Exposure to Light at Night Linked to Breast Cancer

Women who live in neighborhoods with large amounts of nighttime light are more likely to get breast cancer than those who live in areas where the nights are darker. This reinforces previous studies that exposure to too much light at night can raise the risk of breast cancer by interfering with the brain’s production of melatonin, a tumor-suppressing hormone.

A study published in the journal Chronobiology International overlaid satellite images of Earth onto a map with local statistics of breast cancer and, for comparison, lung cancer, which is caused mostly by smoking and would not be expected to be linked to light.

After adjusting for variables such as ethnic makeup, birth rate, population density and local income, researchers found that breast cancer rate in localities with average night lighting to be 37% higher than in communities with the lowest amount of light. The rate was higher by an additional 27% in areas with the highest amount of light.

Research has shown that rats raised in cages where lights are left on at night have higher cancer rates than those allowed to sleep in darkness. Epidemiological studies of nurses, flight attendants and others who work at night have found breast cancer rates 60% above normal, even when other factors such as differences in diet are accounted for. On the basis of such studies, an arm of the World Health Organization announced its decision to classify shift work as a “probable carcinogen.”

SOURCE: Lights at Night Are Linked to Breast Cancer http://www.washingtonpost.com/wp-dyn/content/article/2008/02/19/AR2008021902398.html?hpid=moreheadlines