Duration of lactation and incidence of maternal hypertension: a longitudinal cohort study

Abstract

Never or curtailed lactation has been associated with an increased risk for incident hypertension, but the effect of exclusive breastfeeding is unknown. The authors conducted an observational cohort study of 55,636 parous women in the US Nurses' Health Study II. From 1991 to 2005, participants reported 8,861 cases of incident hypertension during 660,880 person-years of follow-up. Never or curtailed lactation was associated with an increased risk of incident hypertension. Compared with women who breastfed their first child for ≥12 months, women who did not breastfeed were more likely to develop hypertension (hazard ratio (HR) = 1.27, 95% confidence interval (CI): 1.18, 1.36), adjusting for family history and lifestyle covariates. Women who never breastfed were more likely to develop hypertension than women who exclusively breastfed their first child for ≥6 months (HR = 1.29, 95% CI: 1.20, 1.40). The authors found similar results for women who had never breastfed compared with those who had breastfed each child for an average of ≥12 months (HR = 1.22, 95% CI: 1.13, 1.32). In conclusion, never or curtailed lactation was associated with an increased risk of incident maternal hypertension, compared with the recommended ≥6 months of exclusive or ≥12 months of total lactation per child, in a large cohort of parous women.

Figure 1.

Study population, Nurses’ Health Study II, United States, 1991–2005. Participants were excluded from follow-up if they were diagnosed with hypertension or died. Participants were skipped in the current follow-up cycle if they were nulliparous, had unknown hypertension status, or were missing information on current body mass index. BMI, body mass index; CVD, cardiovascular disease; HTN, hypertension.

Figure 2.

Association between duration of total breastfeeding for the first child and incident hypertension among 55,636 parous women in the Nurses’ Health Study II, United States, 1991–2005. Adjusted for age and inverse probability weight, derived from a multinomial logistic regression model for probability of each breastfeeding duration category as a function of maternal body mass index at age 18 years (linear and quadratic), year of first birth (linear and quadratic), self-reported history of preeclampsia, gestational hypertension, gestational diabetes, birth of an infant at <37 weeks’ gestation, birth of an infant weighing <2,500 g, miscarriage or stillbirth at >12 weeks’ gestation, smoking status, vigorous physical activity, alcohol consumption, Dietary Approaches to Stop Hypertension (DASH) diet score quintile, family history of hypertension, current oral contraceptive use, current nonnarcotic analgesic use, and self-reported race.