Study Linking Street Lights to Cancers Flawed

A newly released study has found a link between exposure to blue light of street lights and the incidents of breast and prostate cancers. Researchers at the Barcelona Institute of Global Health and The University of Exeter in the UK conducted the study. They published the findings in the April issue of Environmental Health Perspectives.

While previous studies have concluded that shift workers are more susceptible to hormone-related breast cancer, and long-term disruption of circadian rhythm is the culprit. One of the causes primary causes of this sleep cycle disruption is the lighting.

So the link between artificial lighting at night and cancer risk is already well known. This recent study examined the use of street lights and claims to have found a link to breast and prostate cancers. Furthermore, they claim that blue light from street lights poses an increased risk compared to other colors of lights.  While they tried to equate blue light to LED street lights, they did not specifically look at which lights were LED street lights. Furthermore, as we have discussed in previous editorials, not all blue light is the same. (Ref: Coverage).

They looked at satellite images of Barcelona and Madrid in 2012 and 2013 taken with a DSLR camera that separated the images into red, blue, and green. However, the methodological issues with the study make the conclusions highly suspect.

The main portion of the study derived data from satellite photos. From these satellite photos the researchers claim to be able to estimate light levels from the street lights. The study did a good job of mitigating many of the potentially confounding variables. They took into account age, socio-economic level, body mass index among other potential factors. The researchers also surveyed the participants to get an idea of how much exposure to artificial light at night the subjects said they received.

Study Only Estimated Exposure with Satellite Images

One major issue with the study remains. They did not actually measure artificial light exposure at night for each subject and each control subject. They estimated. Furthermore, the estimate had to take into account reflected light from the ground etc. The researchers went further with this estimation method to calculate a very rough approximation of how much blue light was emitted and the subject’s exposure to blue light.

Part of the questionnaire looked at how much sleep they participants reported. During sleep, eyelids eliminate almost all light exposure. Actual measurements of sleep were also not taken.

In order to really perform such a study, the subjects would have to wear some kind of headband that measures light exposure and a wristband or have installed sensors that measure sleeping and even sleep stages such as REM. This way they could get a relatively accurate estimate of light exposure during the night.

Overall the study was a good exploratory effort, and it raised enough important questions. So, they should qualify for grant money for a more extensive study with exposure measurements, not just estimates.


Garcia-Saenz, A. , Sánchez de Miguel, A., Espinosa, A., et al. 2018. Evaluating the Association between Artificial Light-at-Night Exposure and Breast and Prostate Cancer Risk in Spain (MCC-Spain Study), Environmental Health Perspectives, April 2018, volume 126, issue 4. https://doi.org/10.1289/EHP1837

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