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Obesity and high-fat diets have long been known to be risk factors for breast cancer. But recent research is pointing to an altogether different hazard: the artificial light that shift workers—nurses, doctors, flight attendants, police officers, janitors, and supermarket stockers among them—are routinely exposed to at night. It’s just one of many occupational hazards linked to breast cancer that the Vancouver-based organization Toxic Free Canada highlights in its publication “Environmental Exposure: The CancerSmart Guide to Breast Cancer Prevention”.

“Someone’s got to shine a light on this,” Toxic Free Canada executive director Mae Burrows says of the light-at-night factor in a phone interview with the Georgia Straight. “We know the obvious connections like tobacco, but a lot of shift workers have never heard of this. We need to go there because it’s affecting women’s health.”

According to the just-released guide, exposure to light at night suppresses melatonin, a hormone that regulates the body’s circadian rhythms.

Last year, Denmark became the first country in the world to provide compensation to women whose breast cancer was related to occupational exposure to light. The decision concerned 37 women, many of them nurses and flight attendants, who had worked at least one graveyard shift a week for the previous 20 to 30 years. The exposure was found to have disrupted their natural body rhythms.

The journal Cancer Research reported in 2005 that the number of breast-cancer cells was higher in laboratory rats that were exposed to nighttime artificial light than in those that weren’t.

“This is clearly an occupational issue,” says guide author Sean Griffin in a phone call from the Toxic Free Canada office. “There seems to be a disconnect between workplace health—which is governed by industry laws and labour relations—and public health. But health in the workplace is very much connected to public health.”

Other industries, including those that require workers to be near solvents, pesticides, diesel exhaust, and low-frequency electromagnetic fields, have been shown to present cancer-related hazards. The link even exists in men: according to Toxic Free Canada’s guide—which was produced with funding from the Canadian Breast Cancer Foundation’s B.C.–Yukon branch—the incidence of breast cancer in men is on the rise, and the risk is higher in electricians and communications workers exposed to electromagnetic fields, as well as those working with gasoline.

Toxic Free Canada created the guide—which can be downloaded here—in response to the overwhelming demand for its 2004 publication “CancerSmart Consumer Guide”. People told the organization (formerly known as the Labour Environmental Alliance Society) that they wanted more information specifically related to breast cancer.

It’s no wonder the environmental link to breast cancer is such a hot topic: according to the Canadian Cancer Society, an estimated 22,700 women were diagnosed with the disease this year. It’s also the second leading cause of cancer death among women. There are 166,000 female breast-cancer survivors across the country.

Another significant risk factor for breast cancer, according to the guide, is exposure to xenoestrogens. The best-known of these endocrine-disrupting chemicals is bisphenol A, which is found in polycarbonate water bottles. An Environmental Health Perspectives study published in September found that levels of BPA in participants’ urine increased by 67 percent after just one week of using the bottles.

Other xenoestrogens include parabens, phthalates, and nonylphenol, which are found in some shampoos and cosmetics.

“Environmental Exposure” also reiterates the link between alcohol consumption and breast cancer. Ethanol, which is found in alcoholic beverages, has been classified as a known carcinogen by the International Agency for Research on Cancer. The Canadian Cancer Society states that women should limit their alcohol consumption to one drink a day or less.

Carolyn Gotay, the Canadian Cancer Society’s chair in cancer primary prevention at UBC and a member of the review committee for “Environmental Exposure”, notes that public interest in the connection between certain toxins and cancer has increased over the past decade or so as people have become more environmentally conscious. She cautions, however, that preventive measures such as eating a healthy diet and being physically active must not be overlooked.

“We need to have a balanced perspective,” says Gotay, who’s also a member of the Canadian Breast Cancer Foundation’s 2020 prevention working group, in a phone interview. “We know that not being overweight and avoiding obesity make a huge difference.”

The “precautionary principle” is a good one for people to adopt where possible, she adds. Simply put, that means reducing or eliminating your exposure to potentially carcinogenic substances even if conclusive proof is lacking.

“If there’s a possibility that something is harmful, and you can make changes without it costing your life savings or being very difficult, then why not err on the side of caution?”

Besides outlining environmental and occupational hazards related to breast cancer, Toxic Free Canada’s guide also sets out policy changes it says must be enacted in order to further protect people across the country. Among them are labelling legislation that would guarantee consumers can see what hazardous ingredients are in the products they buy, and including workers in the establishment of occupational-exposure limits for harmful substances.

“The guide allows people to be educated, to make informed personal choices, to work collectively in the workplace and for the betterment of society as a whole,” Burrows says. “The banning of cosmetic pesticides should be a no-brainer. We need to protect young children from pesticides so that when they grow up they don’t get breast cancer.”