Physical Activity and Risk of Breast Cancer Among Postmenopausal Women

Abstract

Background Physical activity has many health benefits. Although greater activity has been related to lower postmenopausal breast cancer risk, important details remain unclear, including type, intensity, and timing of activity, and whether the association varies by subgroups. Methods Within the prospective Nurses’ Health Study, we assessed the associations of specific and total activity, queried every 2–4 years since 1986, with breast cancer risk. Cox proportional hazards models were used to calculate hazard ratios (HR) and 95% confidence intervals (CI). Results Over 20 years’ follow-up (1986–2006), 4,782 invasive breast cancer cases were documented among 95,396 postmenopausal women. Compared with <3 MET-hrs/wk (<1 hr/wk walking), women engaged in higher amounts of recent total physical activity were at lower breast cancer risk (for ≥27 MET-hrs/wk (~1 hr/day brisk walking) HR=0.85, 95% CI=(0.78–0.93), p-trend<0.001). Compared with women who were least active at menopause and through follow-up (<9 MET-hrs/wk, ~30 minutes of walking at an average pace on most days of the week), women who increased activity were at lower risk (<9 MET-hrs/wk at menopause, ≥9 MET-hrs/wk during follow-up HR=0.90, 95% CI=(0.82–0.98)). Among specific activities modeled simultaneously, brisk walking was associated with lower risk (HR=0.91, 95% CI=(0.84–0.98) per 20 MET-hrs/wk (5 hrs/wk)). The association with total activity did not differ significantly between estrogen and progesterone receptor-positive (ER+/PR+) and ER−/PR− tumors (p-heterogeneity=0.65). Conclusions Our findings suggest that moderate physical activity, including brisk walking, may reduce postmenopausal breast cancer risk and that increases in activity after menopause may be beneficial.

Recent Recreational Physical Activity and Breast Cancer Risk in Postmenopausal Women in the E3N Cohort

“…HRs for hormone receptor-defined invasive breast cancer according to level of recreational physical activity within the previous 4 years Contrary to most studies, which have not found that the relation between physical activity and breast cancer risk was modified by weight changes before inclusion (9,11,13,21,30), three articles report that the risk decrease associated with baseline physical activity is restricted to postmenopausal women with limited weight gain between youth and baseline (22,31,32). However, a weight gain before baseline may be associated with a decrease in physical activity after baseline (33).…”

“…However, the leanness of E3N women did not allow to explore the effect in higher categories of BMI or waist circumference. Similarly, most studies did not observe modifications in this relation according to hormone receptor status during postmenopause (6,10,13,(22)(23)(24)(25)(26). The risk reduction was limited to ER À (27) and PR þ (28) subtypes in two prospective studies and apparent only for postmenopausal ER þ /PR À (29) and ER þ /PR þ (25) cancers in two other studies (no tests for homogeneity).…”

“…However, in our study, the fact that the association with recreational physical activity did not vary significantly between ER/PR subtypes may also be due to a lack of statistical power, owing to the small number of cases in ER À subtypes. Only a few studies simultaneously considered recent and earlier physical activity, and their results conflict (6)(7)(8)(9)(10)(11)(12)(13). In line with our findings, in the Nurses' Health Study (13), women who were active close to menopause but not later did not have a lower risk of breast cancer than the least active women (<9 MET-h/week) during both periods, whereas women who were recently active had a risk 10% lower, regardless of whether or not they were active around menopause.…”

“…Their results were conflicting: two reported no association of breast cancer risk with either past or recent physical activity (7,9); one showed an association with recreational physical activity at the age of 12 to 22 years, but not after the age of 35 years (8); and two reported an association with physical activity at baseline, but not earlier (10,11). To our knowledge, only one prospective study (13) has investigated both past (at baseline, close to menopause) and recent (during the previous 2-4 years) physical activity in postmenopausal women. In that study, which had a 20-year follow-up period, only recent physical activity was inversely associated with breast cancer risk.…”

The impact of physical activity on cancer prevention and survivorship

“…A comparison of PA measurements in adults revealed that a dose response was seen in the reduction in the risk of developing cancer at higher levels of PA (600-3,999 METs minutes/week and 4,000-7,999 METs minutes/week vs. < 600 METs minutes/week), with risk reduction ranging from 3% to 14% for breast cancer and 10% to 21% for colorectal cancer [19]. Increased PA has also been described as beneficial for post-menopausal women diagnosed with breast cancer, and the timing of initiating exercise is also important [20]. The risk of gastric cancer was found to be 21% lower in persons with high levels of PA than in those with low levels of PA [21].…”