Sexually Dimorphic Associations between Maternal Factors and Human Milk Hormonal Concentrations

Milk metabolite composition of a semi-captive population of Asian elephants

Lack of maternal milk commonly leads to Asian elephant calves' death in captivity. Currently, available supplements seem inefficient. Hence, we aimed at characterizing the composition of Asian elephant milk to provide information on calves' nutritional needs. Seventy milk samples from 22 Asian elephants living in semi-captivity in their natural environment in Myanmar were collected. Samples were analysed through various techniques including liquid chromatography tandem mass spectrometry, gas chromatography-flame ionization detector, and bicinchoninic acid assay to determine total protein content and various metabolites. Associations with lactation stage (months postpartum) were investigated through repeated measure mixed models. We identified 160 compounds: 22 amino acids, 12 organic acids of the tricarboxylic acid cycle, 27 fatty acids, 15 acyl-carnitines and 84 phospholipids. The milk contained substantial amounts of free glutamate (median: 1727.9, interquartile range (IQR): 1278.4 µmol l-1) and free glycine (2541.7, IQR: 1704.1 µmol l-1). The fatty acid profile was mostly constituted by saturated fatty acids, particularly capric acid (40.1, IQR: 67.3 g l-1). Milk samples also contained high amounts of carnitines, phospholipids and organic acids. The wide array of metabolites identified and quantified, some of which present high concentrations in the milk from this species as opposed to other species, suggests underpinning physiological functions that might be crucial for the survival of Asian elephant calves.

Investigation of Relationships between Intakes of Human Milk Total Lipids and Metabolic Hormones and Infant Sex and Body Composition

Human milk (HM) composition, including metabolic hormones and lipids, is influenced by various factors, including lactation stage and, potentially, infant sex, which may affect infant body composition (BC) development. We aimed to: (a) characterize the longitudinal concentration and intake profiles of HM leptin, adiponectin, insulin, and total lipids; (b) determine if their concentrations and intakes differ by infant sex; and (c) explore the intakes relationships with the development of infant BC. Milk samples (n = 501) were collected from 82 mother-infant dyads during the first 6 months postpartum. Infant 24 h HM intake was measured, and the average cumulative HM component intakes were calculated. The statistical analysis used linear mixed modeling. Intakes of HM leptin, adiponectin, insulin, and total lipids increased to 1 month postpartum and then remained stable. HM intake and total lipids intake but not hormone intakes were positively associated with infant BC (fat-free mass, fat-free mass index, fat mass, fat mass index, percentage fat mass, and fat mass to fat-free mass ratio). HM component concentrations and intakes did not differ by sex. These findings advance our understanding of the temporal nature of HM components, emphasizing the role of infant 24 h HM and total lipids intake in development of infant lean and adipose tissue.

Gestational Diabetes Mellitus and Colostral Appetite-Regulating Adipokines

Gestational diabetes mellitus (GDM) is a complex metabolic disorder that has short- and long-term effects on maternal and offspring health. This study aimed to assess the impact of maternal hyperglycemia severity, classified as GDM-G1 (diet treatment) and GDM-G2 (insulin treatment) on colostral appetite-regulating molecules. Colostrum samples were collected from hyperglycemic (N = 30) and normoglycemic (N = 21) mothers, and the concentrations of milk hormones were determined by immunoenzymatic assay. A difference was found for milk ghrelin, but not for molecules such as adiponectin, leptin, resistin, or IGF-I levels, in relation to maternal hyperglycemia. The colostral ghrelin in the GDM-G1 cohort (0.21 ng/mL) was significantly lower than for GDM-G2 (0.38 ng/mL) and non-GDM groups (0.36 ng/mL). However, colostral resistin was higher, but not significantly, for GDM-G1 (13.33 ng/mL) and GDM-G2 (12.81 ng/mL) cohorts than for normoglycemic mothers (7.89 ng/mL). The lack of difference in relation to hyperglycemia for milk leptin, adiponectin, leptin-adiponectin ratio, resistin, and IGF-I levels might be the outcome of effective treatment of GDM during pregnancy. The shift between ghrelin and other appetite-regulating hormones might translate into altered ability to regulate energy balance, affecting offspring's metabolic homeostasis.

Association between maternal metabolic profiles in pregnancy, dietary patterns during lactation and breast milk leptin: a retrospective cohort study

Breast milk leptin plays a potential role in preventing childhood obesity. However, the associations of breast milk leptin with maternal metabolism in pregnancy and dietary patterns during lactation are still unclear. We aimed to explore associations of breast milk leptin with maternal metabolic profiles in pregnancy and dietary patterns during lactation. A total of 332 participants were recruited for this retrospective cohort study. Breast milk samples were collected at approximately 6 weeks postpartum. Breast milk leptin and twenty-three metabolic profiles in pregnancy were measured in this study. A semi-quantitative FFQ was used to gather dietary information during lactation. Both principal component analysis and the diet balance index were used to derive dietary patterns. Among twenty-three maternal metabolic profiles, maternal serum glucose (β = 1·61, P = 0·009), γ-glutamyl transferase (β = 0·32, P = 0·047) and albumin (β = -2·96, P = 0·044) in pregnancy were correlated with breast milk leptin. All dietary patterns were associated with breast milk leptin. Given the joint effects of maternal metabolism in pregnancy and dietary patterns during lactation, only diet quality distance was significantly associated with leptin concentrations in breast milk (low level v. almost no diet problem: β = -0·46, P = 0·011; moderate/high level v. almost no diet problem: β = -0·43, P = 0·035). In conclusion, both maternal metabolism in pregnancy and dietary patterns during lactation were associated with breast milk leptin. Maternal diet balance during lactation was helpful to improve breast milk leptin concentration.

Does human milk composition predict later risk of obesity? A systematic review

BACKGROUND

Possible mechanisms behind the association of breastfeeding with a lower risk of later obesity are unknown but one possibility is the unique composition of human milk. Here, we systematically reviewed the evidence linking breast-milk macronutrient and hormonal composition with later obesity.

METHODS

We searched 7 databases for studies that included infants predominantly breast-fed for the first 3 months and which analysed associations between a measure of breast-milk composition and later (> 6 months) measures of obesity or body composition.

RESULTS

47 publications were identified for full-text screening, of which 10 were eligible and only 3 found significant associations. Higher leptin concentration in breast milk at age 1 month was associated with lower infant BMI at 12, 18 and 24 months of age (1 study). Higher breast-milk adiponectin concentration at 6 weeks and 4 months were associated with adiposity at age 12 and 24 months (1 study). In 1 study, breast-milk carbohydrate content was positively associated, and fat content negatively associated, with adiposity at age 12 months. No significant associations were found between other hormones or macronutrients in human milk and later risk of obesity or body composition.

CONCLUSIONS

The evidence linking breast-milk composition with later obesity was inconsistent and confined to single, individual studies. Our review highlights the methodological limitations of previous studies and the need for further research in this area.

Potential sex differences in human milk fatty acids and their association with atopic dermatitis: Results of the Ulm SPATZ health study

BACKGROUND

Polyunsaturated fatty acids (PUFAs) in human milk are essential in immune system maturation and might play a role in the development of allergic conditions, such as atopic dermatitis (AD) in infants. Immune system responses are modulated by sex, but data on the sex-specific associations with PUFAs are limited. We therefore explored sex-specific differences in human milk PUFAs and their association with AD up to 2 years.

METHODS

PUFAs were measured in human milk samples from the Ulm SPATZ Health Study at 6 weeks (n = 512) and 6 months (n = 367). Associations with AD up to 2 years were evaluated using crude and multivariable logistic regression. Interactions between infant sex and PUFAs were explored by including the product term.

RESULTS

No significant associations were observed with 6-week data. At 6 months, the median relative proportion of docosahexaenoic acid (DHA) was significantly higher in milk for female than male infants (p = .001). Female infants whose milk was lower in quintile proportions of alpha-linolenic acid (ALA) at 6 months had lower odds of AD compared to males [first vs. fifth quintile OR (95% confidence interval): 0.13 (0.02, 0.66), p = .02]. This interaction was not significant when correcting for multiple testing (α threshold: p = .004). No other statistically significant associations were observed.

CONCLUSION

Individual quintile PUFA proportions in human milk were not associated with AD, overall and in a sex-specific manner. More comprehensive and statistically powered longitudinal studies are needed to determine whether potential sex differences in human milk, if any, could be of clinical relevance for infants including the investigation of mediating factors.

Hormonal regulation of mammary gland development and lactation

Lactation is critical to infant short-term and long-term health and protects mothers from breast cancer, ovarian cancer and type 2 diabetes mellitus. The mammary gland is a dynamic organ, regulated by the coordinated actions of reproductive and metabolic hormones. These hormones promote gland development from puberty onwards and induce the formation of a branched, epithelial, milk-secreting organ by the end of pregnancy. Progesterone withdrawal following placental delivery initiates lactation, which is maintained by increased pituitary secretion of prolactin and oxytocin, and stimulated by infant suckling. After weaning, local cytokine production and decreased prolactin secretion trigger large-scale mammary cell loss, leading to gland involution. Here, we review advances in the molecular endocrinology of mammary gland development and milk synthesis. We discuss the hormonal functions of the mammary gland, including parathyroid hormone-related peptide secretion that stimulates maternal calcium mobilization for milk synthesis. We also consider the hormonal composition of human milk and its associated effects on infant health and development. Finally, we highlight endocrine and metabolic diseases that cause lactation insufficiency, for example, monogenic disorders of prolactin and prolactin receptor mutations, maternal obesity and diabetes mellitus, interventions during labour and delivery, and exposure to endocrine-disrupting chemicals such as polyfluoroalkyl substances in consumer products and other oestrogenic compounds.

The Impact of Gestational Diabetes Mellitus on Human Milk Metabolic Hormones: A Systematic Review

Gestational diabetes mellitus (GDM) is a common pregnancy complication with short- and long-term health consequences for the infant and mother. Breastfeeding is the recommended mode of feeding as it offers an opportunity to reduce the risk of GDM consequences, likely partially mediated through changes in human milk (HM) composition. This review systematically reviewed 12 identified studies that investigated the impact of GDM on concentrations of HM metabolic hormones. Meta-analysis was not possible due to significant heterogeneity in study designs and hormone measurement techniques. The risk of bias was assessed using the National Institute for Clinical Excellence (NICE) tool. The methodological qualities were medium in half of the studies, while 25% (3/12) of studies carried a high risk of bias. Significant relationships were reported between GDM and concentrations of HM ghrelin (3/3 studies), insulin (2/4), and adiponectin (2/6), which may play an integral role in infant growth and development. In conclusion, preliminary evidence suggests that GDM may alter HM metabolic hormone concentrations; however, these relationships may be limited to the early lactation stage.

Infant sex differences in human milk intake and composition from 1- to 3-month post-delivery in a healthy United States cohort

BACKGROUND

Macronutrient composition of human milk differs by infant sex, but few studies have examined sex differences in other milk components, or their potential modification by maternal body mass index (BMI).

AIM

We compared milk intake and human milk hormone and cytokine concentrations at 1- and 3-month post-delivery and tested infant sex by maternal BMI (OW/OB vs. NW) interactions.

SUBJECTS AND METHOD

Data were analysed for 346 mother-infant dyads in the Mothers and Infants Linked for Healthy Growth (MILk) Study at 1- and 3-month post-delivery. Infant milk intake was estimated by the change in infant weight after test feedings. Concentrations of glucose, insulin, leptin, adiponectin, interleukin-6 (IL-6), and C-reactive protein (CRP) were measured using ELISA. Multivariable linear regression and linear mixed models were used to estimate sex main effects and their interaction with maternal BMI.

RESULTS

Mean glucose concentration at 1 month was 2.62 mg/dl higher for male infants, but no difference at 3 months was observed. Milk intake and concentrations for the other milk components were similar for males and females at both time points. Associations with infant sex did not differ significantly by maternal BMI.

CONCLUSIONS

Among healthy United States mother-infant dyads, appetite, and growth-regulating factors in human milk did not differ significantly by infant sex.

Human Milk Metabolic Hormones: Analytical Methods and Current Understanding

Human milk (HM) contains a wide array of peptide hormones including leptin and adiponectin, which are involved in the regulation of infant growth and development. These essential hormones might play an important role in the regulation of metabolic reprogramming of the new-born infant. However, HM hormone studies are sparse and heterogeneous in regard to the study design, sample collection, preparation and analysis methods. This review discussed the limitations of HM hormone analysis highlighting the gaps in pre-analytical and analytical stages. The methods used to quantify HM metabolic hormones (leptin, adiponectin, ghrelin, insulin, obestatin, resistin and apelin) can be classified as immunoassay, immunosensor and chromatography. Immunoassay methods (ELISA and RIA) have been predominantly used in the measurement of these HM hormones. The relative validity parameters of HM hormones analysis are often overlooked in publications, despite the complexity and differences of HM matrix when compared to that of plasma and urine. Therefore, appropriate reports of validation parameters of methodology and instrumentation are crucial for accurate measurements and therefore better understanding of the HM metabolic hormones and their influences on infant outcomes.

Metabolic Hormone Profiles in Breast Milk From Mothers of Moderate-Late Preterm Infants Are Associated With Growth From Birth to 4 Months in a Sex-Specific Manner

Background: Differing environmental conditions experienced by mother-infant dyads may influence composition of the milk received by the infant. As a consequence, diverse milk compositional profiles may contribute to different postnatal outcomes, especially in infants facing adverse perinatal environments. We investigated whether variability in milk concentrations of key metabolic hormones is associated with different growth outcomes in infants born preterm, a perinatal complication known to impact on infant growth. Methods: Human milk samples were collected from 169 mothers of 191 infants enrolled in the DIAMOND trial, a randomized trial of nutrition for moderate-late preterm infants, at 5 and 10 days postpartum and again at 4 months' corrected age and analyzed for leptin, adiponectin and insulin-like growth factor (IGF)-1. Infant weight and body composition were measured at birth, discharge and 4 months' corrected age. Multiple linear regression models were used to examine correlations between milk hormone concentrations, weight z-scores and body composition at discharge and 4 months' corrected age, and weight gain from birth to 4 months' corrected age. Sex-specific interactions were examined. Results: Higher milk IGF-1 concentrations on day 5 after birth were associated with greater infant fat-free mass at 4 months' corrected age. Milk IGF-1 concentrations at 4 months were positively associated with fat mass and fat-free mass at 4 months in boys but not girls. Milk leptin concentrations on day 5 after birth were positively associated with fat mass at discharge from hospital, but negatively associated with fat mass at 4 months' corrected age. No significant association was found for milk adiponectin concentrations. Conclusion: Milk IGF-1 and leptin concentrations in mothers of moderate-late preterm babies are associated with different growth and body composition through to 4 months' corrected age and these associations are often different in boys and girls. The sex-specific effects of nutrient and hormone exposure during early life in preterm infants warrants further investigation to optimize the nutritional care these infants receive, particularly in hospital, where the same nutrition is provided to boys and girls.

Preterm human milk: associations between perinatal factors and hormone concentrations throughout lactation

BACKGROUND

Infants born moderate to late preterm constitute the majority of preterm births, yet guidelines for their nutritional care are unclear. Maternal milk is the most appropriate nutrition for these infants; however, its composition can be influenced by environmental factors. The present study therefore investigated perinatal predictors of human milk composition in a preterm cohort.

METHODS

Milk was collected during the DIAMOND trial (DIfferent Approaches to Moderate and late preterm Nutrition: Determinants of feed tolerance, body composition and development) from 169 mothers of 191 infants at three time-points (5 and 10 days post partum and 4 months' corrected age). Leptin, adiponectin and insulin-like growth factor-1 (IGF-1) were analysed by enzyme-linked immunosorbent assay. Generalised mixed models were used to evaluate associations between milk composition and maternal/infant/perinatal factors.

RESULTS

Most findings were independent of collection time-point. Gestational diabetes was associated with lower adiponectin. Higher adiponectin and lower leptin were associated with higher socioeconomic status, higher maternal education and ability to fully breastfeed at discharge from hospital. Higher leptin was associated with high perceived stress during hospital admission. Milk IGF-1 displayed sex-specific patterns in association with maternal social deprivation.

CONCLUSION

Maternal, infant and environmental factors during the perinatal period were associated with milk compositional profiles throughout lactation. Further clinical trials should investigate the impact of such changes in terms of long-term infant outcomes.

IMPACT

Human milk is the best nutrition for the infant. However, its composition may be susceptible to alterations determined by pathological conditions mother and infant may face throughout pregnancy and in the perinatal period. This study found that perinatal factors are associated with human milk composition from early to late lactation. If human milk composition throughout lactation is "programmed" during pregnancy or early lactation, infants who were exposed in utero to environmental insults may still be exposed to them during lactation. The impact of human milk compositional alteration on infant growth following perinatal pathological events requires further investigation.

The need to study human milk as a biological system

Critical advancement is needed in the study of human milk as a biological system that intersects and interacts with myriad internal (maternal biology) and external (diet, environment, infections) factors and its plethora of influences on the developing infant. Human-milk composition and its resulting biological function is more than the sum of its parts. Our failure to fully understand this biology in a large part contributes to why the duration of exclusive breastfeeding remains an unsettled science (if not policy). Our current understanding of human-milk composition and its individual components and their functions fails to fully recognize the importance of the chronobiology and systems biology of human milk in the context of milk synthesis, optimal timing and duration of feeding, and period of lactation. The overly simplistic, but common, approach to analyzing single, mostly nutritive components of human milk is insufficient to understand the contribution of either individual components or the matrix within which they exist to both maternal and child health. There is a need for a shift in the conceptual approach to studying human milk to improve strategies and interventions to support better lactation, breastfeeding, and the full range of infant feeding practices, particularly for women and infants living in undernourished and infectious environments. Recent technological advances have led to a rising movement towards advancing the science of human-milk biology. Herein, we describe the rationale and critical need for unveiling the multifunctionality of the various nutritional, nonnutritional, immune, and biological signaling pathways of the components in human milk that drive system development and maturation, growth, and development in the very early postnatal period of life. We provide a vision and conceptual framework for a research strategy and agenda to change the field of human-milk biology with implications for global policy, innovation, and interventions.

Do preterm girls need different nutrition to preterm boys? Sex-specific nutrition for the preterm infant

Boys born preterm are recognised to be at higher risk of adverse outcomes than girls born preterm. Despite advances in neonatal intensive care and overall improvements in neonatal morbidity and mortality, boys born preterm continue to show worse short- and long-term outcomes than girls. Preterm birth presents a nutritional crisis during a critical developmental period, with postnatal undernutrition and growth-faltering common complications of neonatal intensive care. Furthermore, this preterm period corresponds to that of rapid in utero brain growth and development, and the developmental window relating to foetal programming of adult non-communicable diseases, the prevalence of which are associated both with preterm birth and sex. There is increasing evidence to show that from foetal life, boys and girls have different responses to maternal nutrition, that maternal breastmilk composition differs based on foetal sex and that early neonatal nutritional interventions affect boys and girls differently. This narrative review examines the evidence that sex is an important moderator of the outcomes of preterm nutrition intervention, and describes what further knowledge is required before providing nutrition intervention for infants born preterm based on their sex. IMPACT: This review examines the increasing evidence that boys and girls respond differently to nutritional stressors before birth, that maternal breastmilk composition differs by foetal sex and that nutritional interventions have different responses based on infant sex. Boys and girls born preterm are given standard nutritional support which does not take infant sex into account, and few studies of neonatal nutrition consider infant sex as a potential mediator of outcomes. By optimising early nutrition for boys and girls born preterm, we may improve outcomes for both sexes. We propose future studies of neonatal nutritional interventions should consider infant sex.

Exclusive Breastfeeding Predicts Higher Hearing-Language Development in Girls of Preschool Age

Cognitive disorders are increasing in prevalence. Nutritional or metabolic stressors during early life, and female sex, are predisposing conditions towards the development of cognitive diseases, including Alzheimer’s disease. Though there is evidence that breastfeeding may play a beneficial role in children’s neurocognitive development, the literature remains controversial. In this study we aimed at assessing the association between exclusive breastfeeding and children’s cognitive development from six months to five years of age, addressing sex differences. In 80 mother-child pairs from the Pisa birth cohort (PISAC), we measured cognitive development in groups of children of 6, 12, 18, 24, 36, and 60 months by Griffiths Mental Development Scales, parents’ intelligence quotient (IQ) by Raven’s progressive matrices, and maternal and infants’ anthropometric parameters. We found that exclusive breastfeeding was associated with higher hearing-language development in five years old girls, independent of maternal IQ, age and BMI (body mass index). Exclusive breastfeeding in the first three months of life seemed sufficient to establish this positive relationship. In conclusion, our data indicate that exclusive breastfeeding is a positive predictor of cognitive development in preschool-age girls, paving the way for the implementation of sex-specific cognitive disease risk detection and prevention strategies from early life. Further studies are warranted to explore causality and longer term effects.

Growth Factor Concentrations in Human Milk Are Associated With Infant Weight and BMI From Birth to 5 Years

Background: Human milk bioactives may play a role in infant health and development. Although the variability in their concentrations in milk is well-established, the impact of differential milk profiles on infant growth outcomes remains unclear. Thus, the aim of the present study was to investigate whether different concentrations of metabolic hormones are associated with different weight and BMI in infants beyond the first year of life. Methods: Milk samples at 2.6 (±0.4) months after birth and anthropometric measures at 13 months, 2, 3, and 5 years were collected as part of the Finnish STEPS cohort study from 501 mothers and the respective 507 infants. Leptin, adiponectin, insulin-like growth factor (IGF)-1 and cyclic glycine-proline (cGP) in milk were analyzed. Multiple regression models and a repeated measures mixed model were used to examine associations between milk hormone concentrations and weight and BMI z-scores across time, at each time-point, and weight gain from birth to each follow-up visit. All models were corrected for birth weight, infant sex, duration of exclusive and total breastfeeding, time of introduction of solid foods and maternal pre-pregnancy BMI. Results: Higher milk IGF-1 was associated with higher weight at 13 months (p = 0.004) but lower weight at 3 (p = 0.011) and 5 years of age (p = 0.049). Higher cGP was associated with lower weight across the 5 years (p = 0.019) but with higher BMI at 5 years (p = 0.021). Leptin and adiponectin did not display associations with infant growth at this time. Sex interactions were also absent. Conclusions: Our results suggest that the interplay between human milk-borne IGF-1 and cGP is similar to that reported in other mammals and may have an important role in defining infant growth trajectories beyond the first year of life. Further research should explore the determinants and origins of these milk-borne compounds and evaluate their effect on infant growth and metabolism.

Cholinergic-pathway-weakness-associated pancreatic islet dysfunction: a low-protein-diet imprint effect on weaned rat offspring

Currently, metabolic disorders are one of the major health problems worldwide, which have been shown to be related to perinatal nutritional insults, and the autonomic nervous system and endocrine pancreas are pivotal targets of the malprogramming of metabolic function. We aimed to assess glucose–insulin homeostasis and the involvement of cholinergic responsiveness (vagus nerve activity and insulinotropic muscarinic response) in pancreatic islet capacity to secrete insulin in weaned rat offspring whose mothers were undernourished in the first 2 weeks of the suckling phase. At delivery, dams were fed a low-protein (4% protein, LP group) or a normal-protein diet (20.5% protein, NP group) during the first 2 weeks of the suckling period. Litter size was adjusted to six pups per mother, and rats were weaned at 21 days old. Weaned LP rats presented a lean phenotype (P < 0.01); hypoglycaemia, hypoinsulinaemia and hypoleptinaemia (P < 0.05); and normal corticosteronaemia (P > 0.05). In addition, milk insulin levels in mothers of the LP rats were twofold higher than those of mothers of the NP rats (P < 0.001). Regarding glucose–insulin homeostasis, weaned LP rats were glucose-intolerant (P < 0.01) and displayed impaired pancreatic islet insulinotropic function (P < 0.05). The M3 subtype of the muscarinic acetylcholine receptor (M3mAChR) from weaned LP rats was less responsive, and the superior vagus nerve electrical activity was reduced by 30% (P < 0.01). A low-protein diet in the suckling period malprogrammes the vagus nerve to low tonus and impairs muscarinic response in the pancreatic β-cells of weaned rats, which are imprinted to secrete inadequate insulin amounts from an early age.