Outdoor light at night was linked to a higher risk of breast cancer in a study published in the International Journal of Cancer.

For the study, investigators analyzed residential outdoor light at night estimated from satellite imagery in 1996 and assessed rates of breast cancer over 16 years of follow-up in 186,981 postmenopausal women.

Compared with the lowest level of exposure to outdoor light at night, the highest exposure was associated with a 10% higher risk of developing breast cancer during follow-up, after controlling for confounding factors.

"The small number of studies to investigate this question have often relied on subjective exposure data and yielded inconsistent results. We utilized an objective exposure measure--estimated outdoor light at night from satellite data," said senior author Rena Jones, PhD, MS, of the National Cancer Institute, part of the National Institutes of Health. "It will be important for future studies to accurately measure light at night exposure for individuals using a combination of objective measures, carefully designed questionnaires, and personal measurement devices."

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