Men who are exposed to artificial light at night have a higher risk of developing prostate cancer, according to new research by University of Haifa scientists just published in the journal Chronobiology International. The findings join previous research that has found nightly exposure to artificial light increases the risk among women of breast cancer and of nearsightedness in children. The analysis was conducted by Prof. Avraham Haim, Prof. Boris Portnov and Itai Klug of the university, together with Prof. Richard Stevens, a leading cancer epidemiologist of the University of Connecticut. International Agency for Research data from 164 countries on nightly exposure among men to artificial light and cases of prostate, lung and colorectal cancer were compared. In addition, information on illumination at night was obtained from the US Defense Department's weather satellite project. Information about the size and population density of each country, along with electricity use, socioeconomic factors, the percentage of urban residents and other factors were used to calculate the average amount of artificial light to which the population was exposed at night. In the first stage of research, it was clearly found that there was a connection between artificial illumination and electricity consumption at night and prostate cancer (but not the other types of cancer). After the researchers isolated the factor of the amount of light to which the average person was exposed at night in countries categorized as low, medium and high exposure, the researchers determined that in low-exposure countries, the rate was 66.77 prostate cancer patients per 100,000 residents; 87.11 per 100,000 residents in medium- exposure countries and 157 patients per 100,000 in high-exposure countries. Although the cause has not been proven, the researchers suggested that repression of the production of melatonin hormone in the brain and weakening of the immune system because of light's disruption at night of the biological clock - causing confusion between day and night - could be the explanations. "The findings do not mean that we have to return to the Middle Ages and turn off all the lights at night," the researchers said, but night illumination should be taken into account in the planning of a country's energy policy. They added that increasing artificial illumination at night is considered by the World Health Organization as a "source of pollution." Thus, they concluded, the Environmental Protection Ministry's call for using energy-saving fluorescent light bulbs, which bring about increased use of illumination, is problematic. "The state should encourage savings in lighting and a reduction in the amount of pollution," they said.