February 27, 2017 | by Samantha Bonar
But so much about cancer is out of our control. Your unique genetic makeup, the environment, your gender and race all factor into whether or not you may, at some point, develop cancer.
The race to reduce your cancer risk is a marathon, not a sprint. And while it is impossible to prevent cancer, there are strategies that, when implemented consistently over your lifetime, may lower your risk of cancer.
“There’s a reason that these are the same factors that a lot of other studies are looking at. They are the things that are more and more associated with cancer,” said Lacey, one of the California Teachers Study's principal investigators.
“Physical activity has been one of the main focuses of the study from the very beginning,” said Lacey. “For breast cancer, the data are quite good that physical activity reduces the risk of developing both in situ cancer and invasive breast cancer. The women who have had higher levels of long-term and strenuous physical activity are less likely to develop breast cancer than women who are less active.
“It’s one of the most exciting areas of research right now,” Lacey added. It appears that physical activity lowers levels of estrogen, he said, which is something that “we know is like gasoline to the development of breast cancer.”
Another hypothesis, he said, is that physical activity can affect the immune system in positive ways, such as by reducing inflammation that might lead to breast cancer. The same types of strenuous physical activity were associated with reduced risk of endometrial cancer, he said. “Endometrial cancer is really driven by estrogen, even more so than breast cancer,” he said.
The level of activity that appears to make a difference is at least 3.5 hours a week of such activities as running, aerobics, dancing or swimming. Women who participated in exercise had “notably lower risk” of breast cancer compared to those who exercised less than half an hour per week.
“It doesn’t require marathon training,” Lacey said.
In terms of the second major risk factor, “Physical activity and obesity are directly related,” Lacey said. “Obesity is a risk factor for breast cancer as well, particularly breast cancer that occurs after menopause. Those two things — physical activity and obesity — have traveled together. But it looks as though even when we try to control for one, the other is still a risk factor independently.
“The obesity component of that might tie into inflammation. It looks like adipose tissue can also affect the immune system. Precisely how that affects breast cancer is something that a whole number of folks are studying,” Lacey said.
Obesity is an even stronger risk factor for endometrial cancer, Lacey said. It is also thought to increase the risk of colorectal cancer. “That makes sense, because for those three tumors among women — breast cancer, endometrial cancer, colon cancer — there’s a strong estrogen component,” he said. “Precisely how estrogen and physical activity and obesity interact is something that’s being actively studied.”
A third major cancer risk factor for women gleaned from the study is smoking. “We see a couple things. With such a small number of smokers in California compared to other states, we do see that passive smoking is an important source of smoke for cancer risk,” Lacey said. The study has found that women exposed to passive smoke — secondhand smoke, environmental smoke — are at a higher risk for breast cancer.
Another analysis of the study data saw about a 50 percent increased risk of developing non-Hodgkin’s lymphoma among women exposed to passive smoke.
“You don’t have to be the one holding the cigarette or smoking the tobacco to be subject to the risk that comes with being around smoke,” Lacey said.
Based on these key takeaways from the study, Lacey offers some general recommendations that “reinforce a lot of what we’ve heard for years”:
“Over 50 percent of cancers are caused we think by lifestyle factors: physical activity, smoking, sun exposure, obesity,” he said. “Certainly with the decline in levels of smoking but the rise in levels of obesity, we can go back to those same things: a general healthy lifestyle. Some physical activity — as little as a half-hour a day. It doesn’t require massive changes in lifestyle: not smoking, protection from the sun, daily exercise.”
Another “crystal clear” component in cancer prevention is the importance of screening and early detection, he said. That includes colonoscopies, mammography, Pap smears and HPV (human papillomavirus) testing and vaccination. “A combination of prevention, screening and healthy lifestyle — if those three things were in place we could see some real significant progress in reduction in the burden of cancer across the population,” he said.
Stories of Hope is a monthly series that explores important issues in health care. During National Cancer Prevention Month, we're taking a closer look at the science — and the psychology — behind cancer prevention.
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