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Lay summaryAdaptive immune proteins in mothers' milk are more variable than innate immune proteins across populations and subsistence strategies. These results suggest that the immune defenses in milk are shaped by a mother's environment throughout her life.Background and objectivesMother's milk contains immune proteins that play critical roles in protecting the infant from infection and priming the infant's developing immune system during early life. The composition of these molecules in milk, particularly the acquired immune proteins, is thought to reflect a mother's immunological exposures throughout her life. In this study, we examine the composition of innate and acquired immune proteins in milk across seven populations with diverse disease and cultural ecologies.MethodologyMilk samples (n = 164) were collected in Argentina, Bolivia, Nepal, Namibia, Philippines, Poland and the USA. Populations were classified as having one of four subsistence patterns: urban-industrialism, rural-shop, horticulturalist-forager or agro-pastoralism. Milk innate (lactalbumin, lactoferrin and lysozyme) and acquired (Secretory IgA, IgG and IgM) protein concentrations were determined using triple-quadrupole mass spectrometry.ResultsBoth innate and acquired immune protein composition in milk varied among populations, though the acquired immune protein composition of milk differed more among populations. Populations living in closer geographic proximity or having similar subsistence strategies (e.g. agro-pastoralists from Nepal and Namibia) had more similar milk immune protein compositions. Agro-pastoralists had different milk innate immune protein composition from horticulturalist-foragers and urban-industrialists. Acquired immune protein composition differed among all subsistence strategies except horticulturist-foragers and rural-shop.Conclusions and implicationsOur results reveal fundamental variation in milk composition that has not been previously explored in human milk research. Further study is needed to understand what specific aspects of the local environment influence milk composition and the effects this variation may have on infant health outcomes.

The widespread use of breast pumps in the United States is a recent phenomenon that is reshaping how individuals understand and perceive lactation. In the 1990s, adequacy of milk supply was primarily measured indirectly by infant weight gain and/or diapers; now >95% of all lactating persons in the United States use breast pumps and are seeing their milk regularly. How seeing milk impacts the perception of lactation sufficiency is an important area of research. Research aim/question : To understand personal and intersubjective influences of seeing expressed human milk on perceptions of milk supply among participants who express milk for their infants. We surveyed 805 lactating participants from the United States about their pumping practices using an online survey. Participants described pumping practices, milk output, and beliefs. They were then randomized to view one of three photographs of expressed milk (<2 oz, 4 oz, >6oz) and asked to imagine they had just pumped that amount and provide a written response; this created 4 exposure groups (2 increase and 2 decrease) and a control group (no difference). Participants randomized to a higher volume reported more positive feelings and used the terms "good", "great", and "accomplished" to describe emotional responses to output. Participants randomized to lower milk volumes reported more feelings of "bad" or "depressed." A subset of participants reported feeling "annoyed" about small volumes of milk. Participants in this study were very conscious of the volume of milk pumped each session; both increases and decreases were associated with emotional responses that could contribute to decisions about pumping practices, perceived milk supply, and lactation duration. • Milk expression is not a value neutral experience for lactating individuals. • When shown images of pumped milk, individuals misjudged the amount compared to their typical volume. • Individuals viewing larger amounts of milk than typically pumped reported embodied experiences. • Individuals viewing smaller amounts of milk than typically pumped reported both negative and practical responses. • Perceptions of milk supply can no longer assume milk supply is invisible but is highly visual. [ABSTRACT FROM AUTHOR]

Background: Very little is known about how milk hormones, shown to influence growth during infancy, may contribute to patterns of altered growth in high altitude living infants. Aim: This study investigated the association between maternal BMI, the metabolic hormones adiponectin and leptin in human milk and infant weight for agez-scores (WAZ) in Tibetans. Subjects and methods: A sample of 116 mothers and infants (aged 0–36 months) were recruited from two locations: the Nubri Valley, Nepal (rural; altitude = 2400–3900 m) and Kathmandu, Nepal (urban, 1400 m). Milk samples, anthropometrics, biological data and environmental information were collected on mothers and infants. Milk was analysed for leptin and adiponectin. Results: Maternal BMI was significantly associated with milk leptin content, but not adiponectin in either group. In the rural high altitude sample, child WAZ declined with age, but no such decline was seen in the urban sample. Conclusions: Milk leptin and adiponectin were not associated with infant growth in the rural Nubri sample, but were both inversely associated with infant WAZ in the Kathmandu sample. It appears that, in ecologically stressful environments, associations between milk hormones and growth during infancy may not be detectable in cross-sectional studies. [ABSTRACT FROM PUBLISHER]

Prior studies have reported a significant, inverse association between adiponectin in human milk and offspring growth velocity. Less is known about this association in populations characterised by a loss of weight for age z‐scores (WAZs) in early life. We investigated the association between maternal body composition and milk adiponectin in a sample of Filipino mothers. We then tested for an association between milk adiponectin and size for age in their infants. A total of 117 Filipino mothers nursing infants from 0 to 24 months were recruited from Cebu, Philippines. Anthropometrics, interviews and milk samples were collected and analysed using standard protocols. Mean milk adiponectin in this sample was 7.47 ± 5.75 ng mL−1. Mean infant WAZ and weight for length (WLZ) decreased with age. Maternal body composition was not associated with milk adiponectin content. Milk adiponectin had a significant, positive association with infant WAZ and WLZ. Prior reports have found an inverse association between milk adiponectin and infant WAZ. Here, we report that in lean populations with lower milk adiponectin, there is a positive association with infant WAZ, possibly reflecting pleiotropic biological functions of adiponectin for post‐natal growth. This study increases the understanding of normal biological variation in milk adiponectin and the consequences of low levels of milk adiponectin for offspring growth. [ABSTRACT FROM AUTHOR]

ABSTRACT Maternal reproductive investment includes both the energetic costs of gestation and lactation. For most humans, the metabolic costs of lactation will exceed those of gestation. Mothers must balance reproductive investment in any single offspring against future reproductive potential. Among mammals broadly, mothers may differentially invest in offspring based on sex and maternal condition provided such differences investment influence future offspring reproductive success. For humans, there has been considerable debate if there are physiological differences in maternal investment by offspring sex. Two recent studies have suggested that milk composition differs by infant sex, with male infants receiving milk containing higher fat and energy; prior human studies have not reported sex-based differences in milk composition. This study investigates offspring sex-based differences in milk macronutrients, milk energy, and nursing frequency (per 24 h) in a sample of 103 Filipino mothers nursing infants less than 18 months of age. We found no differences in milk composition by infant sex. There were no significant differences in milk composition of mothers nursing first-born versus later-born sons or daughters or between high- and low-income mothers nursing daughters or sons. Nursing frequency also showed no significant differences by offspring sex, sex by birth order, or sex by maternal economic status. In the Cebu sample, there is no support for sex-based differences in reproductive investment during lactation as indexed by milk composition or nursing frequency. Further investigation in other populations is necessary to evaluate the potential for sex-based differences in milk composition among humans. Am J Phys Anthropol 152:209-216, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]