7 hours/week of moderate-to-vigorous activity during the past 10 years was associated with 16% reduced risk of postmenopausal breast cancer (RR:0.84; 95%CI:0.76,0.93) compared with inactivity. The association remained statistically significant after adjustment for BMI (RR:0.87; 95%CI:0.78,0.96). Neither moderate-to-vigorous activity during other periods of life nor light intensity activity during any period of life was related to breast cancer risk, and associations did not vary by tumor characteristics. Conclusion A high level of recent, but not historical, physical activity of moderate-to-vigorous intensity is associated with reduced postmenopausal breast cancer risk. More precise recall of recent physical activity than activity in the distant past is one possible explanation for our findings."/>
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Table 5 Relative risk (RR) and 95% confidence intervals (CI) for the association of moderate-to-vigorous physical activity during four periods of life with breast cancer incidence: 118,899 postmenopausal women in the NIH-AARP Diet and Health Study

From: Intensity and timing of physical activity in relation to postmenopausal breast cancer risk: the prospective NIH-AARP Diet and Health Study

Moderate-to-vigorous activity No.
cancers*
n = 4287
RR 95%
CI
RR†† 95%
CI
RR§ 95%
CI
RR£ 95%
CI
Ages 15-18 years             
   Never/Rarely 541 1.00 (ref.)   1.00 (ref.)    1.00 (ref.)    1.00 (ref.)   
   <1 hour/week 394 1.11 0.98, 1.27 1.12 0.98 1.27 1.10 0.97 1.26 1.12 0.98 1.27
   1-3 hours/week 936 1.05 0.95, 1.17 1.05 0.94 1.17 1.04 0.93 1.16 1.05 0.94 1.16
   4-7 hours/week 950 1.02 0.92, 1.14 1.01 0.91 1.13 1.00 0.89 1.12 1.01 0.91 1.13
   >7 hours/week 1415 1.02 0.92, 1.12 1.03 0.93 1.14 1.02 0.91 1.14 1.02 0.93 1.13
Ages 19-29 years             
   Never/Rarely 415 1.00 (ref.)   1.00 (ref.)    1.00 (ref.)    1.00 (ref.)   
   <1 hour/week 384 1.09 0.95, 1.25 1.08 0.94 1.24 1.07 0.93 1.23 1.08 0.94 1.24
   1-3 hours/week 976 1.07 0.95, 1.20 1.06 0.94 1.19 1.05 0.93 1.18 1.06 0.94 1.19
   4-7 hours/week 1080 1.00 0.89, 1.12 1.01 0.90 1.13 1.01 0.89 1.13 1.01 0.90 1.13
   >7 hours/week 1375 0.97 0.87, 1.08 1.01 0.90 1.13 1.02 0.90 1.15 1.01 0.90 1.13
Ages 35-39 years             
   Never/Rarely 392 1.00 (ref.)   1.00 (ref.)    1.00 (ref.)    1.00 (ref.)   
   <1 hour/week 421 1.12 0.98, 1.28 1.11 0.97 1.27 1.09 0.95 1.25 1.11 0.97 1.27
   1-3 hours/week 963 1.00 0.89, 1.13 0.99 0.88 1.11 0.98 0.87 1.11 0.99 0.88 1.12
   4-7 hours/week 1174 1.03 0.92, 1.16 1.03 0.92 1.15 1.04 0.92 1.18 1.04 0.93 1.16
   >7 hours/week 1288 0.94 0.84, 1.06 0.97 0.87 1.09 0.99 0.87 1.12 0.98 0.88 1.10
Past 10 years             
   Never/Rarely 646 1.00 (ref.)   1.00 (ref.)    1.00 (ref.)    1.00 (ref.)   
   <1 hour/week 507 1.06 0.94, 1.19 1.05 0.94 1.18 1.03 0.92 1.16 1.06 0.94 1.19
   1-3 hours/week 1071 0.93 0.84, 1.02 0.91 0.83 1.00 0.90 0.81 1.00 0.93 0.84 1.02
   4-7 hours/week 1106 0.94 0.86, 1.04 0.92 0.83 1.01 0.91 0.82 1.01 0.94 0.85 1.04
   >7 hours/week 928 0.84 0.76, 0.93 0.84 0.76 0.93 0.85 0.76 0.95 0.87 0.78 0.96
  1. Number of cancer cases may not add up to total (n = 4287) due to missing physical activity values
  2. † Relative risks adjusted for age (continuous)
  3. †† Relative risks adjusted for: age (continuous); race/ethnicity (white, black, Hispanic, Asian/Pacific Islander/American Indian); education level (<12 years or high school equivalent, 12 years or high school equivalent, post-high school vocational or technical training, some college, college graduate, post-graduate); smoking status (non-smoker, former, current); alcohol intake (grams/day, quintiles adjusted for total energy intake); family history of breast cancer (no, yes); age at menarche (<13, 13-14, ≥ 15 years); age at first birth (nulliparous, <20, 20-24, 25-29, 30+ years); parity (number of children: 0, 1-2, 3 or more); age at menopause (<40, 40-44, 45-49, 50-54, ≥ 55 years); menopausal hormone use (never, ever)
  4. §Relative risks additionally adjusted for frequency of other type of physical activity (either light or moderate-to-vigorous) during that same time period
  5. £ Relative risks additionally adjusted for body mass index (BMI: <25.0, 25.0-29.9, 30.0-34.9, ≥ 35.0 kg/m2)