A long-term study found that women who are often exposed to artificial light have higher risks for breast cancer. The link between artificial light exposure and breast cancer risks was evident in some women more than others, particularly among premenopausal women with a history of smoking.

Exposure To Artificial Light

A long-term study found that women who are more often exposed to artificial light during night time have higher risks of developing breast cancer. In fact, they found that the risks of breast cancer in women subjected to such exposures are higher by as much as 14 percent.

Particularly more susceptible are women who live in areas which have high levels of outdoor lighting at night.

Comprehensive Study

Although similar studies have been done before, this is perhaps the most comprehensive one to examine the link between artificial light and breast cancer risks. As a matter of fact, the researchers studied data from nearly 110,000 women enrolled in the Nurses' Health Study II between the years of 1989 and 2013. They also studied night time satellite images of Earth, specifically in the residential addresses of each participant.

Each participant's socioeconomic and health status, as well as possible night shift work, was also considered in the study.

Smokers And Night Shift Workers

As aforementioned, risks were 14 percent higher for women with higher exposures to outdoor light compared to the women with the lowest exposures. Among the participants, 3,549 breast cancer incidences were recorded.

Interestingly, the link was found among premenopausal women and women who were past or present smokers. A strong link was also found among women who worked night shifts, suggesting that perhaps the combination of artificial light exposure at night and night shift work contribute to the risk increase.

Melatonin Disruption

This isn't the first study to review the relationship between the light exposure and breast cancer. Just like in previous studies, researchers suspect that the culprit remains to be hormone disruption brought about by exposure to light even during night time hours.

"The growing research on light at night and breast cancer is based on data suggesting that exposure to light during nighttime hours suppresses nocturnal secretion of melatonin and disrupts circadian patterns and sleep," said Peter James, assistant professor at Harvard Medical School and lead author of the study.

Melatonin is a naturally occurring hormone that is secreted by a small gland in the brain but can also be found in various food items and supplements. It is a hormone that is particularly in charge of sleep and wake cycles, which in turn affect the cell cycles of the body.

Researchers state that a possible explanation for melatonin's effects on cancer risk lies in the idea that a disruption in normal circadian patterns leads to abnormal cell division.

Not Just Humans

Interestingly, the harmful effects of artificial lighting do not just affect humans. In previous experiments, mice that were subjected to reversed light cycles were found to have more mammary tumors. What's more, a recent study also found that the productivity of bees is significantly affected in areas exposed to artificial light.

Because of these results, researchers believe that further studies are needed to uncover the effects of artificial lighting. It is also possible that its negative effects aren't just exclusive to women, especially since previous studies have also linked other forms of cancer such as prostate cancer.

The study is published in the journal Environmental Health Perspectives.

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