Exposure to light at night is the most powerful factor in breast cancer besides genetic defects, according to a new University of Haifa study.

Although one can’t easily move to a dark neighborhood, stop using computers and watching TV late at night, or refuse to do shift work, it is advisable to close the shutters when you go to bed, wear eye shades if you can’t darken the bedroom, avoid night lights and lower lights in working environments after sunset.

These recommendations come from new Israeli research just published in Chronobiology International.

Women who live in neighborhoods and streets with strong outdoor lighting at night are more likely to contract breast cancer than those who have minimal nocturnal lighting, according to the research performed by Prof. Avraham Haim, a chronobiologist and expert in evolutionary and environmental biology at the University of Haifa; Itai Kloog, a doctoral student in the natural resources and environmental management department; and Prof. Boris Portnov.

There is also some unpublished evidence that men in well-lit surroundings are at higher risk for prostate cancer, but there was no link between excess light at night and lung cancer, which is caused almost exclusively by smoking.

Kloog, Haim and Portnov overlaid satellite images produced by NASA with geographical data on breast cancer from Israel’s National Cancer Registry. They also processed questionnaires filled out by 100 women with breast cancer and 100 healthy women about a wide variety of socioeconomic, environmental, genetic and other factors and their exposure to light at night. They found that the breast cancer rate in neighborhoods with average night lighting was 37 percent higher than in those with the darkest streets, while the rate was an additional 27% higher in areas with the highest amount of light.

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