Elizabeth A. Quinn

Field and laboratory methods in human milk research

Human milk is a complex and variable fluid of increasing interest to human biologists who study nutrition and health. The collection and analysis of human milk poses many practical and ethical challenges to field workers, who must balance both appropriate methodology with the needs of participating mothers and infants and logistical challenges to collection and analysis. In this review, we address various collection methods, volume measurements, and ethical considerations and make recommendations for field researchers. We also review frequently used methods for the analysis of fat, protein, sugars/lactose, and specific biomarkers in human milk. Finally, we address new technologies in human milk research, the MIRIS Human Milk Analyzer and dried milk spots, which will improve the ability of human biologists and anthropologists to study human milk in field settings. Am. J. Hum. Biol., 2013.

Predictors of breast milk macronutrient composition in filipino mothers

There is increasing evidence that breastfeeding has long‐term effects on offspring biology and health, which has heightened interest in understanding the extent of variation in breast milk composition and its underlying determinants. Here, we report variation in milk macronutrient composition in a well‐characterized cohort of young Filipino mothers and test underlying maternal predictors of this variation.

Too much of a good thing: Evolutionary perspectives on infant formula fortification in the United States and its effects on infant health

Recently, there has been considerable debate regarding the appropriate amount of iron fortification for commercial infant formula. Globally, there is considerable variation in formula iron content, from 4 to 12 mg iron/L. However, how much fortification is necessary is unclear. Human milk is low in iron (0.2–0.5 mg/L), with the majority of infant iron stores accumulated during gestation. Over the first few months of life, these stores are depleted in breastfeeding infants. This decline has been previously largely perceived as pathological; it may be instead an adaptive mechanism to minimize iron availability to pathogens coinciding with complementary feeding. Many of the pathogens involved in infantile illnesses require iron for growth and replication. By reducing infant iron stores at the onset of complementary feeding, infant physiology may limit its availability to these pathogens, decreasing frequency and severity of infection. This adaptive strategy for iron regulation during development is undermined by the excess dietary iron commonly found in infant formula, both the iron that can be incorporated into the body and the excess iron that will be excreted in feces. Some of this excess iron may promote the growth of pathogenic, iron requiring bacteria disrupting synergistic microflora commonly found in breastfed infants. Evolutionarily, mothers who produced milk with less iron and infants who had decreased iron stores at the time of weaning may have been more likely to survive the transition to solid foods by having limited iron available for pathogens. Contemporary fortification practices may undermine these adaptive mechanisms and increase infant illness risk. Am. J. Hum. Biol. 26:10–17, 2014.

No evidence for sex biases in milk macronutrients, energy, or breastfeeding frequency in a sample of Filipino mothers.

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.

Maternal Characteristics Associated with Milk Leptin Content in a Sample of Filipino Women and Associations with Infant Weight for Age

Background: Human milk contains many metabolic hormones that may influence infant growth. Milk leptin is positively associated with maternal adiposity and inversely associated with infant growth. Most research has been conducted in populations with higher leptin levels; it is not well understood how milk leptin may vary in lean populations or the associations that reduced leptin may have with infant size for age. It is also largely unknown if associations between maternal body composition and milk leptin persist past 1 year of age. Objectives: We investigated the association between maternal body composition and milk leptin content in a sample of lean Filipino women and the association between milk leptin content and infant size for age. Methods: Milk samples were collected at in-home visits from 113 mothers from Cebu, Philippines. Milk leptin content was measured using EIA techniques; anthropometric data, dietary recalls, and household information were also collected. Results: Mean ± standard deviation (SD) milk leptin in this sample was 300.7 ± 293.6 pg/mL, among the lowest previously reported. Mean ± SD maternal percentage body fat was 24.8% ± 3.5%. Mean ± SD infant age was 9.9 ± 7.0 months, and mean ± SD weight for age z-score was −0.98 ± 1.06. Maternal percentage body fat was a significant, positive predictor of milk leptin content. Milk leptin was a significant, inverse predictor of infant weight and body mass index z-scores in infants 1 year old or younger. Conclusion: The association between maternal body composition, milk leptin, and infant growth persists in mothers with lean body composition. Milk leptin is not associated with growth in older infants.

Milk at altitude: Human milk macronutrient composition in a high‐altitude adapted population of tibetans

OBJECTIVE The physiological challenges of high altitude have led to population-specific patterns of adaptation. These include alterations to child growth and reproduction, including lactation. However, while breastfeeding has been investigated, nothing is known about milk composition in high altitude adapted populations. MATERIALS AND METHODS Here, we investigate milk macronutrient composition, volume, and energy in a sample of 82 Tibetans living at high and low altitude in rural villages (Nubri Valley, Nepal) and at low altitude in Kathmandu, Nepal. Milk samples were collected in the morning using hand expression, frozen, and assayed for fat, protein, and total sugars. Reproductive histories and health recalls were also collected. RESULTS Milk fat averaged 5.2 ±2.0 g/100 mL, milk sugar 7.37 ± 0.49 g/100 mL, and milk protein 1.26 ± 0.35 g/100 mL for a mean energy density of 81.4 ± 17.4 kcal/100 mL. There were no associations between altitude of residence and milk composition; however, overall milk fat was high compared to reference populations. Within the three groups, milk fat was positively associated with infant age (B = 0.103; p < 0.001) and maternal triceps skinfold thickness (B = 0.095; p < 0.01) while milk sugar was significantly and inversely associated with maternal parity and triceps skinfold thickness. DISCUSSION Milk fat, and consequently milk energy, may be increased in high-altitude adapted Tibetans when compared to populations living at low altitude. The association between milk fat and maternal adiposity suggests that milk composition may be sensitive to maternal adiposity in this sample, likely reflecting increased metabolic costs of producing a high-fat milk.

A dose-response relationship between fish consumption and human milk DHA content among Filipino women in Cebu City, Philippines.

Aims:  Human milk is the primary source of docosahexaenoic acid (DHA) for most infants, an important fatty acid for neurological development. Milk DHA is largely incorporated from the maternal diet. Little is known about whether milk DHA varies within populations with differences in maternal fish consumption. Here, we investigate this association in a sample of marginally nourished Filipino women.

Ecological pressures and milk metabolic hormones of ethnic Tibetans living at different altitudes

Abstract 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 age z-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.

Lower hemoglobin levels in first time mothers from Cebu, Philippines.

The association between parity and hemoglobin status in mothers is unclear. Closely spaced pregnancies may predict decreased hemoglobin in women, as these shorter intervals may limit the time available for iron repletion, or maternal age may be associated with general declines in hemoglobin. This study investigated the association between parity and hemoglobin status in a 1‐year birth cohort of mothers from Cebu, Philippines, with variable parities. It was hypothesized that maternal parity would be inversely associated with hemoglobin status and that among multiparous mothers, interbirth interval, and prior breastfeeding duration would be positively associated with hemoglobin level.

Variation among populations in the immune protein composition of mother’s milk reflects subsistence pattern

Abstract Lay Summary Adaptive 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 objectives Mother’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. Methodology Milk 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. Results Both 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 implications Our 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.