AICR Conference

FigureWASHINGTON, DC—In a country whose citizens are becoming heavier and more sedentary, evidence continues to emerge that lack of physical activity is a risk factor for a number of cancers, including those of the breast, colon, and endometrium. But now, new statistics presented at the annual research conference of the American Institute for Cancer Research (AICR) estimate that up to 49,000 cases of breast cancer and 43,000 cases of colon cancer occurring each year in the United States are linked to being sedentary. The findings, which suggest that sitting itself is a cancer risk factor, were presented at an AICR news briefing here. New findings from the Alberta Physical Activity and Breast Cancer Prevention (ALPHA) trial show that the inflammation marker C-reactive protein – which raises cancer risk – can be reduced by moderate to vigorous physical activity in postmenopausal women, said Christine Friedenreich, PhD, Senior Research Scientist for Population Health Research at Alberta (Canada) Health Services-Cancer Care. “There is very convincing evidence that there is risk reduction with activity,” said Dr. Friedenreich, who is also an Adjunct Professor at the University of Calgary. She said that for breast cancer, the greatest risk decreases were found for recreational and household activity (about a 21% drop in risk), followed by walking or cycling (about an 18% drop in risk) and occupational activity (about a 13% decrease). For colon cancer, Dr. Friedenreich said occupational activity is associated with about a 22% reduction in cancer risk, while recreational activity is associated with about a 23% decrease in cancer risk. Biologic mechanisms for the benefits of physical activity in lowering cancer risk include decreases in body fat, sex hormones, prostaglandins, gastrointestinal transit time, inflammation, and oxidative stress, along with increases in insulin sensitivity, immune function, and pulmonary function. In addition, she noted, inflammation increases cytokines that foster cell proliferation and suppress cell death, and the benefits of physical activity are relatively constant across body mass index (BMI) categories and for both men and women. ‘Just Sitting’ “The majority of people's time is spent just sitting,” said Neville Owen, PhD, Head of the Behavioral Epidemiology Laboratory at the Baker IDI Heart and Diabetes Institute in Melbourne, Australia; a National Health and Medical Research Council of Australia Senior Principal Research Fellow; and Professor of Health Behavior at the University of Queensland. “Sitting time is emerging as a strong candidate for being a cancer risk factor in its own right. It seems highly likely that the longer you sit, the higher your risk….This phenomenon isn't dependent on body weight or how much exercise people do. If you're sitting for 10 to 11 hours a day, then it's a big exposure across a whole day and across weeks and months. The world in which we live is designed to make us sit, but we as biological creatures were not designed to sit.” ‘Breaks in Sedentary Time’ Hypothesis Dr. Owen said there is evidence to support the “breaks in sedentary time” hypothesis, which states that “breaking up sedentary time with frequent transitions from sitting to standing has beneficial associations on biomarkers independent of total sedentary time. “People who break up sedentary time have on average about two inches less waist circumference than those who just sit.” He said he has found that in terms of insulin resistance and inflammation, “even breaks as short as one minute can lower these biomarkers.” Dr. Owen and his collaborators are now conducting a randomized clinical trial investigating the link between biomarkers of cancer risk and regular desk breaks and other activities that promote standing. He told OT, “Standing desks used to be much more common.” Asked by OT if physical activity is as beneficial for cancer survivors as it is in primary cancer prevention, Dr. Owen said yes—“very definitely; absolutely.” He noted that research on colorectal cancer survivors has shown that those who watched many hours of television gained more weight and raised their risk of cancer recurrence. “Television viewing time, a sign of sedentary behavior, appears to increase subsequent risk of weight gain in cancer survivors,” he said. ‘Break Up Your Day’ “Moving more means lowering cancer risk,” said Alice Bender, MS, RD, AICR's Nutrition Communications Manager. “AICR is saying to America, “Break up your day; make time plus break time equals cancer prevention.” She said AICR recommends at least 30 minutes of physical activity every day, but noted that this half hour is “just one sliver of the day,” which is why the organization is calling for more activity breaks throughout the day. By thinking in terms of break time, said Ms. Bender, Americans can infuse their day “with short periods of activity that can protect against many cancers.” Children Lawrence A. Soler, President and CEO of Partnership for a Healthier America, said the increase in sedentary lifestyles could be devastating for American children in terms of long-term cancer risk: “Since 1980 obesity among children has increased dramatically. It has doubled among children ages two to five, tripled among children ages six to 11, and almost quadrupled among children 12 to 19.” He added, “Today, nearly one in every three American children are overweight or obese at an estimated cost of $14 billion annually.” He praised First Lady Michelle Obama for launching her campaign to reduce childhood obesity, Let's Move! (www.letsmove.gov). Mr. Soler said that to help get children moving and lower their risk of cancer and other diseases, “We have to do more. We have to work with mayors and schools and work with parents and caregivers and kid.…We have to be relentless in our efforts.” Agreeing with Dr. Owen and Ms. Bender, Mr. Soler said, “We have to have activity breaks as part of the everyday routine.” Related Research Related research presented at the AICR meeting supports the association of physical activity with reduced cancer risk. Some of the research showed that obesity and inactivity are increasing in parts of the world where people have traditionally been leaner and fitter. For example, a study of 1,059 Nigerian government office workers from the Harvard School of Public Health, the Institute of Human Virology at the University of Maryland, and the Institute of Human Virology in Nigeria showed that urbanized Nigerian adults have adopted a sedentary lifestyle. As a result, levels of obesity in this group are approaching those in the West.

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