Table 4.

Relative risk (95% confidence interval) of invasive breast cancer among premenopausal women according to acetaminophen use in the Nurses' Health Study II, 1989−2003

	Cases	Simple	MV
Regular use (≥2 times/week)
Non-users	706	1.00 (ref)	1.00 (ref)
Past users	375	1.00 (0.87−1.16)	1.03 (0.89−1.19)
Current users	185	0.96 (0.82−1.13)	0.99 (0.84−1.16)
<5 yrs	142	0.94 (0.78−1.13)	0.97 (0.81−1.16)
≥5 yrs	43	1.05 (0.76−1.43)	1.07 (0.78−1.47)
p-trend		0.93	0.91
Frequency of use (follow-up 1995−2003)
Non-users	325	1.00 (ref)	1.00 (ref)
Past users	253	0.94 (0.79−1.12)	0.96 (0.81−1.14)
Current users
1 days/wk	152	0.91 (0.75−1.11)	0.93 (0.76−1.13)
2−3 days/wk	68	0.90 (0.69−1.17)	0.94 (0.72−1.22)
4−5 days/wk	18	0.94 (0.58−1.51)	1.00 (0.62−1.61)
6+ days/wk	16	1.02 (0.61−1.69)	1.06 (0.64−1.76)
p-trend		0.68	0.60
Regular use (≥2 times/week)
ER+/PR+ Non-users	362	1.00 (ref)	1.00 (ref)
Past users	224	0.97 (0.81−1.17)	1.00 (0.83−1.20)
Current users	97	0.95 (0.76−1.19)	0.98 (0.78−1.22)
ER-/PR- Non-users	121	1.00 (ref)	1.00 (ref)
Past users	59	1.01 (0.71−1.43)	1.00 (0.70−1.43)
Current users	33	1.03 (0.70−1.51)	1.00 (0.67−1.47)

*Multivariate model adjusted for factors listed in Table 2 footnote