A third of breast cancers can be prevented, new research says

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Maybe you're too cool to wear a pink ribbon, or too jaded to join a race "for the cure." But that doesn't mean breast-cancer events have nothing to do with you.

Fundraising organizations such as the Canadian Breast Cancer Foundation and the Breast Cancer Society of Canada not only help scientists find better treatments for cancer patients, but they also support research studies that increase scientists' understanding of how to prevent the disease. The good news is that a third of breast-cancer cases can be prevented, according to the Canadian Cancer Society.

Women can reduce their risk by avoiding smoking, radiation exposure and hormone therapy, and by maintaining a healthy weight and, if possible, choosing to breastfeed if and when they have children, the Mayo Clinic says. Newer studies suggest women can further reduce their breast-cancer risk by avoiding night shifts, limiting alcohol to less than one drink a day, and getting enough exercise to have a positive effect on breast-cancer biomarkers in the blood.

Here is the latest in breast-cancer prevention.

Minimize alcohol intake

Every extra drink increases the risk of breast cancer, says Dr. Tim Stockwell, director of the Centre for Addictions Research at the University of Victoria.

"Alcohol is a carcinogen and it's recognized by the World Health Organization as a cause of cancer of the mouth, colon, throat, esophogus and stomach," says Stockwell, who recently released a meta-analysis showing increased risk with moderate drinking. Drinking guidelines in Canada recommend no more than two drinks a day. But Stockwell says even two may be too many. After poring over 60 alcohol and breast-cancer-related studies from around the world, he concluded even women who abide by the lowest drinking guidelines have an 8.5-per-cent increased risk of breast cancer, while women who exceed the recommended guidelines have a 37-per-cent increased risk.

"There are 5,000 women in Canada who die from breast cancer each year. Looking at the size of the relationship between alcohol and breast cancer, approximately 500 can be attributed to alcohol use," Stockwell says. "In most cases of women who die of breast cancer, alcohol is just one of a whole range of risk factors. My advice is be cautious with alcohol, especially if you have a family history of breast cancer."

Avoid shift work if possible

In 2007, research from the International Agency for Research on Cancer concluded that night shift work was probably a risk factor for breast cancer, says Dr. Carolyn Gotay, a professor and Canadian Cancer Society Chair in Primary Prevention at the University of British Columbia.

The research, based on human and animal studies, showed exposure to light at night disrupts a woman's circadian rhythm and inhibits the production of melatonin, a hormone that can suppress tumour development. Night light can also suppress vitamin D, as well as contribute to behavioural dysfunction due to lack of sleep and stress from families functioning on different time schedules.

"When you don't sleep, a lot of other things don't go well with your body and your life," Gotay says.

Her colleague Dr. Paula Gordon, a clinical professor in UBC's Department of Radiology, notes that another study used satellites to determine which neighbourhoods had the most night light and then overlaid those images with a map of breast-cancer incidence. The breast-cancer rate was 37 per cent higher in the areas with the greatest amount of light, says Gordon, who adds that blind women have lower than average breast-cancer rates.

Exercise is key

"More than 100 studies have examined physical activity and breast-cancer risk," says Dr. Christine Friedenreich, scientific leader for Cancer Epidemiology and Prevention Research at Alberta Health Services, "and they've shown women who are physically active have a 20- to 25-per-cent reduced risk of breast cancer."

Even a moderate amount of physical activity (getting the heart rate up) is beneficial, Friedenreich says. "Sustained activity throughout a lifetime is probably the best, but even if you become active after menopause, exercise reduces the risk."

Friedenreich recently conducted a study that put healthy but inactive post-menopausal women on a year-long exercise program. "We then looked at how physical activity influenced the biomarkers associated with breast cancer, and found the level of those biomarkers decreased."

The question is how many minutes should women exercise a week? "Our results haven't been published yet, but 150 minutes a week does produce positive results, while 300 minutes is even more beneficial," Friedenreich says.

She also notes that women with breast cancer who continue to exercise cope better with their cancer treatments and have improved survival rates because it improves their quality of life and their fitness levels, and lessens their fatigue.

With files from Adriana Barton