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Link between light at night and breast cancer

Katie Coyne23/08/2017 - 16:31

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Outdoor lights pose potential risk
Outdoor lights pose potential risk

Breast cancer risk could be increased with exposure to outdoor light, particularly for women who do night shifts.

The study in the journal Environmental Health Perspectives found that as levels of outdoor light at night increased, so did breast cancer rates.

However, the association between outdoor light at night and breast cancer was only found among premenopausal women and those who were current or past smokers.

The link was also stronger among women who worked night shifts. Authors suggested that exposure to night light and night shift work could contribute jointly to breast cancer risk perhaps due to disrupting circadian rhythm.

Previous research has shown that light exposure at night can decrease levels of melatonin, which regulates circadian cycles, and may protect against breast cancer.

Lead author Peter James, assistant professor at Harvard Medical School’s Department of Population Medicine said: ‘In our modern industrialised 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.’

Women exposed to the highest levels of outdoor night light, in the top fifth, had a 14 per cent increase in breast cancer during the study period. This was compared to women in the bottom fifth.

Health and socioeconomic factors were also factored into the results.

Almost 110,000 women were enrolled in the Nurses’ Health Study II from 1989-2013. Researchers used nighttime satellite images of participant’s residential addresses and also considered the impact of night shift work.

The authors said that further work needs to be done to confirm the findings and clarify what is happening to cause the link.


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