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Sometimes Tina Mitsis, 28, feels like a walking time bomb. "Both my mother and grandmother have or have had breast cancer," says Tina, a lawyer in New York City. But rather than live in fear, she's taking action to outsmart the disease. "I'm fit, I'm at a healthy weight, and I intend to stay that way," she says. Tina does cardio workouts at the gym two to three times a week, she walks 40 minutes a day, and she eats plenty of fruits and vegetables. So far, so good: For the past two years her quarterly breast exams have been clean.
Tina has discovered what more and more researchers are calling one of the secrets of preventing breast cancer: maintaining a healthy weight. The latest research shows that being overweight or obese significantly raises a woman's chances of getting the disease -- and it's often a far bigger factor than genetics. "Women think breast cancer is mainly related to family history," says Melinda Irwin, PhD, associate professor of epidemiology and public health at Yale School of Medicine. "But in truth, only about 10 percent of cases are. That means 90 percent of breast cancer may be caused by environmental or lifestyle factors like weight."
Packing extra pounds is one of the biggest risks for many types of cancer. In a groundbreaking study published several years ago in the New England Journal of Medicine, women who weighed the most died of cancer at a 62 percent higher rate than those who were slimmer. The researchers blamed excess weight for up to half of all deaths from breast cancer alone. "The scary thing is that even as more and more research shows a link between weight and cancer, women are becoming heavier and less active," Irwin says. She and other experts worry that this could lead to a rise in cancer cases down the road.
Yet for all the dire warnings, women aren't getting the message. Only 8 percent of people in the United States realize that being heavy increases cancer risk, reports the American Cancer Society; 92 percent have no idea. One reason for this: Doctors rarely discuss weight during the typical office visit. Just 11 percent of overweight patients received diet counseling from their MDs, concluded a study by Robert Wood Johnson Medical School in New Brunswick, New Jersey. "Most doctors find dealing with weight frustrating," says Jeanne Ferrante, MD, a researcher at the school who did a follow-up study on physician attitudes. "That's partly because a lot of patients don't like to talk about it. But doctors also have negative attitudes." In the study, 78 percent of doctors felt obese people didn't have enough discipline to lose weight, and 52 percent felt they weren't motivated enough.
Not only that, obese women are more likely to skip cancer screenings such as mammograms, according to research at the University of California, Berkeley. "It's a double-edged sword," Irwin says. "Women who are heavy or who gain weight up their cancer risk, but they also become less likely to get the tests they need."
Our complicated emotions about weight can have dangerous consequences. Fat isn't just a lump of pounds -- it's a biologically active substance that produces hormones like estrogen, which promotes tumor growth. "The more fat you have, especially around the abdomen, the more estrogen you'll produce," says Sharon Rosenbaum Smith, MD, medical director of the Comprehensive Breast Center at St. Luke's-Roosevelt Hospital Center in New York City. Exposure to high levels of the hormone may increase a woman's chances of getting breast cancer over time. In a recent Harvard study, women who gained 55 pounds or more after age 18 had about a one and a half times greater likelihood of developing the disease postmenopause than those who stayed at a healthy weight.
Fat may also play a role in producing chronic inflammation, which can lead to a number of diseases, including breast cancer. "Fat tissue has a direct connection to the immune system," explains Kristin Campbell, PhD, assistant professor of physical therapy at the University of British Columbia in Vancouver. "It appears to send out signals that trigger inflammation," which may cause tumors to form.
In addition, overweight women are more likely to suffer from metabolic syndrome, a combination of conditions -- including high blood pressure and high cholesterol -- that can raise a woman's risk for heart disease, stroke, diabetes and, according to a brand-new study, breast cancer. Researchers suspect that one of the culprits in this case is insulin. "When people are inactive or overweight, they store the glucose they get from food in fat rather than in muscle," Irwin notes. Higher amounts of body fat amp up the body's production of estrogen as well as a chemical called insulin-like growth factor, both of which cause breast cells to grow rapidly, increasing the odds that cancer will develop. "Even being thin may not help if you're a couch potato," Irwin says.
The good news is that lowering your breast cancer odds is as simple as taking a brisk 30-minute walk at least three times a week. "In a study, we found that women who get more than 60 minutes of aerobic exercise weekly significantly reduce their risk beginning after age 30," says lead researcher Lisa Sprod, PhD, research assistant professor of radiation oncology at the University of Rochester in New York. And it's never too late to start. "Even if you weren't active before that time, you can still get maximum cancer protection," Sprod says.
Exercise's knockout punch comes from keeping weight down and blasting fat. But it helps in other ways too. For one thing, active women tend to have lower estrogen levels. "It's possible that moderate workouts cause shifts in menstruation patterns over time -- lengthening the time between periods, for instance -- that may reduce a woman's exposure to estrogen during her lifetime," Campbell says. Researchers believe that working out can also reduce inflammation. And it definitely lowers insulin levels. "Insulin is very sensitive to lifestyle changes, making it a strong risk factor for breast cancer," Irwin says. In one recent study, doing 90 minutes of aerobic exercise a week, along with two sessions of resistance training, lowered insulin production by 28 percent. That's enough to boost survival rates for women with breast cancer almost as much as chemotherapy does. "If lowering insulin accomplishes that, it stands to reason that it would help prevent breast cancer from occurring in the first place," Irwin explains.
So bike, power walk, take a dance class; do whatever you enjoy. Just keep the activity up -- and your weight down. And while you're at it, eat a diet that includes plenty of fruits and vegetables containing cancer-fighting antioxidants. Among breast cancer survivors, that workout-good food combo appears to cut the risk of death within 10 years of diagnosis to half that of women who just exercise or who only eat a healthy diet, according to research. "There seems to be a cluster effect," says lead study author John P. Pierce, PhD, director of cancer prevention at the Moores University of California, San Diego Cancer Center in La Jolla. "Diet is most powerful in conjunction with physical activity and weight control."
All this research leads Tina Mitsis to believe that even with her ominous family history of breast cancer, she's getting things right. "Exercising and eating well make me feel I'm in control of my health," she says. "I really believe these are the smartest things any woman can do to protect herself."
If your BMI (body mass index) is 25 or above, work to lose 10 percent of your weight.
Exercise for two to three hours a week for the ultimate protection, says Melinda Irwin, PhD, associate professor of epidemiology and public health at Yale School of Medicine. "Aim for 60 percent of your maximum oxygen intake, where you have to take a deep breath every other word if you're talking," she adds.3. Schedule regular sweat sessions.
Chores don't have the same anticancer effect as working out, because "they tend to be start-and-stop," Irwin explains. "You could spend an hour in the garden and raise your heart rate for a total of just 15 minutes. When you exercise, you get continuous moderate-intensity activity."4. Veg out.
Eat cruciferous vegetables like broccoli, cauliflower, and kale. They contain isothiocyanates and indole-3-carbinol, compounds that may prevent the growth of tumors.
Originally published in FITNESS magazine, November/December 2009.