Women in the military have a tremendous amount on their plate: Besides risking their lives in combat, they have to contend with post-traumatic stress disorder, exposure to hazardous chemicals, and even sexual assault and harassment by fellow soldiers or officers. But research shows they may have something even more disturbing to cope with: an increased risk of breast cancer.

Military women do have a slightly higher breast cancer risk than other women in the same age group, according to a 2009 Walter Reed Army Medical Center study. Researchers found that white women in the armed forces face a 19% higher risk and black women have a 37% higher risk. Among 100,000 people, that's the difference between 30.6 and 36.4 cases of breast cancer in white women and 33.4 and 45.8 in black women.

And while some believe this increase may be due to more rigorous breast cancer screenings, “there’s no doubt that there’s a link,” says Richard Clapp, Dsc, MPH, professor emeritus of environmental health at Boston University who has consulted with the Centers for Disease Control and Prevention (CDC) on military breast cancer issues. A few possible factors:

Chemical exposure

Women in the military are more often employed in jobs such as auto mechanic or motor transport operator where they’re exposed to volatile organic compounds (VOCs), potentially toxic chemicals that have been shown to stimulate breast cancer cell growth in laboratory animals, Clapp says. In fact, Army women exposed to at least one VOC had a 48% increased risk of breast cancer, according to a 2005 study done at the Navy Environmental Health Center in Portsmouth, Virginia.

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Shift work

Military members often work nights or work in a pattern called rotating shifts that disrupts the day/night rhythm: “It suppresses melatonin, which we suspect makes it harder for your body to fight off potentially cancerous changes in cells,” Clapp explains. Female military workers who had worked the night shift were 40% more likely to develop breast cancer in a 2012 Danish study.

Contaminated military bases

In the early 1980s, it was discovered that two water supply systems at Marine Corps Base Camp LeJeune in North Carolina were contaminated with VOCs such as the metal degreaser trichloroethylene and the dry cleaning agent perchloroethylene. Government data later found that workers stationed there had higher mortality rates from all types of cancer compared to workers at another military base. Not only were there higher rates of fatal breast cancer in women, the CDC is currently investigating whether contamination at Camp LeJeune caused unusually high rates of breast cancer in men.

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Greater birth control pill use

A 2010 study published in the Journal of Women's Health found that 34% of women in the military use oral contraceptives, compared to 29% of the general population. The authors speculated that it might be one of the reasons military women are more at risk for developing breast cancer—studies have suggested that recent or current use of hormonal birth control pills can increase risk in premenopausal women. (A recent study in the journal Cancer Research found that increasingly popular low-dose estrogen pills were not associated with a higher breast cancer risk, while high-dose estrogen pills were.)

What to do

While groups like the American Cancer Society recommend women get annual mammograms starting at age 40, if you’ve served in the military talk to your doctor about beginning screening earlier—and possibly having it done more frequently, suggests Clapp. (The Veterans Health Administration has been working to expand breast cancer screening services for female veterans.) You may also want to discuss with your doctor whether or not you’d be a good candidate for an MRI; research suggests combining MRI and mammogram detects more cancers in high-risk women than mammography alone.

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