Patient Education

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Cancer Awareness

October 2013

Work the Night Shift? You May Be More Prone to Breast Cancer

Humans are naturally diurnal—we prefer to be active during the day and sleep at night. Working the night shift disrupts this normal pattern. The result: a potential host of health problems, including insomnia, heart disease, and stomach illnesses. Recent research implies you can also add breast cancer to that list.

The latest evidence

Scientists have been exploring for years why women develop breast cancer. Through ongoing research, they've pinpointed several factors that can increase your chances for the disease. For instance, growing older makes you more susceptible to breast cancer. So, too, does a family history of it.

Unlike these well-established links, experts have only recently noted a possible connection between breast cancer and working the night shift. In fact, less than a decade ago the International Agency for Research on Cancer declared that shift work may cause cancer. Research isn't always conclusive on the issue, but evidence may be mounting.

One recent study followed for an average of 12 years more than 4,000 women who worked either days or nights. Researchers asked participants about their job history and compared it with health records. They found that women who clocked in at night were twice as likely to develop breast cancer.

In the journal Occupational and Environmental Medicine, scientists drew a similar conclusion. But time on the job mattered. Only women who worked nights for more than 30 years had double the risk for breast cancer.

Day and night

Why might working nights lead to a breast cancer diagnosis? Experts suspect melatonin—a hormone produced by the pineal gland in your brain. Melatonin helps regulate body cycles, mood, sleep, and reproduction. Its antioxidant properties may also stave off the growth of cancer cells.

Your body makes most of its melatonin at night. When you are exposed to light, production decreases. In a recent study, people who worked the night shift had lower levels of melatonin in their urine compared with those who worked days. Their bodies also didn't make as much of the hormone overall, even on days off when they were able to sleep normally. This drop in melatonin may allow breast cancer to grow.

Fending Off Breast Cancer

Even if you work the night shift or have other risks for breast cancer, it isn’t guaranteed that you will develop the disease. You can do a lot to prevent it. Follow these steps:

  • Schedule regular mammograms and breast exams. Talk with your doctor to see how often you should be tested and how young you should start.

  • Think low-fat and high-fiber. Include 2-1/2 cups or more of fruits and vegetables per day. A healthy, nutritious diet may help decrease the risk for several cancers.

  • Maintain a healthy weight. A recommended range is a body mass index (BMI) of 18.5 to 24.9.

  • Exercise. Regular exercise will help keep your weight down and has many other health benefits.

  • Limit alcohol. If you choose to drink, stop at one drink a day (or less).

October is National Breast Cancer Awareness Month. Discover more about risk factors for the disease here.

Online Resources

American Cancer Society – Breast Cancer

National Cancer Institute – Breast Cancer

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