Search:
Menopause Live - IMS Updates
InFocus

Date of release: 09 December, 2008

Physical activity and breast cancer risk in postmenopausal women


Several recent papers have reported a decreased risk of breast cancer with physical activity. Is there any strong evidence in favor of the positive effect of exercise?


The aim of the paper from Leiztmann and colleagues [1] was to examine the type of activity and breast cancer risk in a prospective cohort enrolled in the Breast Cancer Detection Demonstration Project (BCDDP) Follow-up Study in the US. In 1979, the National Cancer Institute established the BCDDP Follow-up Study of 64,182 women enrolled in the original BCDDP screening study. A total of 32,269 women were followed from 1987 to 1998; several questionnaires (Q) were completed during the follow-up but only one was about physical activity (Q2). The questionnaire encompassed an extensive list of examples of moderate and vigorous activities that covered household, occupational and recreational or sporting activities. A total weekly MET-hour score (total physical activity) was calculated by summing up the weekly expenditures from non-vigorous and vigorous activities. New incident breast cancer cases were identified through pathology reports, linkage to state cancer registries, the National Death Index and from self-report. A total of 1506 postmenopausal breast cancer cases were ascertained, of which 260 (17%) were classified as in situ cancers. 


The range of total physical activity varied about 2.5-fold between the means of extreme quintiles. Women reported spending an average of 1.2 h/day in vigorous activity and 5.9 h/day in non-vigorous activity. Women who were physically more active tended to be slightly leaner, to have never smoked, to have a lower level of education and to have greater parity than physically less active women. The risk of breast cancer was inversely associated with physical activity. The most active women had an age-adjusted relative risk (RR) of 0.81 (95% confidence interval (CI) 0.69-0.95; p = 0.03), as compared with the least active women. The relative risk was slightly attenuated and became statistically non-significant after additional adjustment for potential confounding variables (RR = 0.86; 95% CI 0.73-1.01; p = 0.15). However, when stratifying the relation of physical activity to postmenopausal breast cancer by body mass index (BMI) categories, among normal weight and lean women, the multivariate RRs comparing extreme categories of total and vigorous activity were significant: 0.76 (95% CI = 0.61-0.94; p = 0.03) and 0.68 (95% CI = 0.54-0.85; p = 0.002), respectively, but were not significant in overweight, obese women. The test for interaction between vigorous activity and BMI was statistically significant (p = 0.008). The effect of physical activity was independent of the estrogen-receptor (ER) status.

Comment

This study has some limitations: the self-reported activity, which might be misclassified, and a single questionnaire for physical activity. It is, however, an additional report of the interaction between activity and breast cancer risk. Despite opposite conclusions in the literature, the recent studies have mostly reported an inverse relationship between physical activity and breast cancer risk in postmenopausal women. Two reviews [2,3] have reported that more than two-thirds of the published studies found a decrease of 20-30% in the risk of breast cancer with exercise.
Several questions, however, remain: is the intensity of exercise, as suggested here, important? The Women’s Health Initiative (WHI) cohort study and the E3N cohort study have observed a reduction of the risk despite the importance of the activity [4,5]. In the WHI, from 74,171 postmenopausal women, there was a decrease in the risk of breast cancer for a minimum of 7 h/week of exercise (moderate or vigorous) (RR = 0.39; 95% CI = 0.63-0.99). In the E3N cohort (90,509 pre- and postmenopausal French women), there was a linear relationship between the level of exercise and the protective effect of exercise. Similarly, the European cohort, EPIC, reporting on 218,168 pre- and postmenopausal women from nine European countries, also observed a decrease in breast cancer risk with household and occupational activities also being protective [6]. Similarly, a recent case-control Polish study showed that the level of global activity was always important: the more the woman is active, the less she will be at risk for breast cancer [7].
Is the age of activity important? This was not specifically addressed in the analyzed paper. However, in an American population (WHI) [4]) as well as in an Asian one [8], there was probably a cumulative effect of activity throughout a woman’s lifetime and the effect of exercise was protective irrespective of the age of the woman. In addition, in the Nurses’ Health Study, it is suggested, for premenopausal breast cancer, that the role of exercise is cumulative and that regular exercise is necessary [9].
Does the effect of exercise act only or mainly in lean women, as reported herein? In 11 cohort and five case-control studies, that have looked at the association between exercise and breast cancer according to BMI, there was a more important benefit in lean women but, still, overweight women do benefit [2,3,5,6,10]. However, in the case of obesity, this factor seems to remain predominant [4].
Do the other risk factors for breast cancer modify the beneficial effect of exercise? The existence of familial risk, HRT or ER-negative tumors does not cancel the benefit from exercise [2-6]. 
In conclusion, despite the limitations of this paper, it confirms most of the available evidence on the beneficial effect of exercise, whatever its intensity (possibly with a threshold) and independent of whether the tumor is ER-positive or -negative, except in obese women. This highlights the importance of educating our postmenopausal patients about weight control, which is more effective with regular physical activity [11]. Since exercise is also beneficial for cardiovascular diseases and other cancer prevention, it might be the aim of public health policy to develop means to increase its availability for all age categories.

Comentario

Anne Gompel
Unité de Gynécologie Endocrinienne, Hôtel-Dieu de Paris, Université Paris Descartes, Paris, France

    References

  1. Leitzmann MF, Moore SC, Peters TM, et al. Prospective study of physical activity and risk of postmenopausal breast cancer. Breast Cancer Res 2008;10:R92. October 31 [Epub ahead of print].
    http://www.ncbi.nlm.nih.gov/pubmed/18976449

  2. Friedenreich CM, Orenstein MR. Physical activity and cancer prevention: etiologic evidence and biological mechanisms. J Nutr 2002;132(Suppl 1):3456-64S. Published November, 2002.
    http://www.ncbi.nlm.nih.gov/pubmed/12421870

  3. Monninkhof EM, Elias SG, Vlems FA, et al. Physical activity and breast cancer: a systematic review. Epidemiology 2007;18:137-57. Published January, 2007.
    http://www.ncbi.nlm.nih.gov/pubmed/17130685

  4. McTiernan A, Kooperberg C, White E, et al. Recreational physical activity and the risk of breast cancer in postmenopausal women: the Womens Health Initiative Cohort Study. JAMA 2003;290:1331-6. Published September 10, 2003.
    http://www.ncbi.nlm.nih.gov/pubmed/12966124

  5. Tehard B, Friedenreich CM, Oppert JM, Clavel-Chapelon F. Effect of physical activity on women at increased risk of breast cancer: results from the E3N cohort study. Cancer Epidemiol Biomarkers Prev 2006;15:57-64. Published January, 2006.
    http://www.ncbi.nlm.nih.gov/pubmed/16434587

  6. Lahmann PH, Friedenreich C, Schuit AJ, et al. Physical activity and breast cancer risk: the European Prospective Investigation into Cancer and Nutrition. Cancer Epidemiol Biomarkers Prev 2007;16:36-42. Published January, 2007.
    http://www.ncbi.nlm.nih.gov/pubmed/17179488

  7. Peplonska B, Lissowska J, Hartman TJ, et al. Adulthood lifetime physical activity and breast cancer. Epidemiology 2008;19:226-36. Published March, 2008.
    http://www.ncbi.nlm.nih.gov/pubmed/18277160

  8. Matthews CE, Shu XO, Jin F, et al. Lifetime physical activity and breast cancer risk in the Shanghai Breast Cancer Study. Br J Cancer 2001;84:994-1001. Published April 6, 2001.
    http://www.ncbi.nlm.nih.gov/pubmed/11286483

  9. Maruti SS, Willett WC, Feskanich D, Rosner B, Colditz GA. A prospective study of age-specific physical activity and premenopausal breast cancer. J Natl Cancer Inst 2008;100:728-37. Published May 21, 2008.
    http://www.ncbi.nlm.nih.gov/pubmed/18477801

  10. Friedenreich CM, Cust AE. Physical activity and breast cancer risk: impact of timing, type and dose of activity and population subgroup effects. Br J Sports Med 2008;42:636-47. Published August, 2008.
    http://www.ncbi.nlm.nih.gov/pubmed/18487249

  11. Irwin ML, Yasui Y, Ulrich CM, et al. Effect of exercise on total and intra-abdominal body fat in postmenopausal women: a randomized controlled trial. JAMA 2003;289:323-30. Published January 15, 2003.
    http://www.ncbi.nlm.nih.gov/pubmed/12525233