Countries with the highest levels of artificial light at night also have the highest rates of prostate cancer, according to a new study by researchers at the University of Haifa.
This discovery joins the findings of a previous study by the same researchers that found a connection between exposure to artificial light at night and the incidence of breast cancer.
The study, conducted by Prof. Abraham Haim, Prof. Boris A. Portnov, and Itai Kloog of the University of Haifa together with Prof. Richard Stevens of the University of Connecticut, USA, was intended to examine the influence of various factors - including the amount of artificial light at night - on the incidence of three types of cancer: prostate, lung, and of the large intestine, in men around the world.
Data was collected from a database of the International Agency for Research on Cancer, on the incidence of these types of cancer in men in 164 countries.
Data on the levels of lighting at night were gathered from DMSP (Defense Meteorological Satellite Program) satellite images.
The nighttime illumination data were adjusted by the geographic distribution of the population of the country, in order to reach an accurate measure of "the amount of artificial light per night per person."
The researchers also examined additional factors, such as electricity consumption, percentage of urban population, socio-economic status, and other variables.
At the very first stage of the study, it already became clear that there is a marked link between the incidence of prostate cancer and levels of nighttime artificial illumination and electricity consumption.
Next, the researchers isolated the "amount of artificial light at night per person" variable in order to examine its particular effect.
The countries were divided into three groups for this stage of the study: those with little exposure to lighting at night; those with medium exposure; and those with high exposure.
The results demonstrated that the incidence of prostate cancer in those countries with low exposure was 66.77 prostate cancer patients to 100,000 inhabitants.
An increase of 30 percent was found in those countries with medium exposure: 87.11 patients per 100,000 inhabitants. The countries with the highest level of exposure to artificial light at night demonstrated a jump of 80 percent: 157 patients per 100,000 inhabitants.
The study was published in Chronobiology International in 2008.