversial, it can not be said that way. What is known is that night-light causes the body to produce less of a hormone called melatonin. And we also know that this lack of melatonin alters the circadian system. You should know that the circadian system has a biological clock that is in our brain and is evolutionarily prepared to detect the alternation between light and dark, between day and night. We also know, thanks to epidemiological studies, that alterations in our circadian system are linked to a series of diseases such as metabolic syndrome and other cognitive and affective disorders. It is known, for example, that people who work shifts and have altered their circadian system are more prone to this type of disease.

In 2008, the World Health Organization published a report that said circadian disruption, which includes light and other aspects, is potentially carcinogenic to humans and included in group 2A. Group 2A includes factors that do not show experimental evidence in humans with the appearance of cancer but that the relationship is associative, not causal. That is, the two things seem to go together but we can not show that one leads to the other. In experimental animals, the evidence is sufficient to say it, but not in the human case.

Lleida at night.
Lleida at night.

You should also know that this link between night light and cancer risk does not refer only to the light of the streetlights, but to any light outside the hour. By introducing the electric light at night, we are sending a conflicting signal to our biological clock and altering the signal of that clock in our brain is not good. But it does not have to be the light of a lamppost, there can also be bad habits like having at night very white lights, very cold, since the circadian system is especially sensitive to lights with more bluish component and there are lights that we perceive as white that are really cold lights and have a lot of blue. That light that would be good during the day, at night is much more effective in inhibiting the secretion of melatonin and therefore we should avoid it.

One of the scientists most involved in these studies on night-light, Stephen Pauley, said that he became aware of the problem of light pollution because he could read the newspaper in his room without turning on the light. And then he started asking himself questions.

Alterations in our circadian system are linked to a series of diseases such as metabolic syndrome and other cognitive and affective disorders

In any case, a good advice is to darken the house at night as much as possible. There are times when we say it at conferences people smile and that "day must be day and night, night". The day must have light, more noise and higher temperature and the night must be cooler, to allow the dream, it must be dark and it must be calmer with respect to the noises. Preparing the dream is something that we have lost. We have bad habits like watching television until very late or being connected to the computer that in many cases also emits this blue light. You can not turn off the computer, snap your fingers and fall asleep three seconds later, when the time comes to sleep you need a time to relax, lower the intensity of the light, more orange lights …

But just as you have to be clear that because you have a lamp next to your window you will not have cancer the next month, it is also important that we all have clear that night should be night and there should be legislation to reduce that intrusive light. One thing is that we can not establish a causal relationship between night light and the highest risk of cancer but we can say with forcefulness that the night light is not beneficial.

María de los Ángeles Rol de Lama is a professor of Physiology at the University of Murcia. Co-director of the Chronobiology Laboratory (Cronolab).

Question done via email by Ada García

Coordination and writing: Victoria Toro

We respond is a weekly scientific office, sponsored by the Esteve Foundation, which answers readers' doubts about science and technology. They are scientists and technologists, members of AMIT (Association of Women Researchers and Technologists), those that answer those doubts. Send your questions to us or on Twitter # we answer


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