Breast cancer survivors are among the women who could most benefit from regular physical activity, yet few meet national exercise recommendations during the 10 years after being diagnosed, according to a study by researchers at Fred Hutchinson Cancer Research Center. Prior studies and available evidence show a strong association between physical activity and reduced mortality, extended survival and higher quality of life among breast cancer survivors. With 2.9 million breast cancer survivors living in the U.S. and another 80,000 added annually, there is considerable interest in the factors that promote health and well-being among these women.
The current study, published online ahead of print in the journal Cancer Epidemiology, Biomarkers and Prevention, followed an ethnically diverse group of 631 breast cancer survivors ages 18-64 from New Mexico, Los Angeles County and western Washington for 10 years. Recreational aerobic activity was ascertained for each woman via interviews and questionnaires the year before diagnosis and again two, five, and 10 years after enrollment into the study.
Prior to diagnosis, 34 percent of the women met U.S. physical activity guidelines. This percentage remained unchanged two years later. The percentage of women who complied with the activity guidelines increased to 39.5 percent at five years but then dropped to 21.4 percent at 10 years. Overall, researchers found that fewer than 8 percent of the survivors met U.S. physical activity guidelines at all of the study time points.
U.S. physical activity guidelines call for at least 150 minutes per week of moderate exercise or at least 75 minutes per week of vigorous activity. Researchers focused on 16 recreational physical activities: fast walking, jogging, running, hiking, aerobics, bicycling, swimming, tennis, golf, skiing, Nordic track, fast dancing, bowling, rowing, horseback riding and light calisthenics.
"The American Cancer Society recommends that cancer survivors exercise for at least 150 minutes per week. Most survivors may also benefit from strength training exercises at least two days per week," said Caitlin Mason, Ph.D., corresponding author and a postdoctoral research fellow in the Public Health Sciences Division at Fred Hutch. "For survivors who have not been previously active, we advise that they gradually work up to these recommendations," she said.
The researchers were surprised by the large drop in activity between five- and 10-year follow-up. After taking into account factors such as age and body size at diagnosis, the study found no other personal characteristics or aspects related to the type of breast cancer or its treatment were significantly associated with the drop in activity between the five- and 10-year reporting periods.
"It seems unlikely that this pattern reflects aging alone given the consistency and magnitude of the trend across all age groups," the authors wrote. "Whether this reflects a cohort effect or a unique aspect of the cancer survivorship experience is unclear."
All of the women were enrolled in the HEAL (Health, Eating, Activity and Lifestyle) Study, which investigates methods to improve breast cancer survival.
Senior author Anne McTiernan, Ph.D., a member of the Public Health Sciences Division at Fred Hutch, is principal investigator of the multi-site study.
The HEAL Study cohort represents one of the few breast cancer survivor groups that has repeated assessments of physical activity for as long as a decade after diagnosis. The authors acknowledge that levels of inactivity may be underestimated because the women included in the study tended to be a bit younger and were less likely to smoke, have advanced disease or have limits to doing physical activity compared to survivors who were not followed for 10 years. The predictors of physical activity in this population remain poorly understood, according to the authors.
"Our inability to identify many significant predictors of long-term physical activity participation suggests that the factors influencing physical activity behaviors in breast cancer survivors are complex and may differ from those in the general population," the authors wrote. "Additional consideration of psychosocial factors and issues related to pain management, fatigue, and specific treatment effects may help to better understand the unique issues faced by cancer survivors and their impact on physical activity participation."
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"Long-term physical activity trends in breast cancer survivors" Cancer Epidemiology, Biomarkers and Prevention, 2013.