TABLE 3.

Association between asthma and incident breast cancer among 202,055 participants in the Nurses' Health Studies I and II from 1976 until 2016, and 1989 until 2015, respectively.

	NHS						NHS II						Meta‐analysis
	Person‐years	No. of cases	Age‐adjusted HR		Multivariable‐adjusted HR		Person‐years	No. of cases	Age‐adjusted HR		Multivariable‐adjusted HR		Multivariable‐adjusted HR
			HR	95% CI	HR	95% CI			HR	95% CI	HR	95% CI	HR	95% CI
Asthma a
No (ref.)	1,943,820	6669	1	—	1	—	1,954,592	3188	1	—	1	—	1	—
Yes b	260,980	829	0.96	0.89–1.03	0.92	0.86–0.99	234,368	410	0.96	0.87–1.07	0.93	0.84–1.03	0.92	0.87–0.98
Non‐atopic asthma	27,004	87	0.92	0.75–1.14	0.91	0.73–1.12	18,012	34	1.00	0.71–1.40	1.00	0.71–1.41	0.93	0.78–1.12
Atopic asthma	133,905	444	0.99	0.90–1.09	0.95	0.86–1.04	208,765	363	0.96	0.86–1.07	0.92	0.82–1.02	0.93	0.87–1.01

Note: Multivariable models were adjusted for age, race, smoking status, family history of breast cancer in first‐degree relative(s), history of benign breast disease, height, body mass index at age 18, current BMI, age at menarche, parity, age at first birth, menopausal status, use of postmenopausal hormones, moderate and vigorous physical activity, and alcohol consumption. Values with statistical significance at the 0.05‐level are highlighted in bold.

Abbreviations: CI, confidence interval; HR, hazard ratio; NHS, nurses' health study.

^a Modeled as an updated exposure during follow‐up.

^b Observations with missing values for height were excluded from analyses. Observations with missing values for other variables were included in the model as a “missing” category.