Regression discontinuity design for the study of health effects of exposures acting early in life

Regression discontinuity design (RDD) is a quasi-experimental approach to study the causal effect of an exposure on later outcomes by exploiting the discontinuity in the exposure probability at an assignment variable cut-off. With the intent of facilitating the use of RDD in the Developmental Origins of Health and Disease (DOHaD) research, we describe the main aspects of the study design and review the studies, assignment variables and exposures that have been investigated to identify short- and long-term health effects of early life exposures. We also provide a brief overview of some of the methodological considerations for the RDD identification using an example of a DOHaD study. An increasing number of studies investigating the effects of early life environmental stressors on health outcomes use RDD, mostly in the context of education, social and welfare policies, healthcare organization and insurance, and clinical management. Age and calendar time are the mostly used assignment variables to study the effects of various early life policies and programs, shock events and guidelines. Maternal and newborn characteristics, such as age, birth weight and gestational age are frequently used assignment variables to study the effects of the type of neonatal care, health insurance, and newborn benefits, while socioeconomic measures have been used to study the effects of social and welfare programs. RDD has advantages, including intuitive interpretation, and transparent and simple graphical representation. It provides valid causal estimates if the assumptions, relatively weak compared to other non-experimental study designs, are met. Its use to study health effects of exposures acting early in life has been limited to studies based on registries and administrative databases, while birth cohort data has not been exploited so far using this design. Local causal effect around the cut-off, difficulty in reaching high statistical power compared to other study designs, and the rarity of settings outside of policy and program evaluations hamper the widespread use of RDD in the DOHaD research. Still, the assignment variables' cut-offs for exposures applied in previous studies can be used, if appropriate, in other settings and with additional outcomes to address different research questions.

Understanding the Pathways from Prenatal and Post-Birth PM2.5 Exposure to Infant Death: An Observational Analysis Using US Vital Records (2011-2013)

We studied the relationship of prenatal and post-birth exposure to particulate matter < 2.5 μm in diameter (PM_2.5) with infant mortality for all births between 2011 and 2013 in the conterminous United States. Prenatal exposure was defined separately for each trimester, post-birth exposure was defined in the 12 months following the prenatal period, and infant mortality was defined as death in the first year of life. For the analysis, we merged over 10 million cohort-linked live birth-infant death records with daily, county-level PM_2.5 concentration data and then fit a Structural Equation Model controlling for several individual- and county-level confounders. We estimated direct paths from the two exposures to infant death as well as indirect paths from the prenatal exposure to the outcome through preterm birth and low birth weight. Prenatal PM_2.5 exposure was positively associated with infant death across all trimesters, although the relationship was strongest in the third trimester. The direct pathway from the prenatal exposure to the outcome accounted for most of this association. Estimates for the post-birth PM_2.5-infant death relationship were less precise. The results from our study add to a growing literature that provides evidence in favor of the potential harmful effects on human health of low levels of air pollution.

Associations of Feeding Practices in Early Life and Dietary Intake at School Age with Obesity in 10- to 12-Year-Old Arab Children

Understanding the role in pediatric obesity of early life feeding practices and dietary intake at school age is essential for early prevention. The study aimed to examine associations of early life feeding practices, environmental and health-related exposures, and dietary intake at school age as determinants of obesity in children aged 10–12 years. In an earlier study of 233 healthy infants in two Arab towns in northern Israel, neonatal history, feeding practices, and health information were obtained up to age 18 months. This follow-up study assessed dietary intake and anthropometric measurements at age 10–12 years using the 24 h recall method. Overall, 174 children participated in this study. Almost all (98%) the children were breastfed. The prevalence of obesity at school age was 42%. A multivariable model adjusted for energy intake and socioeconomic status showed positive associations of total fat intake and of weight-for-height z score, but not feeding practices in infancy, with obesity. Higher gestational age at birth was associated with lower odds of obesity at age 10–12 years. In conclusion, in a population with near universal breastfeeding, gestational age at birth, weight indicators but not feeding practices in infancy, and total fat intake at school age were associated with increased likelihood of obesity.

The Impact of Prenatal Exposure to Bisphenol A on Male Reproductive Function

Bisphenol A (BPA) is a recognized xenoestrogen, in that it possesses oestrogenic and anti-androgenic properties. These endocrine-disrupting effects of BPA at the estrogen receptor (ER) occur despite the very low affinity of BPA for the ERβ, which is 10,000 times lower than that of 17-β estradiol, and despite the European regulatory authorities stating that BPA is safe, at usual exposure concentrations, the use of BPA in baby drink bottles was banned in 2011. There exists conflicting evidence from human epidemiological studies as to its influence on adult male reproductive function, although animal data is more convincing. This mini-review will report on the limited epidemiological data from human studies relating early life exposure to BPA on adult male reproductive function. A long term follow-up study from Western Australia using a birth cohort, the Raine Study, demonstrated no adverse associations of antenatal exposure to BPA, and potentially a positive association with antenatal BPA exposure with sperm concentration and motility at 20 years of age, although recent scientific reports suggest traditional measures of BPA exposure may underestimate exposure levels, which makes data interpretation potentially flawed.

Early Life Risk Factors in Pediatric EoE: Could We Prevent This Modern Disease?

Eosinophilic esophagitis (EoE) is a chronic antigen-mediated inflammatory disease that affects the esophagus. In the last 20 years, a large number of epidemiological studies showed a significant increase in the incidence and prevalence of EoE, especially in developed countries. This phenomenon might correlate to the overall increase in pediatric allergic diseases or might be a result of improved medical awareness and knowledge through modern diagnostic instruments. Since 1993, when EoE was first recognized as a distinct clinical entity, several signs of progress in the pathophysiology of EoE were achieved. However, a few studies reported data on early risk factors for pediatric EoE and how these factors may interfere with genes. Currently, the most defined risk factors for EoE are male sex, Caucasian race, and atopic comorbidities. Other putative risk factors may include alterations in epithelial barrier function and fibrous remodeling, esophageal dysbiosis, variation in the nature and timing of oral antigen exposure, and early prescription of proton pump inhibitors and antibiotics. Notably, the timing and nature of food antigen exposure may be fundamental in inducing or reversing immune tolerance, but no studies are reported. This review summarized the current evidence on the risk factors that might contribute to the increasing development of EoE, focusing on the possible preventive role of early interventions.

Mutaba'ah-Mother and Child Health Study: protocol for a prospective cohort study investigating the maternal and early life determinants of infant, child, adolescent and maternal health in the United Arab Emirates

INTRODUCTION

Early life exposures, particularly environmental and parental lifestyle factors, have a major influence on children's health and development. Due to increasing interest in the early life developmental origins of diseases, many birth cohorts have been established. These studies constitute a repository of data which researchers use over many years to investigate emerging research questions. However, no such databank or cohort study is available in the United Arab Emirates (UAE). This project aims to establish a prospective mother and child cohort study in Al Ain (Abu Dhabi, UAE) to investigate the maternal and early life determinants of infant, child, adolescent and maternal health of the Emirati population.

METHODS AND ANALYSIS

During the period 2017-2021, this study aims to recruit 10 000 pregnancies at approximately 12 weeks of gestation from hospitals and clinics in Al Ain city. For each mother/newborn pair, an initial dataset will be collected including anthropometric, physiological and biochemical measurements, medical interventions, circumstances of pregnancy, delivery details and neonatal and perinatal growth and health using a combination of questionnaires, interviews and medical record extractions. Baseline data will act as the starting point from which the children will be followed up and re-surveyed at intervals throughout their life course until the age of 16 years, to explore how familial, socioeconomic and lifestyle factors interact with genetic and environmental factors to influence health outcomes and achievements later in life.

ETHICS AND DISSEMINATION

Ethical approval has been granted by the United Arab Emirates University Human Research Ethics Committee and the ethical committees of the participating institutions. Results will be widely disseminated via peer-reviewed manuscripts, conference presentations, media outlets and reports to relevant authorities.

Cohort profile: Finnish Health and Early Life Microbiota (HELMi) longitudinal birth cohort

PURPOSE

HELMi (Health and Early Life Microbiota) is a longitudinal, prospective general population birth cohort, set up to identify environmental, lifestyle and genetic factors that modify the intestinal microbiota development in the first years of life and their relation to child health and well-being.

PARTICIPANTS

The HELMi cohort consists of 1055 healthy term infants born in 2016-2018 mainly at the capital region of Finland and their parents. The intestinal microbiota development of the infants is characterised based on nine, strategically selected, faecal samples and connected to extensive online questionnaire-collected metadata at weekly to monthly intervals focusing on the diet, other exposures and family's lifestyle as well as the health and growth of the child. Motor and cognitive developmental screening takes place at 18 months. Infant's DNA sample, mother's breast milk sample and both parent's spot faecal samples have been collected.

FINDINGS TO DATE

The mean age of the mothers was 32.8 (SD 4.1) and fathers/coparents 34.8 (5.3) years at the time of enrolment. Seventeen percentage (n=180) of the infants were born by caesarean section. Just under half (49%) were firstborns; 50.7% were males. At 3 months of age, 86% of the babies were exclusively breastfed and 2% exclusively formula-fed.

FUTURE PLANS

The current follow-up from pregnancy to first 24 months will be completed in March 2020, totalling to over 10 000 biological samples and over 50 000 questionnaire entries. The results are expected to identify environmental and host factors that affect early gut microbiota development and health, and hence give indications of how to prevent or reverse microbiota perturbations in infancy. This prospective cohort will be followed up further to identify how the early microbiota relates to later health outcomes, especially weight gain, infections and allergic and other chronic diseases.

TRIAL REGISTRATION NUMBER

NCT03996304; Pre-results.

Breast-Feeding Protects Children from Adverse Effects of Environmental Tobacco Smoke

In a cross-sectional study on 433 schoolchildren (aged 6⁻9 years) from 9 schools in Austria, we observed associations between housing factors like passive smoking and lung function as well as improved lung function in children who had been breast-fed. The latter findings urged the question of whether the protective effects of breast-feeding act on environmental stressors or if they act independently. Therefore, the effect of passive smoking on lung function was stratified by breast-feeding. The detrimental effects of passive smoking were significant but restricted to the group of 53 children without breast-feeding. Breast-feeding counteracts the effect of environmental stressors on the growing respiratory organs.

Early Life Exposures and Adult Cancer Risk

Very little is known about the influence of early life exposures on adult cancer risk. The purpose of this narrative review was to summarize the epidemiologic evidence relating early life tobacco use, obesity, diet, and physical activity to adult cancer risk; describe relevant theoretical frameworks and methodological strategies for studying early life exposures; and discuss policies and research initiatives focused on early life. Our findings suggest that in utero exposures may indirectly influence cancer risk by modifying biological pathways associated with carcinogenesis; however, more research is needed to firmly establish these associations. Initiation of exposures during childhood and adolescence may impact cancer risk by increasing duration and lifetime exposure to carcinogens and/or by acting during critical developmental periods. To expand the evidence base, we encourage the use of life course frameworks, causal inference methods such as Mendelian randomization, and statistical approaches such as group-based trajectory modeling in future studies. Further, we emphasize the need for objective exposure biomarkers and valid surrogate endpoints to reduce misclassification. With the exception of tobacco use, there is insufficient evidence to support the development of new cancer prevention policies; however, we highlight existing policies that may reduce the burden of these modifiable risk factors in early life.

The Epigenetic Link between Prenatal Adverse Environments and Neurodevelopmental Disorders

Prenatal adverse environments, such as maternal stress, toxicological exposures, and viral infections, can disrupt normal brain development and contribute to neurodevelopmental disorders, including schizophrenia, depression, and autism. Increasing evidence shows that these short- and long-term effects of prenatal exposures on brain structure and function are mediated by epigenetic mechanisms. Animal studies demonstrate that prenatal exposure to stress, toxins, viral mimetics, and drugs induces lasting epigenetic changes in the brain, including genes encoding glucocorticoid receptor (Nr3c1) and brain-derived neurotrophic factor (Bdnf). These epigenetic changes have been linked to changes in brain gene expression, stress reactivity, and behavior, and often times, these effects are shown to be dependent on the gestational window of exposure, sex, and exposure level. Although evidence from human studies is more limited, gestational exposure to environmental risks in humans is associated with epigenetic changes in peripheral tissues, and future studies are required to understand whether we can use peripheral biomarkers to predict neurobehavioral outcomes. An extensive research effort combining well-designed human and animal studies, with comprehensive epigenomic analyses of peripheral and brain tissues over time, will be necessary to improve our understanding of the epigenetic basis of neurodevelopmental disorders.

Developmental programming: variations in early growth and adult disease

Suboptimal conditions in utero are associated with the development of adult-onset diseases in offspring. Uteroplacental insufficiency in rats is a well-established animal model used to mimic and study the effects of developmental insults relevant to countries of abundant nutrient supply. However, wide-ranging outcomes for the offspring are apparent between the different investigators that use this model and also between cohorts generated in our laboratory. We aimed to explore the reasons for variability in rat models of uteroplacental insufficiency between different investigators and also between our own animal cohorts. We suggest differences in growth and disease development reflect uniqueness in susceptibility and highlight the complexity of interactions between genetic potential and environmental exposures. The impact of adverse exposures in utero has been described as having far-reaching effects that extend well beyond the first, directly exposed generation. However, the resulting phenotypes are not consistent between generations. This suggests that programmed effects are established de novo in each generation and challenges the prediction of disease. Characterization of growth and disease in the numerous rat models has led to our understanding of the impact of early life experiences on adult health. In order to drive the development of preventative and/or treatment strategies, future studies should focus on identifying the initial cause(s) of uteroplacental insufficiency, including genetic origins and the influence of poor diets.