Associations Among Maternal Adiposity, Insulin, and Adipokines in Circulation and Human Milk

The association between maternal factors and milk hormone concentrations: a systematic review

Background

Breast milk is the gold standard for infant feeding. It is a dynamic biological fluid rich in numerous bioactive components. Emerging research suggests that these components, including hormones, may serve as signals between mother and offspring. From an evolutionary perspective, maternal hormonal signals could allow co-adaptation of maternal and offspring phenotype, with implications for their Darwinian fitness. However, a series of steps need to be considered to establish the role of a component as a signal and this systematic review focuses on one step: 'Do maternal factors influence the concentration of milk hormones?'

Objective

To systematically review human studies which analyze the association between maternal factors and the concentration of hormones in breast milk.

Methods

Three databases were searched for studies reporting the association of maternal factors including body mass index (BMI), weight, fat mass, age, ethnicity, smoking with hormones such as adiponectin, leptin, insulin, ghrelin, and cortisol in breast milk.

Results

Thirty-three studies were eligible for inclusion. Maternal BMI was positively associated with milk leptin (20/21 studies) and with milk insulin (4/6 studies). Maternal weight also displayed a positive correlation with milk leptin levels, and maternal diabetes status was positively associated with milk insulin concentrations. Conversely, evidence for associations between maternal fat mass, smoking, ethnicity and other maternal factors and hormone levels in breast milk was inconclusive or lacking.

Conclusion

Current evidence is consistent with a signaling role for leptin and insulin in breast milk, however other steps need to be investigated to understand the role of these components as definitive signals. This review represents a first step in establishing the role of signaling components in human milk and highlights other issues that need to be considered going forward.

Comparison of the Effect of Direct Breastfeeding, Expressed Human Milk, and Infant Formula Feeding on Infant Weight Trajectories: A Systematic Review

Background: Formula and breastfeeding are known factors associated with infant weight trajectories. Evidence exploring the effect of expressed human milk feeding on infant weight in the community setting has not been well synthesized. Objectives: This systematic review examined (1) weight changes among infants fed expressed human milk and (2) differences in weight change between infants fed expressed human milk and infants fed at the breast or infant formula via bottle. Methods: A comprehensive search of the literature was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The quality of each study was appraised using the Joanna Briggs Critical Appraisal Tools. Results: A total of six studies met the eligibility criteria and included a total of 5,152 infants. The within-subject analysis identified only 31 infants strictly or predominantly fed expressed human milk. The between-subject analysis comparing expressed human milk feeding to the available comparison groups (formula-fed or direct at the breastfed) revealed that higher weight gains were observed in the weight trajectories among infants in the bottle or formula-fed conditions in four of the six included studies. Conclusions: Findings from the few studies included in this review found a difference in the infant weight gain patterns among expressed human milk-fed infants when compared with their respective feeding groups (directly breastfed or formula-fed). Further research is needed to corroborate these findings and elucidate the clinical significance of the differences in weight gain patterns observed across infant feeding groups.

Bioactive peptides in preterm human milk: Impact of maternal characteristics and their association to neonatal outcomes

Human milk adipokines in term babies seem partially determined by maternal factors and affect infant's development. We aimed to describe bioactive peptide concentration in very preterm human milk and associations to maternal characteristics and postnatal growth. Mothers delivering ≤32 weeks of gestation and their infant/s were recruited. At 4 weeks of lactation, an aliquot of 24-h-pooled milk was collected for exclusively breastfeeding dyads. Insulin, leptin, adiponectin, and milk fat globule epidermal growth factor-8 (MFG-E8) were measured by enzyme-linked immunoabsorbent assay in skimmed milk. One hundred mothers (28.8 ± 2.3 weeks at delivery) provided a milk sample. Milk insulin was related to gestational age, pre-pregnancy body mass index (BMI), and galactagogue treatment (final model: adjusted R2 : 0.330, p < 0.0001; adjusted β coefficients: galactagogue treatment: 0.348, p 0.001; pre-pregnancy BMI: 0.274, p 0.009; gestational age: -0.290, p 0.007). Adiponectin was higher in mothers with gestational diabetes (30.7 ± 6.5 vs. 24.8 ± 8 ng/mL, p 0.044). Leptin was associated with pre-pregnancy BMI (Spearman's ρ: 0.648, p < 0.0001) and MFG-E8 to presence of labor and multiple pregnancy (final linear regression model, R2 : 0.073, p 0.028, adjusted β coefficients: presence of labor -0.229, p 0.050; twins: -0.192, p 0.099). Milk adiponectin was associated with a greater decrease in length z-scores from birth to 28 days (Pearson's r: -0.225, p 0.032) and to discharge (Pearson's r: -0.290, p 0.003). Milk MFG-E8 was lower in milk of mothers whose babies experienced late-onset sepsis (13.3 ± 5.8 vs. 16.8 ± 6.3 μg/mL, p 0.023). Adipokines levels in preterm human milk are partially related to maternal metabolic status. Milk peptide concentration associates with early neonatal growth trajectories.

Leptin receptor expression in blood mononuclear cells of lactating women is associated with infant body weight: Potential role as a molecular biomarker

BACKGROUND

Molecular biomarkers of maternal leptin resistance associated with infant weight are needed.

OBJECTIVES

To evaluate gene expression of leptin receptor (LEPR), suppressor of cytokine signalling 3 (SOCS3) and insulin receptor in peripheral blood mononuclear cells (PBMCs) of lactating women and their relationship with infant body weight and adiposity.

METHODS

At day 10 postpartum, maternal gene expression in PBMCs as well as leptin and insulin concentrations in plasma and milk were assessed (n = 68). Infant weight and BMI z-scores, skinfolds and arm circumference were obtained at 10 days and/or at 3 months old.

RESULTS

In mothers with pre-pregnancy overweight or obesity (OW/OB), LEPR expression was reduced (p = 0.013) whereas plasma and milk leptin and milk insulin concentrations were elevated. LEPR expression was positively related with infant weight z-score (Beta (95% CI): 0.40 (0.17, 0.63), p = 0.001) but not with leptin concentrations. SOCS3 expression was positively related with infant weight z-score (Beta (95% CI): 0.28 (0.04, 0.51), p = 0.024) and arm circumference (Beta (95% CI): 0.57 (0.32, 0.82), p < 0.001). Relationships remained significant after adjusting for maternal and infant confounders.

CONCLUSIONS

LEPR and SOCS3 gene expression in PBMCs are novel maternal molecular biomarkers that reflect leptin resistance and are associated with infant body weight and adiposity.

Maternal Protein Restriction in Rats Alters Postnatal Growth and Brain Lipid Sensing in Female Offspring

Perinatal nutrition is a key player in the susceptibility to developing metabolic diseases in adulthood, leading to the concept of "metabolic programming". The aim of this study was to assess the impact of maternal protein restriction during gestation and lactation on glucose homeostasis and eating behaviour in female offspring. Pregnant rats were fed a normal or protein-restricted (PR) diet and followed throughout gestation and lactation. Body weight, glucose homeostasis, and eating behaviour were evaluated in offspring, especially in females. Body weight gain was lower in PR dams during lactation only, despite different food and water intakes throughout gestation and lactation. Plasma concentration of leptin, adiponectin and triglycerides increased drastically before delivery in PR dams in relation to fat deposits. Although all pups had identical birth body weight, PR offspring body weight differed from control offspring around postnatal day 10 and remained lower until adulthood. Offspring glucose homeostasis was mildly impacted by maternal PR, although insulin secretion was reduced for PR rats at adulthood. Food intake, satiety response, and cerebral activation were examined after a lipid preload and demonstrated some differences between the two groups of rats. Maternal PR during gestation and lactation does induce extrauterine growth restriction, accompanied by alterations in maternal plasma leptin and adiponectin levels, which may be involved in programming the alterations in eating behaviour observed in females at adulthood.

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.

Associations between maternal adiposity and appetite-regulating hormones in human milk are mediated through maternal circulating concentrations and might affect infant outcomes

Background

Appetite-regulating hormones (ARH) in human milk (HM) are suggested to affect infants’ milk intake and possibly infant growth. Maternal adiposity might contribute to higher levels of ARH in HM, either from the mammary gland or from raised circulating levels due to higher adiposity. Counterfactual-based mediation analysis can define indirect and direct effects between HM ARH and maternal and infant factors, and might be an important tool when investigating the mother-milk-infant triad.

Objective

We aim to investigate whether potential associations between (1) maternal adiposity and HM ARH and (2) HM ARH and infant milk intake and growth are mediated through maternal and infant plasma ARH, respectively.

Materials and methods

Maternal and infant anthropometry and body composition, HM and blood samples were collected from 223 mother-infant dyads participating in the Mother, Infant and Lactation Quality study at three postpartum visits from 1 to 8.49 months. Leptin, insulin and adiponectin were analyzed using immunoassays. Mediation analyses using linear mixed-effect models were applied to investigate the direct and indirect effects through maternal and infant plasma hormone concentrations.

Results

A positive association between maternal body-mass-index (BMI) and HM leptin was mediated by maternal plasma leptin by 29% when fixing BMI to < 25 kg/m², and through 51% when fixing BMI to ≥ 25 kg/m² (p_interaction < 0.01). There was no mediated effect through plasma insulin in the association between BMI and HM insulin (p = 0.068). We found negative and positive associations between HM insulin and total milk intake and infant weight, respectively, however, these diminished in mediation analyses with reduced sample sizes.

Conclusion

Our main results suggest that the association between maternal adiposity and HM leptin was mediated through circulating leptin to a stronger degree for mothers with overweight compared to mothers with normal-weight. This indicates that excess maternal adiposity, and the resulting rise of circulating leptin and possible concomitant low-grade inflammation, may be reflected in HM composition.

Clinical trials registry number

NCT03254329.

Influence of Maternal Body Fat on Levels of Insulin, Insulin-Like Growth Factor-1, and Obestatin

BACKGROUND

Insulin, insulin-like Growth Factor-1 (IGF-1), and obestatin in human milk originate from the circulation. There is also limited knowledge about the influence of body fat on the levels of these hormones in human milk.

RESEARCH AIM

To determine (1) the influence of body fat on levels of insulin, IGF-1, and obestatin in human milk and serum/plasma during the postpartum period; (2) the changes in the levels of these hormones in human milk and serum/plasma postpartum; and (3) the presence of IGF-1 mRNA in human milk.

METHODS

In this prospective, longitudinal, observational cohort study, levels of insulin, IGF-1, and obestatin were measured up to 30 days postpartum in milk and serum/plasma of 58 participants with adequate (≤ 32%) or excess (> 32%) total body fat determined by electrical bioimpedance. Student's t test and repeated-measures analysis of variance were used to evaluate the differences between groups. Pearson's test was used to analyze the associations.

RESULTS

The milk from participants with excess body fat had higher insulin and IGF-1 levels and lower obestatin levels than that of participants with adequate body fat at 3-7, 14-15, and 30 days postpartum (adjusted p < .001). The levels of insulin, IGF-1, and obestatin were significantly higher in human milk than in serum/plasma (p < .05) and correlated with maternal body fat (p < .001).

CONCLUSIONS

Maternal body fat was associated with elevated insulin and IGF-1 levels and decreased obestatin levels in human milk up to 30 days postpartum.

Leptin Levels of the Perinatal Period Shape Offspring's Weight Trajectories through the First Year of Age

Background: Leptin is a hormone regulating lifetime energy homeostasis and metabolism and its concentration is important starting from prenatal life. We aimed to investigate the association of perinatal leptin concentrations with growth trajectories during the first year of life. Methods: Prospective, longitudinal study, measuring leptin concentration in maternal plasma before delivery, cord blood (CB), and mature breast milk and correlating their impact on neonate’s bodyweight from birth to 1 year of age, in 16 full-term (FT), 16 preterm (PT), and 13 intrauterine growth-restricted (IUGR) neonates. Results: Maternal leptin concentrations were highest in the PT group, followed by IUGR and FT, with no statistical differences among groups (p = 0.213). CB leptin concentrations were significantly higher in FT compared with PT and IUGR neonates (PT vs. FT; IUGR vs. FT: p < 0.001). Maternal milk leptin concentrations were low, with no difference among groups. Maternal leptin and milk concentrations were negatively associated with all the neonates’ weight changes (p = 0.017 and p = 0.006), while the association with CB leptin was not significant (p = 0.051). Considering each subgroup individually, statistical analysis confirmed the previous results in PT and IUGR infants, with the highest value in the PT subgroup. In addition, this group’s results negatively correlated with CB leptin (p = 0.026) and showed the largest % weight increase. Conclusions: Leptin might play a role in neonatal growth trajectories, characterized by an inverse correlation with maternal plasma and milk. PT infants showed the highest correlation with hormone levels, regardless of source, seeming the most affected group by leptin guidance. Low leptin levels appeared to contribute to critical neonates’ ability to recover a correct body weight at 1 year. An eventual non-physiological “catch-up growth” should be monitored, and leptin perinatal levels may be an indicative tool. Further investigations are needed to strengthen the results.

Century Wide Changes in Macronutrient Levels in Indian Mothers’ Milk: A Systematic Review

The purpose of this systematic review was to understand Indian mothers’ milk composition and report changes in it over the past 100 years. A review was conducted in accordance with PRISMA and registered with PROSPERO (CRD42022299224). All records published between 1921 and 2021 were identified by searching databases Google Scholar, ResearchGate, PubMed, and the Cochrane Database of Systematic Reviews. All observational, interventional, or supplementation studies reporting macronutrients (protein, fat, lactose) in milk of Indian mothers, delivering term infants, were included. Publications on micronutrients, preterm, and methods were excluded. Milk was categorized into colostrum, transitional, and mature. In all, 111 records were identified, of which 34 were included in the final review. Fat ranged from 1.83 to 4.49 g/100 mL, 2.6 to 5.59 g/100 mL, and 2.77 to 4.78 g/100 mL in colostrum, transitional, and mature milk, respectively. The protein was higher in colostrum (1.54 to 8.36 g/100mL) as compared to transitional (1.08 to 2.38 g/100 mL) and mature milk (0.87 to 2.33 g/100 mL). Lactose was lower in colostrum (4.5–6.47 g/100 mL) as compared to transitional (4.8–7.37 g/100 mL) and mature milk ranges (6.78–7.7 g/100 mL). The older studies (1950–1980) reported higher fat and protein in colostrum as compared to subsequent time points. There were variations in maternal nutritional status, diet, socioeconomic status, and regions along with study design specific differences of time or methods of milk sampling and analysis. Additionally, advancements in methods over time make it challenging to interpret time trends. The need for conducting well-designed, multicentric studies on nutrient composition of Indian mother’s milk using standardized methods of sampling and estimation for understanding the role of various associated factors cannot be undermined.

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.

Importance of Bioactive Substances in Sheep's Milk in Human Health

Sheep's milk is an important source of bioactive substances that have health-promoting functions for the body. The valuable composition of sheep's milk is due to the high content of fatty acids, immunoglobulins, proteins, hormones, vitamins and minerals. Many biopeptides found in milk have antibacterial, antiviral and anti-inflammatory properties. The bioactive substances of sheep's milk also show anticancer properties. Sheep's milk, thanks to its content of CLA and orotic acid, prevents the occurrence of type 2 diabetes, Alzheimer's disease and cancer. Sheep's milk, as a product rich in bioactive substances, can be used as a medical aid to support the body in the fight against neurological and cancer diseases.