Date Published: 18 August 2017

Artificial outdoor lighting linked with female breast cancer risk

" In our modern industrialized society, artificial lighting is nearly ubiquitous. Our results suggest that this widespread exposure to outdoor lights during nighttime hours could represent a novel risk factor for breast cancer,"

said Peter James, now based at Harvard Medical School's Department of Population Medicine, who conducted this research in the Departments of Epidemiology and Environmental Health at Harvard Chan School.

Researchers based at the Harvard T.H. Chan School of Public Health in Boston, USA, have published the results of a long-term study which indicates that premenopausal women and women who are (or have been) smokers and who live in areas with higher levels of artificial outdoor light during the hours of natural darkness might be at higher risk of breast cancer than those living in areas without as much artificial light at night. They also reported that the correlation was strongest among women who worked night shifts, which implies that exposure to light at night and night shift work might combine to contribute to an increased breast cancer risk, possibly through mechanisms involving circadian disruption.

Previous studies have suggested that exposure to light at night might lead to decreased levels of the hormone melatonin, which can disrupt circadian rhythms, i.e. our internal "clocks" that govern sleepiness and alertness, and in turn, lead to increased breast cancer risk.

This recent study has been described as the most comprehensive to date to examine possible links between outdoor light at night and breast cancer. It considered data from almost 110,000 women enrolled in the Nurses' Health Study II from 1989-2013. The researchers also used data from satellite images of Earth taken at nighttime corresponding to the residential addresses of each study participant and considered the influence of night shift work. It also took into consideration detailed information on a variety of health and socioeconomic factors among the participants.

Overall the study revealed that the women exposed to the highest levels of outdoor light at night, specifically those in the top 20% of artificial outdoor light exposure, had an estimated 14% increased risk of breast cancer during the study period compared with the women who had the lowest 20% of exposure. In general terms, as levels of outdoor light at night increased, so did breast cancer rates.

The scientists involved in the study and who have recently reported their results and interpretations in the journal 'Environmental Health Perspectives' acknowledged that further research is needed to confirm their findings and clarify potential mechanisms. See more breast cancer in the news.

Source (or main source)Harvard School of Public Health, USA

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