Laurie A. Nommsen-Rivers

Differences in morbidity between breast-fed and formula-fed infants

To determine whether breast-feeding is protective against infection in relatively affluent populations, morbidity data were collected by weekly monitoring during the first 2 years of life from matched cohorts of infants who were either breast fed (BF) (N = 46) or formula fed (FF) (N = 41) until at least 12 months of age. Cohorts were matched for characteristics such as birth weight and parental socioeconomic status, and we controlled for use of day care in data analysis. Mean maternal educational level was high (16 years) in both groups. In the first year of life the incidence of diarrheal illness among BF infants was half that of FF infants; the percentage with any otitis media was 19% lower and with prolonged episodes (> 10 days) was 80% lower in BF compared with FF infants. There were no significant differences in rates of respiratory illness; nearly all cases were mild upper respiratory infections. Morbidity rates did not differ significantly between groups in the second year of life, but the mean duration of episodes of otitis media was longer in FF than BF infants (8.8 +/- 5.3 vs 5.9 +/- 3.5 days, respectively; p = 0.01). These results indicate that the reduction in morbidity associated with breast-feeding is of sufficient magnitude to be of public health significance.

A Randomized Study of the Effects of Aerobic Exercise by Lactating Women on Breast-Milk Volume and Composition

BACKGROUND The potential risks and benefits of regular exercise during lactation have not been adequately evaluated. We investigated whether regular aerobic exercise had any effects on the volume or composition of breast milk. METHODS Six to eight weeks post partum, 33 sedentary women whose infants were being exclusively breast-fed were randomly assigned to an exercise group (18 women) or a control group (15 women). The exercise program consisted of supervised aerobic exercise (at a level of 60 to 70 percent of the heart-rate reserve) for 45 minutes per day, 5 days per week, for 12 weeks. Energy expenditure, dietary intake, body composition, and the volume and composition of breast milk were assessed at 6 to 8, 12 to 14, and 18 to 20 weeks post partum. Maximal oxygen uptake and the plasma prolactin response to nursing were assessed at 6 to 8 and 18 to 20 weeks. RESULTS The women in the exercise group expended about 400 kcal per day during the exercise sessions but compensated for this energy expenditure with a higher energy intake than that recorded by the control women (mean [+/- SD], intake, 2497 +/- 436 vs. 2168 +/- 328 kcal per day at 18 to 20 weeks; P < 0.05). Maximal oxygen uptake increased by 25 percent in the exercising women but by only 5 percent in the control women (P < 0.001). There were no significant differences between the two groups in maternal body weight or fat loss, the volume or composition of the breast milk, the infant weight gain, or maternal prolactin levels during the 12-week study. CONCLUSIONS In this study, aerobic exercise performed four or five times per week beginning six to eight weeks post partum had no adverse effect on lactation and significantly improved the cardiovascular fitness of the mothers.

In-hospital formula use increases early breastfeeding cessation among first-time mothers intending to exclusively breastfeed.

OBJECTIVE To evaluate in-hospital formula supplementation among first-time mothers who intended to exclusively breastfeed and determined if in-hospital formula supplementation shortens breastfeeding duration after adjusting for breastfeeding intention. STUDY DESIGN We assessed strength of breastfeeding intentions prenatally in a diverse cohort of expectant primiparae and followed infant feeding practices through day 60. Among mothers planning to exclusively breastfeed their healthy term infants for ≥1 week, we determined predictors, reasons, and characteristics of in-hospital formula supplementation, and calculated the intention-adjusted relative risk (ARR) of not fully breastfeeding days 30-60 and breastfeeding cessation by day 60 with in-hospital formula supplementation (n = 393). RESULTS Two hundred ten (53%) infants were exclusively breastfed during the maternity stay and 183 (47%) received in-hospital formula supplementation. The most prevalent reasons mothers cited for in-hospital formula supplementation were: perceived insufficient milk supply (18%), signs of inadequate intake (16%), and poor latch or breastfeeding (14%). Prevalence of not fully breastfeeding days 30-60 was 67.8% vs. 36.7%, ARR 1.8 (95% CI, 1.4-2.3), in-hospital formula supplementation vs exclusively breastfed groups, respectively, and breastfeeding cessation by day 60 was 32.8% vs. 10.5%, ARR 2.7 (95% CI, 1.7-4.5). Odds of both adverse outcomes increased with more in-hospital formula supplementation feeds (not fully breastfeeding days 30-60, P = .003 and breastfeeding cessation, P = .011). CONCLUSIONS Among women intending to exclusively breastfeed, in-hospital formula supplementation was associated with a nearly 2-fold greater risk of not fully breastfeeding days 30-60 and a nearly 3-fold risk of breastfeeding cessation by day 60, even after adjusting for strength of breastfeeding intentions. Strategies should be sought to avoid unnecessary in-hospital formula supplementation and to support breastfeeding when in-hospital formula supplementation is unavoidable.

Comfort with the idea of formula feeding helps explain ethnic disparity in breastfeeding intentions among expectant first-time mothers.

OBJECTIVES Little is known regarding modifiable factors that may explain sociodemographic disparities in breastfeeding rates among women in the United States. Using a mediation model approach, we examined the relative contributions of breastfeeding and formula feeding psychosocial factors in explaining disparities in breastfeeding intentions. METHODS We interviewed 532 expectant first-time mothers regarding exposure to breastfeeding by others (breastfeeding exposure), comfort with ideas of breastfeeding (breastfeeding comfort) and formula feeding (formula feeding comfort), and breastfeeding self-efficacy. We used logistic regression to evaluate the independent and mediating effects of these variables on strength of intention to fully breastfeed for 6 months (breastfeeding intention). RESULTS The ethnic distribution of the sample was 41% white, non-Hispanic; 27% Hispanic; 14% African-American; 12% Asian; and 6% mixed or other ethnicity. In the overall sample, formula feeding comfort, breastfeeding comfort, and breastfeeding self-efficacy all independently predicted breastfeeding intention (p < 0.0001), but formula feeding comfort had the largest effect: adjusted odds of stronger breastfeeding intention increased threefold for each 1-level decrease (among four levels) in formula feeding comfort. The unadjusted odds (95% confidence interval) of stronger breastfeeding intention were 0.37 (0.24-0.58) for African-American versus non-African-American women; African-American women had higher formula feeding comfort (2.08 [1.32-3.29]) but similar breastfeeding comfort, breastfeeding self-efficacy, and breastfeeding exposure. Formula feeding comfort mediated 37% of the disparity in breastfeeding intentions between African-American and non-African-American women. CONCLUSIONS Formula feeding comfort strongly predicted and substantially mediated ethnic disparity in breastfeeding intention. These results suggest that research and public health efforts aimed at increasing exclusive breastfeeding rates should include consideration of formula feeding attitudes.

Risk factors for suboptimal infant breastfeeding behavior, delayed onset of lactation, and excess neonatal weight loss

Even mothers who strongly want to breast feed their infants could have difficulty getting started. This prospective community-based study was an attempt to identify risk factors other than sociocultural barriers that arerelated to poor lactation outcomes. Risk factors were sought for suboptimal infant breastfeeding behavior (SIBB), delayed lactation, and excessive neonatal weight loss. Participants gave birth to a healthy single infant at term and were willing to try breast feeding exclusively for at least 30 days. Trained lactation consultants provided guidance in such areas as correct positioning, demand feeding, and avoidance of supplements, and also evaluated infant breastfeeding behavior using the Infant Breast-feeding Assessment Tool. Weight loss exceeding 10% of birth weight on day 3 was considered excessive. The mean maternal age was 30.6 years and 56% of mothers were primiparous. Nearly 80% of subjects were non-Hispanic whites. The average educational level was high. These mothers expressed strongly positive attitudes toward breast feeding. SIBB was found in 49% of infants at baseline, 22% on day 3 and 14% on day 7. It correlated significantly with primiparity on days 0 and 3, with cesarean section (day 0 in multiparas), and with flat or inverted nipples. Other significant correlates of SIBB included using nonbreast milk fluids in the first 2 days of life, use of a pacifier, stage II labor lasting longer than 1 hour, and a maternal body mass index (BMI) greater than 27 kg/m 2 . Lactation was delayed in 22% of women, more frequently in primiparas, after cesarean section, and women having a prolonged second stage of labor, a high material BMI, flat or inverted nipples, or (in primiparas) a birth weight greater than 3600 g. Excessive weight loss was observed in 12% of neonates. It correlated with primiparity, a long labor, the use of labor medication (by multiparas), and infant status at birth. Excessive weight loss was 7.1-fold more likely if lactation was delayed and 2.6-fold more likely if SIBB was present on the first day of life.

RNA Sequencing of the Human Milk Fat Layer Transcriptome Reveals Distinct Gene Expression Profiles at Three Stages of Lactation

Aware of the important benefits of human milk, most U.S. women initiate breastfeeding but difficulties with milk supply lead some to quit earlier than intended. Yet, the contribution of maternal physiology to lactation difficulties remains poorly understood. Human milk fat globules, by enveloping cell contents during their secretion into milk, are a rich source of mammary cell RNA. Here, we pair this non-invasive mRNA source with RNA-sequencing to probe the milk fat layer transcriptome during three stages of lactation: colostral, transitional, and mature milk production. The resulting transcriptomes paint an exquisite portrait of human lactation. The resulting transcriptional profiles cluster not by postpartum day, but by milk Na:K ratio, indicating that women sampled during similar postpartum time frames could be at markedly different stages of gene expression. Each stage of lactation is characterized by a dynamic range (105-fold) in transcript abundances not previously observed with microarray technology. We discovered that transcripts for isoferritins and cathepsins are strikingly abundant during colostrum production, highlighting the potential importance of these proteins for neonatal health. Two transcripts, encoding β-casein (CSN2) and α-lactalbumin (LALBA), make up 45% of the total pool of mRNA in mature lactation. Genes significantly expressed across all stages of lactation are associated with making, modifying, transporting, and packaging milk proteins. Stage-specific transcripts are associated with immune defense during the colostral stage, up-regulation of the machinery needed for milk protein synthesis during the transitional stage, and the production of lipids during mature lactation. We observed strong modulation of key genes involved in lactose synthesis and insulin signaling. In particular, protein tyrosine phosphatase, receptor type, F (PTPRF) may serve as a biomarker linking insulin resistance with insufficient milk supply. This study provides the methodology and reference data set to enable future targeted research on the physiological contributors of sub-optimal lactation in humans.

Lactation and Neonatal Nutrition: Defining and Refining the Critical Questions

This paper resulted from a conference entitled “Lactation and Milk: Defining and refining the critical questions” held at the University of Colorado School of Medicine from January 18–20, 2012. The mission of the conference was to identify unresolved questions and set future goals for research into human milk composition, mammary development and lactation. We first outline the unanswered questions regarding the composition of human milk (Section I) and the mechanisms by which milk components affect neonatal development, growth and health and recommend models for future research. Emerging questions about how milk components affect cognitive development and behavioral phenotype of the offspring are presented in Section II. In Section III we outline the important unanswered questions about regulation of mammary gland development, the heritability of defects, the effects of maternal nutrition, disease, metabolic status, and therapeutic drugs upon the subsequent lactation. Questions surrounding breastfeeding practice are also highlighted. In Section IV we describe the specific nutritional challenges faced by three different populations, namely preterm infants, infants born to obese mothers who may or may not have gestational diabetes, and infants born to undernourished mothers. The recognition that multidisciplinary training is critical to advancing the field led us to formulate specific training recommendations in Section V. Our recommendations for research emphasis are summarized in Section VI. In sum, we present a roadmap for multidisciplinary research into all aspects of human lactation, milk and its role in infant nutrition for the next decade and beyond.

Excess Weight Loss in First-Born Breastfed Newborns Relates to Maternal Intrapartum Fluid Balance

OBJECTIVES: The objectives were to describe weight loss in a multiethnic population of first-born, predominantly breastfed, term infants and to identify potentially modifiable risk factors for excess weight loss (EWL). METHODS: Data on prenatal breastfeeding intentions, demographic characteristics, labor and delivery interventions and outcomes, breastfeeding behaviors, formula and pacifier use, onset of lactogenesis, and nipple type and pain were collected prospectively. Logistic regression analyses identified independent predictors of EWL (≥10% of birth weight) by using a preplanned theoretical model. RESULTS: EWL occurred for 18% of infants who received no or minimal (≤60 mL total since birth) formula (n = 229), including 19% of exclusively breastfed infants (n = 134) and 16% of infants who received minimal formula (n = 95). In bivariate analyses, EWL was associated (P < .05) with higher maternal age, education, and income levels, hourly intrapartum fluid balance, postpartum edema, delayed lactogenesis (>72 hours), fewer infant stools, and infant birth weight. In multivariate logistic regression analysis, only 2 variables predicted EWL significantly, namely, intrapartum fluid balance (adjusted relative risk for EWL of 3.18 [95% confidence interval [CI]: 1.35–13.29] and 2.80 [95% CI: 1.17–11.68] with net intrapartum fluid balance of >200 and 100–200 mL/hour, respectively, compared with <100 mL/hour) and delayed lactogenesis (adjusted relative risk: 3.35 [95% CI: 1.74–8.10]). CONCLUSIONS: EWL was more common in this population than reported previously and was independently related to intrapartum fluid balance. This suggests that intrapartum fluid administration can cause fetal volume expansion and greater fluid loss after birth, although other mechanisms are possible.

Breastfeeding Concerns at 3 and 7 Days Postpartum and Feeding Status at 2 Months

OBJECTIVE: We characterized breastfeeding concerns from open-text maternal responses and determined their association with stopping breastfeeding by 60 days (stopping breastfeeding) and feeding any formula between 30 and 60 days (formula use). METHODS: We assessed breastfeeding support, intentions, and concerns in 532 expectant primiparas and conducted follow-up interviews at 0, 3, 7, 14, 30, and 60 days postpartum. We calculated adjusted relative risk (ARR) and adjusted population attributable risk (PAR) for feeding outcomes by concern category and day, adjusted for feeding intentions and education. RESULTS: In 2946 interviews, 4179 breastfeeding concerns were reported, comprising 49 subcategories and 9 main categories. Ninety-two percent of participants reported ≥1 concern at day 3, with the most predominant being difficulty with infant feeding at breast (52%), breastfeeding pain (44%), and milk quantity (40%). Concerns at any postpartum interview were significantly associated with increased risk of stopping breastfeeding and formula use, with peak ARR at day 3 (eg, stopping breastfeeding ARR [95% confidence interval] = 9.2 [3.0–infinity]). The concerns yielding the largest adjusted PAR for stopping breastfeeding were day 7 “infant feeding difficulty” (adjusted PAR = 32%) and day 14 “milk quantity” (adjusted PAR = 23%). CONCLUSIONS: Breastfeeding concerns are highly prevalent and associated with stopping breastfeeding. Priority should be given to developing strategies for lowering the overall occurrence of breastfeeding concerns and resolving, in particular, infant feeding and milk quantity concerns occurring within the first 14 days postpartum.

Effects of exercise on plasma lipids and metabolism of lactating women.

To examine the effects of exercise on plasma lipids and metabolism during lactation, sedentary, exclusively breast-feeding women were randomly assigned to an exercise (E) or control (C) group at 6-8 wk postpartum. E subjects performed aerobic exercise 45 min.d-1, 5 d.wk-1, for 12 wk. Resting metabolic rate (RMR), energy expenditure, body composition, and dietary intake were measured at 6-8, 12-14, and 18-20 wk postpartum. Maximum oxygen uptake (VO2max), postprandial insulin, glucose, and thermic response, and plasma lipid levels were measured at 6-8 and 18-20 wk. VO2max increased by 25% vs 5% in the E vs the C group, respectively (P < 0.0001). RMR was similar between groups and did not change over time. Weight and percent body fat declined (P < 0.01) during the study, but there was no difference between E and C groups. Exercise marginally increased high-density lipoprotein cholesterol levels (P < 0.08), but did not affect other lipid concentrations. Insulin response decreased as VO2max increased (P = 0.05). There was no effect of time or group on glucose or thermic response. Exercise improves cardiovascular fitness during lactation, but does not increase the rate of postpartum weight loss.