Table 2.

HRs and 95% CIs for the associations between physical activity and breast cancer risk, The Sister Study

		Overall		Premenopausal		Postmenopausal
	PY	N cases	HR^a^,^b (95% CI)	N cases	HR^a (95% CI)	N cases	HR^a (95% CI)
Total average hours/week
Continuous	421,807	3,017	0.99 (0.97–1.00)	533	1.03 (1.00–1.06)	2,460	0.98 (0.96–0.99)
0–<1	140,497	1,035	1.00	170	1.00	859	1.00
1–<4	173,872	1,220	0.91 (0.84–0.99)	225	1.13 (0.92–1.38)	983	0.87 (0.79–0.95)
4–<7	70,425	506	0.90 (0.81–1.01)	95	1.29 (1.00–1.66)	408	0.83 (0.74–0.94)
≥7	37,013	256	0.85 (0.74–0.98)	43	1.35 (0.96–1.89)	210	0.77 (0.66–0.90)
Total average MET-hours/week
Continuous (IQR increase)	421,807	3,017	0.97 (0.93–1.00)	533	1.08 (1.01–1.16)	2,460	0.92 (0.89–0.97)
Quartile 1	102,481	791	1.00	121	1.00	666	1.00
Quartile 2	110,532	753	0.86 (0.78–0.95)	131	0.99 (0.77–1.27)	616	0.83 (0.74–0.93)
Quartile 3	101,971	736	0.88 (0.79–0.97)	126	1.14 (0.88–1.47)	602	0.83 (0.74–0.92)
Quartile 4	106,822	737	0.83 (0.75–0.92)	155	1.25 (0.98–1.60)	576	0.75 (0.67–0.85)
At least one activity in the past 12 months
No	69,105	524	1.00	73	1.00	449	1.00
Yes	352,943	2,493	0.89 (0.81–0.98)	460	1.26 (0.98–1.62)	2,011	0.82 (0.74–0.91)

Abbreviations: PY, person-years.
↵^aAdjusted for race, residence type, education, parity, alcohol use, and smoking status.
↵^bBorderline violation of proportional hazards assumption.