Table 3.

Incident myocardial infarction and duration of lactation, stratified by time since last birth among parous women in the Nurses’ Health Study: Prospective analysis using cases from 1986 to 2002; all models adjusted for age, parity, and history of stillbirth.

Cumulative duration of lactation (months)	None	> 0–3	> 3–6	> 6–11	> 11–23	>23	P for trend
No birth in last 30 years
No of cases	616	426	186	130	133	54
Person-years	211,951	146,625	67,250	49,338	54,082	21,443
Age, parity and stillbirth-adjusted HR (95% CI)	1.0 (ref)	0.96 (0.85 – 1.09)	0.94 (0.79 – 1.11)	0.91 (0.75 – 1.1)	0.82 (0.68 – 0.99)	0.77 (0.58 – 1.02)	0.01
Multivariate-adjusted HR (95% CI)*	1.0 (ref)	1.04 (0.92 – 1.18)	1.02 (0.86 – 1.21)	1.02 (0.84 – 1.24)	0.95 (0.78 – 1.15)	0.90 (0.67 – 1.19)	0.33
Birth in last 30 years
No of cases	421	201	118	94	108	53
Person-years	282,716	160,044	94,336	83,155	110,663	69,362
Age, parity and stillbirth-adjusted HR (95% CI)	1.0 (ref)	0.81 (0.69 – 0.96)	0.87 (0.71 – 1.07)	0.81 (0.65 – 1.02)	0.71 (0.57 – 0.88)	0.50 (0.37 – 0.67)	<0.001
Multivariate-adjusted HR (95% CI)*	1.0 (ref)	0.94 (0.79 – 1.12)	0.98 (0.8 – 1.21)	0.96 (0.76 – 1.21)	0.89 (0.71 – 1.1)	0.66 (0.49 – 0.89)	0.02

^*Hazard ratio (HR) and 95% CI adjusted for age, parity, history of stillbirth, BMI at age 18, birth weight of subject, parental history of myocardial infarction before age 60, diet quintile, physical activity, smoking, menopausal status, and use of aspirin, alcohol, multivitamins, and postmenopausal hormones.