Table 3.
Pooled hazard ratio (HR) (95% confidence interval (CI)) for the risk of all-cause mortality in relation to lifetime total breastfeeding duration, stratified by pre-pregnancy lifestyle factors and parity across the reproductive lifespan among 166,708 women from the NHS (1986-2016) and NHS II (1989-2019).a
| Stratified factors across the reproductive lifespan | Lifetime total breastfeeding duration |
|
|---|---|---|
| ≤3 months | >3 months | |
| AHEI diet quality score | ||
| Top 40% (n=13,821 deaths) | 1.00 [Reference] | 0.95 (0.92, 0.99) |
| Bottom 60% (n=22,813 deaths) | 1.00 [Reference] | 0.93 (0.91, 0.96) |
| P for multiplicative interactionb | 0.32 | |
| Smoking status | ||
| Never (n=14,074 deaths) | 1.00 [Reference] | 0.95 (0.91, 0.98) |
| Current/ever (n=22,560 deaths) | 1.00 [Reference] | 0.92 (0.90, 0.95) |
| P for multiplicative interactionb | 0.17 | |
| BMI | ||
| <25 kg/m2 (n=16,187 deaths) | 1.00 [Reference] | 0.97 (0.94, 1.00) |
| ≥25 kg/m2 (n=20,391 deaths) | 1.00 [Reference] | 0.92 (0.89, 0.94) |
| P for multiplicative interactionb | 0.18 | |
| Physical activity | ||
| ≥30 min/day (n=4387 deaths) | 1.00 [Reference] | 0.94 (0.88, 1.00) |
| <30 min/day (n=32,247 deaths) | 1.00 [Reference] | 0.93 (0.91, 0.95) |
| P for multiplicative interactionb | 0.99 | |
| Alcohol consumption | ||
| 5-15 g/day (n=6013 deaths) | 1.00 [Reference] | 0.94 (0.89, 0.99) |
| <5 or >15 g/day (n=30,621 deaths) | 1.00 [Reference] | 0.94 (0.92, 0.96) |
| P for multiplicative interactionb | 0.92 | |
| Parity | ||
| 1 (n=3395 deaths) | 1.00 [Reference] | 0.88 (0.81, 0.96) |
| ≥2 (n=33,239 deaths) | 1.00 [Reference] | 0.95 (0.93, 0.98) |
| P for multiplicative interactionb | 0.057 | |
Cox proportional hazards regression models were stratified jointly by participants’ own age in years at the start of follow-up and calendar years of the current questionnaire cycle, with adjustment for race/ethnicity (non-Hispanic White; yes or no), age at first birth (<20, 20–24, 25–29, ≥30 years), woman's own birth weight (<5.5, 5.5–6.9, 7.0–8.4, 8.5–9.9, ≥10 lbs), oral contraceptive use during puberty (yes or no), infertility history (yes or no), woman's parents worked as professionals, managers, or executives during infancy (yes or no), woman's parents owned home during infancy (yes or no), maternal history of cancer (yes or no), parental history of CVD before age 60 years (yes or no), and time-varying pre-pregnancy smoking status (never smoker, former smoker: 1–14, ≥15 cigarettes/d, and current smoker: 1–14, 15–24, ≥25 cigarettes/d), alcohol drinking (0, 0.1–4.9, 5.0–14.9, 15.0–19.9, 20.0–29.9, or ≥30 g/d), exercise at moderate-to-high intensity (0, 0.01–1.0, 1.1–3.4, 3.5–5.9, or ≥6.0 h/week), and alternate healthy eating index (five categories), and body mass index (<21, 21–24.9, 25–29.9, 30–31.9, or ≥32 kg/m2), excluding the stratified variables.
Multiplicative interaction was estimated using multiplicative interaction terms between dichotomous breastfeeding duration and these stratified variables based on the Wald test.