Does Working The Night Shift Increase Breast Cancer Risk?

Does Working The Night Shift Increase Breast Cancer Risk?

Could night shift work be a potential breast cancer risk to women? That’s what a new study from Harvard appears to be suggesting, as outdoor light at night just might be one of the many risk factors for the disease.

As reported by the New York Daily News, the Harvard study showed that women who live in locations that have a high level of light in the nighttime have a 14 percent greater risk of developing breast cancer than those who live in areas with low levels of nighttime light. But that didn’t apply to all of the women in the study, as the only ones in the former areas with elevated breast cancer risk were those who worked night shifts and younger women who were current or former smokers.

But why do outdoor light at night and night shift work make women more susceptible to breast cancer? The New York Daily News noted that there have been previous studies that singled out the brain hormone melatonin, which regulates sleep and alertness while awake. Lower melatonin levels had previously been cited as a risk factor for breast cancer, with cigarette smoking having the capability of lowering melatonin levels, as well.

Working off the data from these previous studies, lead researcher Peter James and his colleagues tracked close to 110,000 women, all of whom were monitored as part of a long-term study of nurses that spanned from 1989 to 2013. James’ team gathered data on the nighttime light each woman might have been exposed to by taking nighttime satellite images, as well as records that confirmed whether a subject had worked the night shift or not.

According to WebMD, the researchers then isolated the top 20 percent in terms of outdoor light exposure at night and ultimately discovered that smoking and night shift work both turned nighttime exposure to outdoor lights into a breast cancer risk factor. Higher levels of outdoor light at night tended to increase the likelihood of the women developing the disease. This wasn’t the case, however, for older women and women who never smoked cigarettes.

As the study was not designed to prove causality, some experts are skeptical about nighttime outdoor lighting being a breast cancer risk factor, particularly for night shift workers.

“The findings in this study have to be taken with caution,” said Lenox Hill Hospital chief of surgical oncology Stephanie Bernik, as quoted by WebMD.

“Although circadian rhythm disruption may be a factor in increasing the risk of cancer, it could be other factors related to working at night as well.”

Bernik added that there may be other variables at play, such as the inability to eat a proper diet or get regular exercise — both known breast cancer risks — while working the night shift. She concluded that more research might be needed to fully establish a definite link between night shift work and/or outdoor lighting at night and breast cancer.

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