Human milk as "chrononutrition": implications for child health and development

Biological clock and circadian rhythm of breast milk composition

Breast milk provides numerous benefits for both the baby and the mother, making it a unique and valuable food. The World Health Organization and the United Nations International Children's Emergency Found (UNICEF) state that exclusive breastfeeding in the first six months of life is an important strategy for reducing mortality and morbidity in infants. The circadian rhythm formation, which starts in the mother's womb, continues after the baby is born. Breast milk plays an active role in regulating the baby's circadian rhythm through the hormones, basic immune factors and bioactive components it contains, as well as meeting almost all nutritional elements for babies. Since the neural control mechanisms in the newborn are not yet fully developed, breast milk undertakes the task of helping the biological rhythms in the regulation of the infant's sleep-wake cycles, thanks to the circadian rhythm of some elements in its composition. There are studies showing that breast milk contains high levels of cortisol and amino acids that promote activity during the day, while night milk has high levels of melatonin and tryptophan, and micronutrients vary throughout the day. A better understanding of the circadian rhythm displayed by the elements in the composition of breast milk is important for improving maternal and infant health. Since there are many factors affecting the composition of breast milk, it is recommended that breast milk studies should be done on a country or regional basis, and breastfeeding policies can be developed as a result of the results to be obtained.

Melatonin in Human Breast Milk and Its Potential Role in Circadian Entrainment: A Nod towards Chrononutrition?

Breastfeeding is the most appropriate source of a newborn's nutrition; among the plethora of its benefits, its modulation of circadian rhythmicity with melatonin as a potential neuroendocrine transducer has gained increasing interest. Transplacental transfer assures melatonin provision for the fetus, who is devoid of melatonin secretion. Even after birth, the neonatal pineal gland is not able to produce melatonin rhythmically for several months (with an even more prolonged deficiency following preterm birth). In this context, human breast milk constitutes the main natural source of melatonin: diurnal dynamic changes, an acrophase early after midnight, and changes in melatonin concentrations according to gestational age and during the different stages of lactation have been reported. Understudied thus far are the factors impacting on (changes in) melatonin content in human breast milk and their clinical significance in chronobiological adherence in the neonate: maternal as well as environmental aspects have to be investigated in more detail to guide nursing mothers in optimal feeding schedules which probably means a synchronized instead of mistimed feeding practice. This review aims to be thought-provoking regarding the critical role of melatonin in chrononutrition during breastfeeding, highlighting its potential in circadian entrainment and therefore optimizing (neuro)developmental outcomes in the neonatal setting.

Maternal dietary and environmental factors associated with infant circadian rhythm, growth, and temperament: Research protocol for a prospective cohort study

Introduction: Emerging evidence has been explored to determine the factors affecting the development of infant circadian rhythm. While fetal programming happens during the pregnancy period, external environmental cues and infant nutritional programming can have substantial effects on the infant circadian rhythm. Understanding prenatal and postnatal factors determining infant circadian rhythm can improve future interventions in optimizing maternal and infant health. Methods: This is a prospective observational cohort study, targeting 216 pregnant women from government maternity clinics in Kuala Lumpur, Malaysia. Pregnant women will be recruited at third trimester (baseline), and follow up at 3 months, and 6 months. A subsample will be collected for salivary cortisol analysis to determine circadian rhythm of the mother and infant at third trimester and 3 months. Data of eating misalignment, light exposure, chronotype, infant temperament, sleep quality, and mood will be collected via validated questionnaires. Anthropometric data and birth outcomes will be collected from antenatal and postnatal health records. Summary: Studies on infant circadian rhythm development have yet to be explored and established, hence this study presents a novel approach to identify the factors from prenatal to postnatal periods on infant circadian rhythm and its influence on growth and temperament. Findings from this study will provide insights in the critical timing which has larger effects on infant circadian rhythm development for future interventions to be conducted.

Associations of Infant Feeding, Sleep, and Weight Gain with the Toddler Gut Microbiome

This study examines how feeding, sleep, and growth during infancy impact the gut microbiome (GM) in toddlers. The research was conducted on toddlers (n = 36), born to Latina women of low-income with obesity. Their mothers completed retrospective feeding and sleeping questionnaires at 1, 6, and 12 months; at 36 months, fecal samples were collected. Sequencing of the 16S rRNA gene (V4 region) revealed that breastfeeding for at least 1 month and the introduction of solids before 6 months differentiated the GM in toddlerhood (Bray-Curtis, pseudo-F = 1.805, p = 0.018, and pseudo-F = 1.651, p = 0.044, respectively). Sleep had an effect across time; at 1 and 6 months of age, a lower proportion of nighttime sleep (relative to 24 h total sleep) was associated with a richer GM at three years of age (Shannon H = 4.395, p = 0.036 and OTU H = 5.559, p = 0.018, respectively). Toddlers experiencing rapid weight gain from birth to 6 months had lower phylogenetic diversity (Faith PD H = 3.633, p = 0.057). These findings suggest that early life nutrition, sleeping patterns, and growth rate in infancy may influence the GM composition. Further verification of these results with objective sleep data and a larger sample is needed.

Comprehensive review of melatonin as a promising nutritional and nutraceutical supplement

Background

Melatonin is an indoleamine hormone secreted by the pineal gland at night and has an essential role in regulating human circadian rhythms (the internal 24-h clock) and sleep-wake patterns. However, it has recently gained considerable attention for its demonstrated ability in disease management. This review discusses the major biological activities of melatonin, its metabolites as nutritional supplements, and its bioavailability in food sources.

Methods

The information acquisition process involved conducting a comprehensive search across academic databases including PubMed, Scopus, Wiley, Embase, and Springer using relevant keywords. Only the most recent, peer-reviewed articles published in the English language were considered for inclusion.

Results

The molecular mechanisms by which melatonin induces its therapeutic effects have been the subject of various studies.

Conclusion

While melatonin was initially understood to only regulate circadian rhythms, recent studies indicate that it has a far-reaching effect on various organs and physiological systems, such as immunity, cardiovascular function, antioxidant defense, and lipid hemostasis. As a potent antioxidant, anti-cancer, anti-inflammatory, and immunoregulatory agent, multiple therapeutic applications have been proposed for melatonin.

Sampling Procedures for Estimating the Infant Intake of Human Milk Leptin, Adiponectin, Insulin, Glucose, and Total Lipid

Limited attention is given to the efficacy of protocols for the estimation of infant intake of milk components when investigating their impact on infant outcomes. We compared the actual measured intake of human milk components with estimations derived from 15 protocols to determine the most reliable approach for estimating intake of HM leptin, adiponectin, insulin, glucose, and total lipid. Twenty mothers who were 3-5 months postpartum completed a 24 h milk profile study with pre-/post-feed milk samples collection. The true infant intake (control group) based on 24 h milk intake (MI) was compared to estimated infant intakes using concentrations from five sampling protocols that were multiplied by one of true infant MI, considered mean MI (800 mL), or global mean MI (766 mL). The mean measured concentrations of six samples (three sets of pre- and post-feed samples, from morning (06:00-09:00), afternoon (13:00-16:00), and evening (19:00-22:00)) multiplied by the true infant MI, mean considered MI, and global mean MI produced the most accurate estimates of infant intake of these components. Therefore, in the absence of 24 h measurements and sampling, a sampling protocol comprising three sets of pre-/post-feed samples provides the most reliable infant intake estimates of HM leptin, adiponectin, insulin, glucose, and total lipid.

Maternal diet and human milk composition: an updated systematic review

Context

Exclusive breastfeeding for 6 months after birth provides infants with the best start for life. A review by Bravi et al. summarized the importance of maternal diet as a determinant of human milk composition based on data up to 2015, but evidence on nutrient intake level was limited.

Objective

We updated the review by Bravi et al., critically assessed differences in study designs and sampling methods, and graphically visualized trends and associations.

Data sources

PubMed was systematically searched for articles published between January 2015 and March 2021.

Data extraction

Article screening, selection, and data extraction was done by two independent researchers, including a risk of bias assessment based on 11 criteria. Articles were eligible when including: quantitative information, commonly used effect estimates, healthy mother-infant dyads.

Results

Twenty seven observational and five intervention studies were identified (n = 7,138) and combined with results of Bravi et al. Fatty acids were still the most studied human milk components in relation to maternal diet (n = 17 studies) with maternal fish intake being predominantly positively associated with milk ALA (r = 0.28-0.42), DHA (r = 0.24-0.46), and EPA (r = 0.25-0.28) content. PUFAs from diet were generally positively correlated with their concentrations in milk, while SFA intake was negatively associated with several fatty acids in milk. Studies on associations with maternal diet and milk carbohydrates, proteins, vitamins and minerals were limited in number and varied in methods and results.

Conclusion

This updated review shows that evidence on the association between maternal diet and human milk fatty acids is rapidly increasing, but still diversified in methodology and results. Further studies, preferably intervention studies, assessing diet and milk carbohydrates, proteins, vitamins and minerals are needed to be able draw conclusions on the importance of maternal diet for human milk composition as a whole.

Maternal Circadian Disruption from Shift Work and the Impact on the Concentration of Melatonin in Breast Milk

Background and Objective: Melatonin in breast milk exhibits a 24-hour circadian rhythm, present in nighttime breast milk but nearly undetectable in daytime breast milk. Shift work can disrupt the circadian timing of individuals, evident in changes in melatonin in saliva and urine samples. However, it is unknown whether these changes are also reflected in breast milk from a shift working mother. The aim of this study was to investigate whether maternal circadian rhythm disturbance from shift work impacts the melatonin concentration in breast milk. Materials and Methods: Breast milk and saliva samples were collected from 11 shift working mothers at four timepoints across five consecutive days. This included during their day shift or nonworkdays to act as a control, night shift, subsequent night shifts and postnight shift. Where possible, pre- and postfeed collections were also undertaken. Samples were grouped into four-time intervals: 12-6:30 am, 7-11:30 am, 12-6:30 pm, 7-11:30 pm, and melatonin levels (picogram per milliliter) in the breast milk and saliva samples were analyzed. Results: There was a significant decrease in breast milk melatonin (p = 0.026) at the 12-6:30 am time interval on subsequent night shifts, compared with control days. However, there was no overall time and shift type interaction effect (p = 0.70). In addition, no observed difference in melatonin levels was found in saliva samples, or when comparing pre- and postfeed breast milk. Breast milk melatonin however was found to be significantly higher compared with saliva (p > 0.001), at all but one time interval. Conclusion: The findings suggest that there is a potential effect of maternal circadian rhythm disruption from shift work on breast milk melatonin levels. This is an important step in exploring the role of maternal circadian timing and the effect on breast milk composition. Expansion of this research and exploration of other circadian rhythm misalignment sleep disorders on breast milk is highly recommended.

Rapid Versus Slow Cooling Pasteurization of Donor Breast Milk: Does the Cooling Rate Effect Melatonin Reduction?

Background and Objective: There is a question as to whether melatonin levels in breast milk are impacted by the cooling rate postpasteurization. Past research that has used in the Australian donor bank's breast milk Holder Pasteurization technique has reported varying findings regarding melatonin levels postpasteurization. Where breast milk was cooled slowly, a significant reduction in breast milk melatonin levels was observed. Conversely, where a rapid cooling method was used, there was no significant reduction in melatonin levels. The aim of this study was to investigate whether the cooling process between the different pasteurization techniques impact on melatonin levels in breast milk postpasteurization. Materials and Methods: Twenty-seven nighttime breast milk samples were collected, with each sample divided into three; one remained unpasteurized, one was pasteurized and rapidly cooled to 4°C, and the other was pasteurized and cooled slowly to 4°C. Results: Melatonin levels were significantly reduced in both the rapidly cooled and slow cooled breast milk samples when compared to their unpasteurized counterpart (p < 0.001). There was no significant difference in melatonin levels between the two cooling methods (p = 0.91). Conclusion: This study showed that both the rapid and cooling pasteurization processes had a similar reduction in melatonin levels in breast milk. However, even after pasteurization melatonin was still present. Therefore, it is recommended that donor banks still take into consideration circadian timing hormones such as melatonin and the time of day breast milk is expressed.

Effects of the neonatal intensive care environment on circadian health and development of preterm infants

The circadian system in mammals ensures adaptation to the light-dark cycle on Earth and imposes 24-h rhythmicity on metabolic, physiological and behavioral processes. The central circadian pacemaker is located in the brain and is entrained by environmental signals called Zeitgebers. From here, neural, humoral and systemic signals drive rhythms in peripheral clocks in nearly every mammalian tissue. During pregnancy, disruption of the complex interplay between the mother's rhythmic signals and the fetal developing circadian system can lead to long-term health consequences in the offspring. When an infant is born very preterm, it loses the temporal signals received from the mother prematurely and becomes totally dependent on 24/7 care in the Neonatal Intensive Care Unit (NICU), where day/night rhythmicity is usually blurred. In this literature review, we provide an overview of the fetal and neonatal development of the circadian system, and short-term consequences of disruption of this process as occurs in the NICU environment. Moreover, we provide a theoretical and molecular framework of how this disruption could lead to later-life disease. Finally, we discuss studies that aim to improve health outcomes after preterm birth by studying the effects of enhancing rhythmicity in light and noise exposure.

Circadian Variation in Human Milk Hormones and Macronutrients

There is an inadequate understanding of the daily variations in hormones and macronutrients in human milk (HM), and sample collection protocols vary considerably from study to study. To investigate changes in these milk components across 24 h, 22 lactating women collected small milk samples before and after each breastfeed or expression from each breast. Test weighing was used to determine the volume of HM consumed in each feed. The concentrations of leptin, adiponectin, insulin, fat, and glucose were measured, and the intakes were calculated. A linear mixed model was fitted to assess within-feed and circadian variation in HM feed volume and concentration, and intakes of several components. The average infant intake of HM was 879 g/24 h. Significantly higher pre-feed concentrations were found for adiponectin and glucose and lower post-feed concentrations were found for insulin and fat. Significant circadian rhythms were displayed for leptin, adiponectin, insulin, glucose (both concentration and intake), fat concentration, and milk volume. These findings demonstrate the necessity for setting up standardised and rigorous sampling procedures that consider both within-feed and circadian variations in HM components to gain a more precise understanding of the impacts of these components on infant health, growth and development.

Pediatric sleep: current knowledge, gaps, and opportunities for the future

This White Paper addresses the current gaps in knowledge, as well as opportunities for future studies in pediatric sleep. The Sleep Research Society's Pipeline Development Committee assembled a panel of experts tasked to provide information to those interested in learning more about the field of pediatric sleep, including trainees. We cover the scope of pediatric sleep, including epidemiological studies and the development of sleep and circadian rhythms in early childhood and adolescence. Additionally, we discuss current knowledge of insufficient sleep and circadian disruption, addressing the neuropsychological impact (affective functioning) and cardiometabolic consequences. A significant portion of this White Paper explores pediatric sleep disorders (including circadian rhythm disorders, insomnia, restless leg and periodic limb movement disorder, narcolepsy, and sleep apnea), as well as sleep and neurodevelopment disorders (e.g. autism and attention deficit hyperactivity disorder). Finally, we end with a discussion on sleep and public health policy. Although we have made strides in our knowledge of pediatric sleep, it is imperative that we address the gaps to the best of our knowledge and the pitfalls of our methodologies. For example, more work needs to be done to assess pediatric sleep using objective methodologies (i.e. actigraphy and polysomnography), to explore sleep disparities, to improve accessibility to evidence-based treatments, and to identify potential risks and protective markers of disorders in children. Expanding trainee exposure to pediatric sleep and elucidating future directions for study will significantly improve the future of the field.

Parental factors that impact the ecology of human mammary development, milk secretion, and milk composition-a report from "Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN)" Working Group 1

The goal of Working Group 1 in the Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN) Project was to outline factors influencing biological processes governing human milk secretion and to evaluate our current knowledge of these processes. Many factors regulate mammary gland development in utero, during puberty, in pregnancy, through secretory activation, and at weaning. These factors include breast anatomy, breast vasculature, diet, and the lactating parent's hormonal milieu including estrogen, progesterone, placental lactogen, cortisol, prolactin, and growth hormone. We examine the effects of time of day and postpartum interval on milk secretion, along with the role and mechanisms of lactating parent-infant interactions on milk secretion and bonding, with particular attention to the actions of oxytocin on the mammary gland and the pleasure systems in the brain. We then consider the potential effects of clinical conditions including infection, pre-eclampsia, preterm birth, cardiovascular health, inflammatory states, mastitis, and particularly, gestational diabetes and obesity. Although we know a great deal about the transporter systems by which zinc and calcium pass from the blood stream into milk, the interactions and cellular localization of transporters that carry substrates such as glucose, amino acids, copper, and the many other trace metals present in human milk across plasma and intracellular membranes require more research. We pose the question of how cultured mammary alveolar cells and animal models can help answer lingering questions about the mechanisms and regulation of human milk secretion. We raise questions about the role of the lactating parent and the infant microbiome and the immune system during breast development, secretion of immune molecules into milk, and protection of the breast from pathogens. Finally, we consider the effect of medications, recreational and illicit drugs, pesticides, and endocrine-disrupting chemicals on milk secretion and composition, emphasizing that this area needs much more research attention.

Dietary and Complementary Feeding Practices of US Infants, 6 to 12 Months: A Narrative Review of the Federal Nutrition Monitoring Data

Complementary foods and beverages (CFBs) are key components of an infant's diet in the second 6 months of life. This article summarizes nutrition and feeding practices examined by the 2020 Dietary Guidelines Advisory Committees during the CFB life stage. Breastfeeding initiation is high (84%), but exclusive breastfeeding at 6 months (26%) is below the Healthy People 2030 goal (42%). Most infants (51%) are introduced to CFBs sometime before 6 months. The primary mode of feeding (ie, human milk fed [HMF]; infant formula or mixed formula and human milk fed [FMF]) at the initiation of CFBs is associated with the timing of introduction and types of CFBs reported. FMF infants (42%) are more likely to be introduced to CFBs before 4 months compared with HMF infants (19%). Different dietary patterns, such as higher prevalence of consumption and mean amounts, were observed, including fruit, grains, dairy, proteins, and solid fats. Compared with HMF infants of the same age, FMF infants consume more total energy (845 vs 631 kcal) and protein (22 vs 12 g) from all sources, and more energy (345 vs 204 kcal) and protein (11 vs 6 g) from CFBs alone. HMF infants have a higher prevalence of risk of inadequate intakes of iron (77% vs 7%), zinc (54% vs <3%), and protein (27% vs <3%). FMF infants are more likely to have an early introduction (<12 months) to fruit juice (45% vs 20%) and cow's milk (36% vs 24%). Registered dietitian nutritionists and nutritional professionals should consider tailoring their advice to caregivers on dietary and complementary feeding practices, taking into account the primary mode of milk feeding during this life stage to support infants' nutrient adequacy. National studies that address the limitations of this analysis, including small sample sizes and imputed breast milk volume, could refine findings from this analysis.

[Sleep patterns of infants and young children and their association with breastfeeding: a study based on K-means clustering]

OBJECTIVES

To investigate the sleep patterns and characteristics of infants and young children and the association between sleep patterns and breastfeeding.

METHODS

A general information questionnaire, Brief Infant Sleep Questionnaire (BISQ), and a questionnaire on feeding were used to investigate the sleep quality and feeding patterns of 1 148 infants and young children aged 7-35 months. The K-means clustering method was used to identify sleep patterns and characteristics. A multivariate logistic regression analysis was used to investigate the association between sleep patterns and breastfeeding.

RESULTS

Three typical sleep patterns were identified for the 1 148 infants and young children aged 7-35 months: early bedtime and long sleep time; short sleep latency and moderate sleep time; late bedtime, prolonged sleep latency, and insufficient sleep time. The third pattern showed sleep disorders. The multivariate logistic regression analysis showed that compared with formula feeding, exclusive breastfeeding within 6 months after birth reduced the risk of sleep disorder patterns by 69% (OR=0.31, 95%CI: 0.11-0.81). The risk of sleep disorder patterns was reduced by 40% (OR=0.60, 95%CI: 0.38-0.96) in the infants receiving breastfeeding for 4-6 months compared with those receiving breastfeeding for 1-3 months.

CONCLUSIONS

There are different sleep patterns in infants and young children, and breastfeeding can reduce the development of sleep disorder patterns.

Glucocorticoids in preterm human milk

Background

Glucocorticoids (GCs), cortisol and cortisone, are essential regulators of many physiological responses, including immunity, stress and mammary gland function. GCs are present in human milk (HM), but whether maternal and infant factors are associated with HM GC concentration following preterm birth is unclear.

Materials and methods

HM samples were collected on postnatal day 5 and 10 and at 4 months’ corrected age (4m CA) in a cohort of moderate- and late-preterm infants. GCs in HM were measured by liquid chromatography-tandem mass spectrometry. Relationships between GCs in HM and both maternal and infant characteristics were investigated using Spearman’s correlations and linear mixed models.

Results

170 mothers of 191 infants provided 354 HM samples. Cortisol concentrations in HM increased from postnatal day 5–4m CA (mean difference [MD] 0.6 ± 0.1 ng/ml, p < 0.001). Cortisone concentration did not change across lactation but was higher than cortisol throughout. Compared to no antenatal corticosteroid (ANS), a complete course of ANS was associated with lower GC concentrations in HM through to 4m CA (cortisol: MD –0.3 ± 0.1 ng/ml, p < 0.01; cortisone MD –1.8 ± 0.4 ng/ml, p < 0.001). At 4m CA, higher maternal perceived stress was negatively associated with GC concentrations in HM (cortisol adjusted beta-coefficient [aβ] –0.01 ± 0.01 ng/ml, p = 0.05; and cortisone aβ –0.1 ± 0.03 ng/ml, p = 0.01), whereas higher postpartum depression and maternal obesity were associated with lower cortisone concentrations (aβ –0.1 ± 0.04 ng/ml p < 0.05; MD [healthy versus obese] –0.1 ± 0.04 ng/ml p < 0.05, respectively). There was a weak positive correlation between GC concentrations in HM and gestational age at birth (r = 0.1, p < 0.05). Infant birth head circumference z-score was negatively associated with cortisol concentrations (aβ –0.01 ± 0.04 ng/ml, p < 0.05). At hospital discharge, fat-free mass showed a weak positive correlation with cortisol concentrations (r = 0.2, p = 0.03), while fat mass showed a weak negative correlation with cortisone concentrations (r = –0.25, p < 0.001).

Conclusion

The mammary gland appears to protect the infant from cortisol through inactivation into cortisone. Maternal and infant characteristics were associated with concentration of GCs in HM, including ANS, stress and depression scores, obesity, gestational age and infant size. The effects of HM glucocorticoids on long-term health outcomes requires further research.

Metabolomic and exposomic biomarkers of risk of future neurodevelopmental delay in human milk

BACKGROUND

The chemical composition of human milk has long-lasting effects on brain development. We examined the prognostic value of the human milk metabolome and exposome in children with the risk of neurodevelopmental delay (NDD).

METHODS

This retrospective cohort study included 82 mother-infant pairs (40 male and 42 female infants). A total of 59 milk samples were from mothers with typically developing children and 23 samples were from mothers of children at risk. Milk samples were collected before 9 months of age (4.6 ± 2.5 months, mean ± SD). Neurocognitive development was assessed by maternal report at 14.2 ± 3.1 months using the Ages and Stages Questionnaires-2.

RESULTS

Metabolome and exposome profiling identified 453 metabolites and 61 environmental chemicals in milk. Machine learning tools identified changes in deoxysphingolipids, phospholipids, glycosphingolipids, plasmalogens, and acylcarnitines in the milk of mothers with children at risk for future delay. A predictive classifier had a diagnostic accuracy of 0.81 (95% CI: 0.66-0.96) for females and 0.79 (95% CI: 0.62-0.94) for males.

CONCLUSIONS

Once validated in larger studies, the chemical analysis of human milk might be added as an option in well-baby checks to help identify children at risk of NDD before the first symptoms appear.

IMPACT

Maternal milk for infants sampled before 9 months of age contained sex-specific differences in deoxysphingolipids, sphingomyelins, plasmalogens, phospholipids, and acylcarnitines that predicted the risk of neurodevelopmental delay at 14.2 months of age. Once validated, this early biosignature in human milk might be incorporated into well-baby checks and help to identify infants at risk so early interventions might be instituted before the first symptoms appear.

Birth, love, and fear: Physiological networks from pregnancy to parenthood

Pregnancy and childbirth are among the most dramatic physiological and emotional transformations of a lifetime. Despite their central importance to human survival, many gaps remain in our understanding of the temporal progression of and mechanisms underlying the transition to new parenthood. The goal of this paper is to outline the physiological and emotional development of the maternal-infant dyad from late pregnancy to the postpartum period, and to provide a framework to investigate this development using non-invasive timeseries. We focus on the interaction among neuroendocrine, emotional, and autonomic outputs in the context of late pregnancy, parturition, and post-partum. We then propose that coupled dynamics in these outputs can be leveraged to map both physiologic and pathologic pregnancy, parturition, and parenthood. This approach could address gaps in our knowledge and enable early detection or prediction of problems, with both personalized depth and broad population scale.

Development of circadian rest-activity rhythms during the first year of life in a racially diverse cohort

STUDY OBJECTIVES

To describe the development of circadian rest-activity rhythms (CRARs) during infancy in a racially diverse cohort.

METHODS

We studied 414 infants from the Nurture birth cohort (51.2% female, 65.2% Black) who wore actigraphs on their left ankles for 4 days and nights at 3, 6, 9, and 12 months. We quantified CRARs using cosinor and non-parametric circadian rhythm analysis, and investigated change in CRARs over time, comparing 6, 9, and 12 months to CRARs at 3 months. We adjusted for baseline and time-varying covariates and used function-on-scalar regression (FOSR) to identify the specific times of day at which activity changes occurred.

RESULTS

Across the first year, daily mean and peak activity levels and day-to-day activity level regularity increased, and activity level fragmentation and nighttime activity decreased. Only at 9 months, compared to at 3 months, did timing of peak activity levels and the most active periods shift later, while timing of least active periods shifted earlier. FOSR analyses showed that mean activity levels decreased during nighttime hours and increased during daytime hours, with the most pronounced changes at 9 months.

CONCLUSIONS

Among racially diverse infants, CRARs became more robust, stable, and less fragmented over time. Findings suggest the greatest change from 3-month CRARs occurs at 9 months, which may be a key period of CRAR development. This and future research will contribute to our understanding of normative infant CRAR development in diverse populations and enable us to identify infants who may benefit from intervention.

Association Between Exposure to Outdoor Artificial Light at Night and Sleep Disorders Among Children in China

IMPORTANCE

Healthy sleep has an important role in the physical and mental health of children. However, few studies have investigated the association between outdoor artificial light at night (ALAN) and sleep disorders in children.

OBJECTIVE

To explore the associations between outdoor ALAN exposure and sleep disorders in children.

DESIGN, SETTING, AND PARTICIPANTS

This population-based cross-sectional study, part of the National Chinese Children Health Study, was conducted from April 1, 2012, to June 30, 2013, in the first stage and from May 1, 2016, to May 31, 2018, in the second stage in 55 districts of 14 cities in China. This analysis included 201 994 children and adolescents aged 2 to 18 years. Data were analyzed from February 20 to March 21, 2022.

EXPOSURES

Outdoor ALAN exposure (in nanowatts per centimeters squared per steradian) within 500 m of each participant's residential address obtained from the satellite imagery data, with a resolution of approximately 500 m.

MAIN OUTCOMES AND MEASURES

Sleep disorders were measured by the Chinese version of the Sleep Disturbance Scale for Children. Generalized linear mixed models were used to estimate the associations of outdoor ALAN with sleep scores and sleep disorders.

RESULTS

The study included 201 994 children and adolescents (mean [SD] age, 11.3 [3.2] years; 106 378 boys [52.7%]), 7166 (3.5%) of whom had sleep disorder symptoms. Outdoor ALAN exposure of study participants ranged from 0.02 to 113.48 nW/cm2/sr. Compared with the lowest quintile (Q1) of outdoor ALAN exposure, higher quintiles of exposure (Q2-Q5) were associated with an increase in total sleep scores of 0.81 (95% CI, 0.66-0.96) in Q2, 0.83 (95% CI, 0.68-0.97) in Q3, 0.62 (95% CI, 0.46-0.77) in Q4, and 0.53 (95% CI, 0.36-0.70) in Q5. Higher quintiles of exposure were also associated with odds ratios for sleep disorder of 1.34 (95% CI, 1.23-1.45) in Q2, 1.43 (95% CI, 1.32-1.55) in Q3, 1.31 (95% CI, 1.21-1.43) in Q4, and 1.25 (95% CI, 1.14-1.38) in Q5. Similar associations were observed for sleep disorder subtypes. In addition, greater effect estimates were found among children younger than 12 years.

CONCLUSIONS AND RELEVANCE

The findings of this cross-sectional study suggest that sleep disorders are more prevalent among children residing in areas with high levels of outdoor ALAN and the associations are generally stronger in children younger than 12 years. These findings further suggest that effective control of outdoor ALAN may be an important measure for improving the quality of children's sleep.

Cellular and transcriptional diversity over the course of human lactation

Human breast milk (hBM) is a dynamic fluid that contains millions of cells, but their identities and phenotypic properties are poorly understood. We generated and analyzed single-cell RNA-sequencing (scRNA-seq) data to characterize the transcriptomes of cells from hBM across lactational time from 3 to 632 d postpartum in 15 donors. We found that the majority of cells in hBM are lactocytes, a specialized epithelial subset, and that cell-type frequencies shift over the course of lactation, yielding greater epithelial diversity at later points. Analysis of lactocytes reveals a continuum of cell states characterized by transcriptional changes in hormone-, growth factor-, and milk production-related pathways. Generalized additive models suggest that one subcluster, LC1 epithelial cells, increases as a function of time postpartum, daycare attendance, and the use of hormonal birth control. We identify several subclusters of macrophages in hBM that are enriched for tolerogenic functions, possibly playing a role in protecting the mammary gland during lactation. Our description of the cellular components of breast milk, their association with maternal–infant dyad metadata, and our quantification of alterations at the gene and pathway levels provide a detailed longitudinal picture of hBM cells across lactational time. This work paves the way for future investigations of how a potential division of cellular labor and differential hormone regulation might be leveraged therapeutically to support healthy lactation and potentially aid in milk production.

Human milk: From complex tailored nutrition to bioactive impact on child cognition and behavior

Human milk is a highly complex liquid food tailor-made to match an infant's needs. Beyond documented positive effects of breastfeeding on infant and maternal health, there is increasing evidence that milk constituents also impact child neurodevelopment. Non-nutrient milk bioactives would contribute to the (long-term) development of child cognition and behavior, a process termed 'Lactocrine Programming'. In this review we discuss the current state of the field on human milk composition and its links with child cognitive and behavioral development. To promote state-of-the-art methodologies and designs that facilitate data pooling and meta-analytic endeavors, we present detailed recommendations and best practices for future studies. Finally, we determine important scientific gaps that need to be filled to advance the field, and discuss innovative directions for future research. Unveiling the mechanisms underlying the links between human milk and child cognition and behavior will deepen our understanding of the broad functions of this complex liquid food, as well as provide necessary information for designing future interventions.

Chrononutrition and Human Milk

Background

Breastfed infants have a reduced risk of infections and allergies. The study of chrononutrition in human milk seeks to understand the circadian variation of various human milk immune factors.

Methods

Empirical studies on human milk, chrononutrition, and immune factors were searched through PUBMED, Google Scholar, and SCOPUS. Keywords included “chrononutrition,” “breastmilk composition,” “human milk,” “day-night cycles,” “sleep-wake cycles” and the names of various immune factors. After excluding duplicate articles, animal studies, studies looking at other human milk components, studies that did not collect human milk samples over a 24 hour period, and studies that were not in English, eleven studies on the topic remained and ten studies were included in the review. The excluded study had a sample size of two.

Results

This review identified the circadian variation of certain immune factors found in human milk such as antibodies, complement proteins, cytokines, by-products of phagocyte activity, nucleotides, microRNAs, and antioxidants.

Conclusion

The circadian variation observed in some human milk components highlights the unique ability of human milk to vary in composition based on the circadian rhythms of mothers and infants. The limited number of studies makes it difficult to make conclusive recommendations and creates an opportunity for further research in this growing field.

Odor-active volatile compounds in preterm breastmilk

BACKGROUND

Volatile compounds in breastmilk (BM) likely influence flavor learning and, through the cephalic phase response, metabolism, and digestion. Little is known about the volatile compounds present in preterm BM. We investigated whether maternal or infant characteristics are associated with the profile of volatile compounds in preterm BM.

METHODS

Using solid-phase microextraction coupled with gas chromatography/mass spectrometry, we analyzed volatile compounds in 400 BM samples collected from 170 mothers of preterm infants.

RESULTS

Forty volatile compounds were detected, mostly fatty acids and their esters (FA and FAe), volatile organic compounds (VOCs), aldehydes, terpenoids, alcohols, and ketones. The relative concentration of most FA and FAe increased with advancing lactation and were lower in BM of most socially deprived mothers and those with gestational diabetes (p < 0.05), but medium-chain FAs were higher in colostrum compared to transitional BM (p < 0.001). Infant sex, gestational age, and size at birth were not associated with the profile of volatile compounds in preterm BM.

CONCLUSIONS

Sensory-active volatile FA and FAe are the major contributors to the smell of preterm BM. The associations between lactation stage, maternal characteristics, and volatile compounds, and whether differences in volatile compounds may affect feeding behavior or metabolism, requires further research.

IMPACT

Sensory-active volatile FAs are major contributors to the smell of preterm BM and are influenced by the lactation stage and maternal characteristics. Longitudinal analysis of volatile compounds in preterm BM found that FAs increased with advancing lactation. Colostrum had a higher concentration of medium-chain FAs compared to transitional BM and the concentration of these is associated with socioeconomic status, gestational diabetes, and ethnicity.

Chrononutrition and Breast Milk: A Review of the Circadian Variation of Hormones Present in Human Milk

Introduction

Breast milk contains a wide range of hormones, nutrients, and bioactive compounds. Chrononutrition looks at the interaction between food, both meal timing and meal composition, and circadian rhythms.

Method

This review is a continuation on series on chrononutrition and breast milk. All human studies published in English were included regardless of location or year of publication.

Results

This review identifies the hormonal circadian variation researched in breast milk to date for melatonin, cortisol, cortisone, leptin, and insulin.

Conclusion

The circadian variation observed in some hormones reinforces the superiority of breast milk over formula milk. Melatonin has been the most studied, but more research for all the hormones is needed due to various gaps in the literature and varying levels of study quality. There is insufficient evidence to make recommendations specifically targeting the lactating mother, but we identify and recommend several ideas for future research.

Breastfeeding and risk of overweight in childhood and beyond: a systematic review with emphasis on sibling-pair and intervention studies

BACKGROUND

Breastfeeding is associated with a lower risk of subsequent overweight or obesity, but it is uncertain whether this is a causal relation because most studies have not adequately reduced risk of bias due to confounding.

OBJECTIVES

The aim of this review was to examine whether 1) ever compared with never consuming human milk and 2) different durations of human milk consumption among infants fed human milk are related to later risk of overweight or obesity, with emphasis on sibling-pair and intervention studies.

METHODS

The 2020 Dietary Guidelines Advisory Committee, together with the Nutrition Evidence Systematic Review team, conducted a systematic review of articles relevant to healthy full-term infants in countries with a high or very high level of human development. We searched PubMed, Embase, Cochrane, and CINAHL; dual-screened the results using predetermined criteria; extracted data from and assessed the risk of bias for each included study; qualitatively synthesized the evidence; developed conclusion statements; and graded the strength of the evidence.

RESULTS

The review included 42 articles, including 6 cohorts with sibling-pair analyses and 1 randomized controlled trial of a breastfeeding promotion intervention. Moderate evidence suggested that ever, compared with never, consuming human milk is associated with a lower risk of overweight and obesity at ages 2 y and older, particularly if the duration of human milk consumption is >6 mo. However, residual confounding cannot be ruled out. Evidence was insufficient to determine the relation between the duration of any human milk consumption, among infants fed human milk, and overweight and/or obesity at age 2 y and older.

CONCLUSIONS

Further research, using strong study designs, is needed to disentangle the complex relation between infant feeding practices and the risk of subsequent overweight or obesity, as well as the biological and behavioral mechanisms if the relation is causal.

Human Milk Endocannabinoid Levels as a Function of Obesity and Diurnal Rhythm

The endocannabinoid system is involved in the regulation of a variety of physiological and cognitive processes. While the endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide (N-arachidonoylethanolamine, AEA) have been found in breast milk, their role(s) have yet to be determined. This study determined the normal concentration ranges of endocannabinoids (2-AG and AEA) in breast milk and the influences, if any, of obesity and diurnal rhythms on their levels. Milk samples were collected from 36 breastfeeding mothers at 4–8 weeks postpartum at each feed over a 24-h period, and further stratified into three groups based on body mass index (BMI). The samples were analyzed using liquid chromatography mass spectrometry. AEA was below the limit of detection and 2-AG levels averaged 59.3 ± 18.3 ng/mL (± SD) in women with normal BMI. Wide-ranging 2-AG concentrations in the overweight (65.5 ± 41.9 ng/mL) /obese (66.1 ± 40.6 ng/mL) groups suggest BMI may be a contributing factor influencing its levels. Following a diurnal pattern, there was a significantly higher 2-AG concentration observed during the day, as compared to night time samples. In conclusion, our study clearly suggests that appropriate milk collection and storage conditions are critical. Further, body weight and diurnal rhythm appear to influence levels of 2-AG. Based on these results, future studies are underway to determine what specific roles endocannabinoids may play in human milk and how elevated levels of 2-AG may modulate infant appetite and health.

Melatonin in Early Nutrition: Long-Term Effects on Cardiovascular System

Breastfeeding protects against adverse cardiovascular outcomes in the long term. Melatonin is an active molecule that is present in the breast milk produced at night beginning in the first stages of lactation. This indoleamine appears to be a relevant contributor to the benefits of breast milk because it can affect infant health in several ways. The melatonin concentration in breast milk varies in a circadian pattern, making breast milk a chrononutrient. The consumption of melatonin can induce the first circadian stimulation in the infant's body at an age when his/her own circadian machinery is not functioning yet. This molecule is also a powerful antioxidant with the ability to act on infant cells directly as a scavenger and indirectly by lowering oxidant molecule production and enhancing the antioxidant capacity of the body. Melatonin also participates in regulating inflammation. Furthermore, melatonin can participate in shaping the gut microbiota composition, richness, and variation over time, also modulating which molecules are absorbed by the host. In all these ways, melatonin from breast milk influences weight gain in infants, limiting the development of obesity and comorbidities in the long term, and it can help shape the ideal cellular environment for the development of the infant's cardiovascular system.

Chrononutrition and Breast Milk: A Review of Circadian Variation in Breast Milk Nutrient Composition

Objective

The objective of this literature review was to identify and summarize the current knowledge on the circadian variation of breast milk nutrients and the implications of these findings.

Method

A review of literature was conducted, including all relevant studies regardless of location and year of publication.

Results

The amino acids tyrosine, histidine, aspartic acid and phenylalanine and energy were observed to be higher during the day. Fat and the vitamins B-1, B-2, B-3, B-6, and B-12 were higher at night. Other studies have shown conflicting results or no circadian variation for certain nutrients. Poor reproducibility and small sample sizes affect the quality of existing research.

Conclusion

More research is needed, and longitudinal studies would help assess the effect of breast milk chrononutrition on the long-term health outcomes of infants.

Perspective: Nutritional Status as a Biological Variable (NABV): Integrating Nutrition Science into Basic and Clinical Research and Care

The field of nutrition has evolved from one focused primarily on discovery of the identities, metabolic functions, and requirements for essential nutrients to one focused on the application of that knowledge to the development and implementation of dietary recommendations to promote health and prevent disease. This evolution has produced a deeper appreciation of not only the roles of nutrients, but also factors affecting their functions in increasingly complex global health contexts. The intersection of nutrition with an increasingly more complex global health context necessitates a view of nutritional status as a biological variable (NABV), the study of which includes an appreciation that nutritional status is: 1) not limited to dietary exposure; 2) intimately and inextricably involved in all aspects of human health promotion, disease prevention, and treatment; and 3) both an input and an outcome of health and disease. This expanded view of nutrition will inform future research by facilitating considerations of the contexts and variability associated with the many interacting factors affecting and affected by nutritional status. It will also demand new tools to study multifactorial relations to the end of increasing precision and the development of evidence-based, safe, and effective standards of health care, dietary interventions, and public health programs.

Evaluation of Appetite-Regulating Hormones ın Young Children with Autism Spectrum Disorder

This study aimed to investigate the role of leptin, ghrelin, neuropeptide Y, and nesfatin-1 in young children with autism spectrum disorder (ASD). A total of 44 children with ASD and 44 healthy controls aged 18-60 months were included. Plasma levels of hormones were measured using commercial enzyme-linked immunosorbent assay kits. Plasma leptin and ghrelin levels were significantly higher in the ASD group than in the control group. However, no significant difference for plasma neuropeptide Y and nesfatin-1 levels was detected between the groups. No relation was found between the severity of ASD symptoms, severity of eating problems, and plasma levels of hormones. Leptin and ghrelin may play a potential role in the pathogenesis of ASD.

Sleep Consolidation, Sleep Problems, and Co-Sleeping: Rethinking Normal Infant Sleep as Species-Typical

Infants evolved in the context of close contact (including co-sleeping). Evolutionary context is rarely considered in psychological infant sleep research, and Western sleep researchers make assumptions about what optimal "normal" infant sleep is and how to achieve early, deep, infant sleep consolidation and avoid infant sleep problems. However, an evolutionary and anthropological view of infant sleep as species-typical recognizes that human evolution likely prepared the infant brain for optimal development within its evolutionary context - co-sleeping. Thus, "normal" infant sleep, sleep consolidation, and sleep problems should all be understood within the framework of co-sleeping infants, not the historically new-phenomenon of solitary-sleeping infants. Much work needs to be done in order to understand "normal" infant sleep as species-typical and how adaptive infants are to environments that stray from their evolutionary norm.

Best Practices for Human Milk Collection for COVID-19 Research

In addition to providing life-giving nutrients and other substances to the breastfed infant, human milk can also represent a vehicle of pathogen transfer. As such, when an infectious disease outbreak, epidemic, or pandemic occurs-particularly when it is associated with a novel pathogen-the question will naturally arise as to whether the pathogen can be transmitted through breastfeeding. Until high-quality data are generated to answer this question, abandonment of breastfeeding due to uncertainty can result. The COVID-19 pandemic, which was in full swing at the time this document was written, is an excellent example of this scenario. During these times of uncertainty, it is critical for investigators conducting research to assess the possible transmission of pathogens through milk, whether by transfer through the mammary gland or contamination from respiratory droplets, skin, breast pumps, and milk containers, and/or close contact between mother and infant. To promote the most rigorous science, it is critical to outline optimal methods for milk collection, handling, storage, and analysis in these situations, and investigators should openly share their methods in published materials. Otherwise, the risks of inconsistent test results from preanalytical and analytical variation, false positives, and false negatives are unacceptably high and the ability to provide public health guidance poor. In this study, we provide "best practices" for collecting human milk samples for COVID-19 research with the intention that this will also be a useful guide for future pandemics.

Human neonates prefer colostrum to mature milk: Evidence for an olfactory bias toward the "initial milk"?

OBJECTIVES

Colostrum is the initial milk secretion which ingestion by neonates warrants their adaptive start in life. Colostrum is accordingly expected to be attractive to newborns. The present study aims to assess whether colostrum is olfactorily attractive for 2-day-old newborns when presented against mature milk or a control.

METHODS

The head-orientation of waking newborns was videotaped in three experiments pairing the odors of: (a) colostrum (sampled on postpartum day 2, not from own mother) and mature milk (sampled on average on postpartum day 32, not from own mother) (n tested newborns = 15); (b) Colostrum and control (water; n = 9); and (c) Mature milk and control (n = 13).

RESULTS

When facing the odors of colostrum and mature milk, the infants turned their nose significantly longer toward former (32.8 vs 17.7% of a 120-s test). When exposed to colostrum against the control, they responded in favor of colostrum (32.9 vs 16.6%). Finally, when the odor of mature milk was presented against the control, their response appeared undifferentiated (26.7 vs 28.6%).

CONCLUSIONS

These results indicate that human newborns can olfactorily differentiate conspecific lacteal fluids sampled at different lactation stages. They prefer the odor of the mammary secretion - colostrum - collected at the lactation stage that best matches the postpartum age of their own mother. These results are discussed in the context of the earliest mother-infant chemo-communication. Coinciding maternal emission and offspring reception of chemosignals conveyed in colostrum may be part of the sensory precursors of attunement between mothers and infants.

Melatonin Content of Human Milk: The Effect of Mode of Delivery

Objective: Cesarean section rates are increasing in developed countries and could be performed as an emergency or elective procedure. Our research aim was to determine whether elective cesarean section influences the melatonin content, the main circadian hormone, in human milk. Methods: Twenty-one women after vaginal delivery and 18 women after elective cesarean section were included. Only healthy mothers with normal newborns exclusively breastfed were recruited. Two samples of human milk were collected for each woman at three stages of lactation: colostrum, transitional milk, and mature milk; at each stage, one daytime sample and another nighttime sample were obtained. In total, 228 milk samples were studied. The melatonin content was analyzed by enzyme-linked immunosorbent assay. Results: Melatonin rhythmicity with higher melatonin content at night was maintained at each of the three stages of lactation, regardless of the type of delivery. A higher melatonin content was found in daytime colostrum after cesarean section with respect to colostrum obtained from mothers after vaginal delivery (30.3 pg/mL versus 14.7 pg/mL, p = 0.020). Melatonin content decreased progressively throughout the course of lactation in both groups. This decrease was significant when comparing transitional milk to colostrum in the cesarean group, both in the daytime (p = 0.016) and nighttime samples (p = 0.048). Conclusions: Cesarean section is associated with an increase in daytime colostrum melatonin. No difference was observed in mature milk with respect to vaginal delivery. Melatonin values in human milk decrease during the first month of lactation and circadian rhythmicity was observed irrespective of the mode of delivery.

Circadian Variation in Human Milk Composition, a Systematic Review

Background: Breastfeeding is considered the most optimal mode of feeding for neonates and mothers. Human milk changes over the course of lactation in order to perfectly suit the infant’s nutritional and immunological needs. Its composition also varies throughout the day. Circadian fluctuations in some bioactive components are suggested to transfer chronobiological information from mother to child to assist the development of the biological clock. This review aims to give a complete overview of studies examining human milk components found to exhibit circadian variation in their concentration. Methods: We included studies assessing the concentration of a specific human milk component more than once in 24 h. Study characteristics, including gestational age, lactational stage, sampling strategy, analytical method, and outcome were extracted. Methodological quality was graded using a modified Newcastle-Ottawa Scale (NOS). Results: A total of 83 reports assessing the circadian variation in the concentration of 71 human milk components were included. Heterogeneity among studies was high. The methodological quality varied widely. Significant circadian variation is found in tryptophan, fats, triacylglycerol, cholesterol, iron, melatonin, cortisol, and cortisone. This may play a role in the child’s growth and development in terms of the biological clock.

Human milk fungi: environmental determinants and inter-kingdom associations with milk bacteria in the CHILD Cohort Study

Background

Fungi constitute an important yet frequently neglected component of the human microbiota with a possible role in health and disease. Fungi and bacteria colonise the infant gastrointestinal tract in parallel, yet most infant microbiome studies have ignored fungi. Milk is a source of diverse and viable bacteria, but few studies have assessed the diversity of fungi in human milk.

Results

Here we profiled mycobiota in milk from 271 mothers in the CHILD birth cohort and detected fungi in 58 (21.4%). Samples containing detectable fungi were dominated by Candida, Alternaria, and Rhodotorula, and had lower concentrations of two human milk oligosaccharides (disialyllacto-N-tetraose and lacto-N-hexaose). The presence of milk fungi was associated with multiple outdoor environmental features (city, population density, and season), maternal atopy, and early-life antibiotic exposure. In addition, despite a strong positive correlation between bacterial and fungal richness, there was a co-exclusion pattern between the most abundant fungus (Candida) and most of the core bacterial genera.

Conclusion

We profiled human milk mycobiota in a well-characterised cohort of mother-infant dyads and provide evidence of possible host-environment interactions in fungal inoculation. Further research is required to establish the role of breastfeeding in delivering fungi to the developing infant, and to assess the health impact of the milk microbiota in its entirety, including both bacterial and fungal components.

Melatonin Orchestrates Lipid Homeostasis through the Hepatointestinal Circadian Clock and Microbiota during Constant Light Exposure

Misalignment between natural light rhythm and modern life activities induces disruption of the circadian rhythm. It is mainly evident that light at night (LAN) interferes with the human endocrine system and contributes to the increasing rates of obesity and lipid metabolic disease. Maintaining hepatointestinal circadian homeostasis is vital for improving lipid homeostasis. Melatonin is a chronobiotic substance that plays a main role in stabilizing bodily rhythm and has shown beneficial effects in protecting against obesity. Based on the dual effect of circadian rhythm regulation and antiobesity, we tested the effect of melatonin in mice under constant light exposure. Exposure to 24-h constant light (LL) increased weight and insulin resistance compared with those of the control group (12-h light–12-h dark cycle, LD), and simultaneous supplementation in the melatonin group (LLM) ameliorated this phenotype. Constant light exposure disturbed the expression pattern of a series of transcripts, including lipid metabolism, circadian regulation and nuclear receptors in the liver. Melatonin also showed beneficial effects in improving lipid metabolism and circadian rhythm homeostasis. Furthermore, the LL group had increased absorption and digestion of lipids in the intestine as evidenced by the elevated influx of lipids in the duodenum and decrease in the efflux of lipids in the jejunum. More interestingly, melatonin ameliorated the gut microbiota dysbiosis and improved lipid efflux from the intestine. Thus, these findings offer a novel clue regarding the obesity-promoting effect attributed to LAN and suggest a possibility for obesity therapy by melatonin in which melatonin could ameliorate rhythm disorder and intestinal dysbiosis.