Physical Activity Benefits Breast Cancer Survivors, but Role in Reducing Breast Cancer Risk Is Less Clear


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With elimination of physical inactivity, life expectancy of the world’s population might be expected to increase by 0.68 years. These findings make inactivity similar to the established risk factors of smoking and obesity.

Breast cancer survivors who engage in moderate to high levels of physical activity have reduced mortality and improved quality of life, according to recent studies. In addition, exercise may play a role in lowering the risk of breast cancer.

“Physical activity can hasten recovery from the immediate effects of treatment, prevent long-term effects, and may reduce the risk of recurrence and increase survival,” according to the latest report on cancer treatment and survivorship statistics, published in CA: A Cancer Journal for Clinicians.1 “In observational studies among breast cancer patients, moderate physical activity has been associated with a reduced risk of death from all causes (24%-67%) and breast cancer (50%-53%),” the report noted.

The authors stated that intervention studies “have shown that exercise can improve fatigue, anxiety, depression, self-esteem, happiness, and quality of life in cancer patients.” They caution that exercise for survivors of cancer “should be individualized and tailored according to the disease site and stage and the survivor’s capabilities.”

‘Consistent Evidence’

A systematic review of 27 observational studies reporting associations between physical activity and cancer-specific outcomes or all-cause mortality found “consistent evidence” that physical activity is associated with reduced mortality from breast cancer, with weaker associations for reduced colon cancer–specific and all-cause mortality. “The strongest evidence for an association between physical activity and cancer outcomes comes from studies of breast cancer survivors,” reported researchers from the National Cancer Institute, Fred Hutchinson Cancer Research Center in Seattle, and the University of Alberta, Edmonton, and Alberta Health Services–Cancer Care, Calgary, in Canada.

“Nearly all of the breast cancer studies report that physical activity is associated with a reduction in breast cancer-specific mortality as well as all-cause mortality; this risk reduction was statistically significant in nearly half of these studies, and there is evidence for a dose-response effect of decreasing mortality risk with increasing activity in roughly half of the studies.” The researchers noted that the evidence relates to physical activity before or after breast cancer diagnosis.

The investigators added that the “next strongest evidence for an association between physical activity and disease outcomes for survivors of other cancer sites has been found for cancer-specific and all-cause mortality in colorectal cancer survivors.” The study was published in the Journal of the National Cancer Institute.2

Toll of Inactivity

The Lancet Physical Activity Series Working Group estimated that physical inactivity worldwide causes 10% of the burden of disease from breast cancer (range, 5.6%–14.1%) and colorectal cancer (range, 5.7%–13.8%).3

“For our analysis of burden of disease, we calculated population attributable fractions … associated with physical inactivity using conservative assumptions for each of the major noncommunicable diseases, by country, to estimate how much disease could be averted if physical inactivity were eliminated. We used life-table analysis to estimate gains in life expectancy of the population,” the working group explained. The estimated population attributable fractions, calculated with adjusted relative risks associated with physical activity for the United States are 12.4% (range, 5.8%–19.2%) for breast cancer and 12.0% (range, 6.7%–17.4%) for colon cancer.

“Worldwide, we estimated that physical inactivity causes 6% to 10% of the major non-communicable diseases of coronary heart disease, type 2 diabetes, and breast and colon cancers. Furthermore, this unhealthy behavior causes 9% of premature mortality, or more than 5.3 million of the 57 million deaths in 2008,” the authors wrote.

“With elimination of physical inactivity, life expectancy of the world’s population might be expected to increase by 0.68 years,” they continued. “These findings make inactivity similar to the established risk factors of smoking and obesity. The added years of life need to be interpreted correctly: they seem low because they represent gains in the whole population (including inactive and active people), rather than in inactive people who become active. Because all the gain accrues to people who move from inactive to active, the increase in life expectancy in the inactive group alone is greater. For perspective, other research done in the USA estimated that inactive people would gain 1.3 to 3.7 years from age 50 years by becoming active.”

Augmenting Weight Loss

The Nutrition and Exercise for Women randomized controlled trial tested the independent and combined effects of three different 12-month-long reduced-calorie weight loss and moderate to vigorous aerobic interventions on serum concentrations of estrogens, free testosterone, and other potential breast cancer biomarkers in overweight and obese postmenopausal women. Results from the 399 participants who completed physical examinations and provided blood samples at 12 months found that weight loss ≥ 5% was associated with significantly greater reductions in estradiol, free estradiol, and free testosterone and significantly increased sex hormone–binding globulin, the researchers reported in the Journal of Clinical Oncology.4 Exercise interventions alone, however, “had little effect on sex hormones or the other potential breast cancer biomarkers.”

The authors asserted that their findings taken together with those of other studies of dietary and exercise interventions among postmenopausal women “suggest that weight loss is the key factor linking alterations in diet or exercise to sex hormone changes.”

They also pointed out that the “lack of effect of exercise alone does not agree with epidemiologic studies in which physical activity is associated with decreased risk of breast cancer. Therefore, exercise could play a role in reducing risk of postmenopausal breast cancer through different biologic mechanisms than were examined in this study. Exercise may also play a role in reducing breast cancer risk by augmenting dietary weight loss and maintenance, which will be critical for long-term risk reduction.” ■

Disclosure: Senior author of the study published in the Journal of Clinical Oncology, Dr. Anne McTiernan, has served as consultant or advisor for Merck, Metagenics, Novartis, Proctor & Gamble, and ZymoGenetics, owns stock in Merck, has received honoraria from Novartis and Wyeth, and has received research funding from Wyeth. All other authors of the studies discussed in this article reported no potential conflicts of interest.

References

1. Siegel R, DeSantis C, Virgo K, et al: Cancer treatment and survivorship statistics. CA Cancer J Clin 62:220-241, 2012.

2. Ballard-Barbash R, Friedenreich CM, Courneya KS, et al: Physical activity, biomarkers, and disease outcomes in cancer survivors: A systematic review. J Nat Cancer Inst 104:815-840, 2012.

3. Lee I-M, Shiroma EJ, Lobelo F, et al: Effect of physical inactivity on major non-communicable diseases worldwide: An analysis of burden of disease and life expectancy. Lancet 380:219-229, 2012.

4. Campbell KL, Foster-Schubert KE, Alfano CM, et al: Reduced-calorie dietary weight loss, exercise, and sex hormones in postmenopausal women: Randomized controlled trial. J Clin Oncol 30:2314-2326, 2012.



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