A conception-to-death cohort

Prenatal smoke exposure and mammographic density in mid-life

Tobacco smoke has both carcinogenic effects and anti-estrogenic properties and its inconsistent association with breast cancer risk in observational studies may be because of these competing effects across the lifecourse. We conducted a prospective study of prenatal smoke exposure, childhood household smoke exposure, and adult active smoke exposure and mammographic density, a strong intermediate marker of breast cancer risk, in an adult follow-up of existing US birth cohorts. Specifically, we followed up women who were born between 1959 and 1967 and whose mothers participated in either the Collaborative Perinatal Project (Boston and Providence sites) or the Childhood Health and Development Study in California. Of the 1134 women interviewed in adulthood (ranging in age from 39 to 49 years at interview), 79% had a screening mammogram. Cigarette smoking was reported by mothers at the time of their pregnancy; 40% of mothers smoked while pregnant. Women whose mothers smoked during pregnancy had a 3.1% (95% confidence interval (CI) = -6.0%, -0.2%) lower mammographic density than women whose mothers did not smoke during pregnancy. When we further accounted for adult body mass index and adult smoking status, the association remained (β = -2.7, 95% CI = -5.0, -0.3). When we examined patterns of smoking, prenatal smoke exposure without adult smoke exposure was associated with a 5.6% decrease in mammographic density (β = -5.6, 95% CI = -9.6, -1.6). Given the strength of mammographic density as an intermediate marker for breast cancer, the inverse associations between mammographic density and smoking patterns across the lifecourse may help explain the complex association between cigarette smoking and breast cancer risk.

Maternal Prenatal Nutrition and Health in Grandchildren and Subsequent Generations

This review focuses on how maternal prenatal nutritional states may affect the health of grandchildren and later generations. We first summarize the limited current data in human populations relating to the potential transmission of phenotypes across multiple generations that result from the nutritional experience of a pregnant woman. We then discuss findings from other species, especially mammals, that provide important clues as to whether, and if so how, such transmission could occur in humans. Finally, we consider how studies of human populations could be best designed to detect transmission across multiple generations. We argue that just as epidemiologists embraced a life-course perspective to human health and disease in the twentieth century, we must now seek to better understand how health and disease could be shaped across multiple generations.

The Early Determinants of Adult Health Study

This issue of the Journal features collaborative follow-up studies of two unique pregnancy cohorts recruited during 1959-1966 in the United States. Here we introduce the Early Determinants of Adult Health (EDAH) study. EDAH was designed to compare health outcomes in midlife (age 40s) for same-sex siblings discordant on birthweight for gestational age. A sufficient sample of discordant siblings could only be obtained by combining these two cohorts in a single follow-up study. All of the subsequent six papers are either based upon the EDAH sample or are related to it in various ways. For example, three papers report results from studies that significantly extended the 'core' EDAH sample to address specific questions. We first present the overall design of and rationale for the EDAH study. Then we offer a synopsis of past work with the two cohorts to provide a context for both EDAH and the related studies. Next, we describe the recruitment and assessment procedures for the core EDAH sample. This includes the process of sampling and recruitment of potential participants; a comparison of those who were assessed and not assessed based on archived data; the methods used in the adult follow-up assessment; and the characteristics at follow-up of those who were assessed. We provide online supplementary tables with much further detail. Finally, we note further work in progress on EDAH and related studies, and draw attention to the broader implications of this endeavor.

The role of birth cohorts in studies of adult health: the New York women's birth cohort

Epidemiological studies investigating associations between early life factors and adult health are often limited to studying exposures that can be reliably recalled in adulthood or obtained from existing medical records. There are few US studies with detailed data on the pre- and postnatal environment whose study populations are now in adulthood; one exception is the Collaborative Perinatal Project (CPP). We contacted former female participants of the New York site of the CPP who were born from 1959 to 1963 and were prospectively followed for 7 years to examine whether the pre- and postnatal environment is associated with adult health in women 40 years after birth. The New York CPP cohort is particularly diverse; at enrolment, the race/ethnicity distribution of mothers was approximately 30% White, 40% Black and 30% Puerto Rican. Of the 841 eligible women, we successfully traced 375 women (45%) and enrolled 262 women (70% of those traced). Baseline data were available for all eligible women, and we compared those who participated with the remaining cohort (n = 579). Higher family socio-economic status at age 7, availability of maternal social security number, and White race/ethnicity were statistically significantly associated with a higher probability of tracing. Of those traced, race/ethnicity was associated with participation, with Blacks and Puerto Ricans less likely to participate than Whites (OR = 0.5, 95% CI 0.3, 0.8, and OR = 0.5, 95% CI 0.3, 1.0, respectively). In addition, higher weight at 7 years was associated with lower participation (OR = 0.95, 95% CI 0.92, 0.99), but this association was observed only among the non-White participants. None of the other maternal characteristics, infant or early childhood growth measures was associated with participation or with tracing, either overall or within each racial/ethnic subgroup. Daughters' recall of early life factors such as pre-eclampsia (sensitivity = 24%) and birthweight were generally poor, with the latter varying by category of birthweight with the highest sensitivity for the largest babies (81%) and the lowest sensitivity for the smallest babies (54%). These data reinforce the need to rejuvenate existing birth cohorts with prospective data for life course studies of adult health. Understanding the factors that are associated with tracing and participation in these existing cohorts will help in interpreting the validity and generalisability of the findings from these invaluable cohorts.

Prenatal nutritional deficiency and risk of adult schizophrenia

Converging evidence suggests that a neurodevelopmental disruption plays a role in the vulnerability to schizophrenia. The authors review evidence supporting in utero exposure to nutritional deficiency as a determinant of schizophrenia. We first describe studies demonstrating that early gestational exposure to the Dutch Hunger Winter of 1944--1945 and to a severe famine in China are each associated with an increased risk of schizophrenia in offspring. The plausibility of several candidate micronutrients as potential risk factors for schizophrenia and the biological mechanisms that may underlie these associations are then reviewed. These nutrients include folate, essential fatty acids, retinoids, vitamin D, and iron. Following this discussion, we describe the methodology and results of an epidemiologic study based on a large birth cohort that has tested the association between prenatal homocysteine, an indicator of serum folate, and schizophrenia risk. The study capitalized on the use of archived prenatal serum specimens that make it possible to obtain direct, prospective biomarkers of prenatal insults, including levels of various nutrients during pregnancy. Finally, we discuss several strategies for subjecting the prenatal nutritional hypothesis of schizophrenia to further testing. These approaches include direct assessment of additional prenatal nutritional biomarkers in relation to schizophrenia in large birth cohorts, studies of epigenetic effects of prenatal starvation, association studies of genes relevant to folate and other micronutrient deficiencies, and animal models. Given the relatively high prevalence of nutritional deficiencies during pregnancy, this work has the potential to offer substantial benefits for the prevention of schizophrenia in the population.

Environmental determinants of infectious disease: a framework for tracking causal links and guiding public health research

BACKGROUND

Discoveries that emerging and re-emerging pathogens have their origin in environmental change has created an urgent need to understand how these environmental changes impact disease burden. In this article we present a framework that provides a context from which to examine the relationship between environmental changes and disease transmission and a structure from which to unite disparate pieces of information from a variety of disciplines.

METHODS

The framework integrates three interrelated characteristics of environment-disease relationships: a) Environmental change manifests in a complex web of ecologic and social factors that may ultimately impact disease; these factors are represented as those more distally related and those more proximally related to disease. b) Transmission dynamics of infectious pathogens mediate the effects that environmental changes have on disease. c) Disease burden is the outcome of the interplay between environmental change and the transmission cycle of a pathogen.

RESULTS

To put this framework into operation, we present a matrix formulation as a means to define important elements of this system and to summarize what is known and unknown about the these elements and their relationships. The framework explicitly expresses the problem at a systems level that goes beyond the traditional risk factor analysis used in public health, and the matrix provides a means to explicitly express the coupling of different system components.

CONCLUSION

This coupling of environmental and disease transmission processes provides a much-needed construct for furthering our understanding of both specific and general relationships between environmental change and infectious disease.

The National Children's Study: a 21-year prospective study of 100,000 American children

Prospective, multiyear epidemiologic studies have proven to be highly effective in discovering preventable risk factors for chronic disease. Investigations such as the Framingham Heart Study have produced blueprints for disease prevention and saved millions of lives and billions of dollars. To discover preventable environmental risk factors for disease in children, the US Congress directed the National Institute of Child Health and Human Development, through the Children's Health Act of 2000, to conduct the National Children's Study. The National Children's Study is hypothesis-driven and will seek information on environmental risks and individual susceptibility factors for asthma, birth defects, dyslexia, attention-deficit/hyperactivity disorder, autism, schizophrenia, and obesity, as well as for adverse birth outcomes. It will be conducted in a nationally representative, prospective cohort of 100,000 US-born children. Children will be followed from conception to 21 years of age. Environmental exposures (chemical, physical, biological, and psychosocial) will be assessed repeatedly during pregnancy and throughout childhood in children's homes, schools, and communities. Chemical assays will be performed by the Centers for Disease Control and Prevention, and banks of biological and environmental samples will be established for future analyses. Genetic material will be collected on each mother and child and banked to permit study of gene-environment interactions. Recruitment is scheduled to begin in 2007 at 7 Vanguard Sites and will extend to 105 sites across the United States. The National Children's Study will generate multiple satellite studies that explore methodologic issues, etiologic questions, and potential interventions. It will provide training for the next generation of researchers and practitioners in environmental pediatrics and will link to planned and ongoing prospective birth cohort studies in other nations. Data from the National Children's Study will guide development of a comprehensive blueprint for disease prevention in children.

Invited commentary: taking the search for causes of schizophrenia to a different level

In recent years, epidemiologists have established major variations in the incidence of schizophrenia and have begun to investigate the causes of these variations. The report by Pedersen and Mortensen (Am J Epidemiol 2006;163:971-8) in this issue of the Journal examines the contribution of family-level factors to the urban-rural difference in the incidence of schizophrenia. Their results suggest that familial life in urban environments confers some effect that persists after families move to rural settings. Taking these findings together with those of previous studies, it appears that factors operating at the level of the social context, the family, and the individual may all contribute to the urban-rural difference in schizophrenia incidence. This work exemplifies an integrative, multilevel approach to epidemiologic research that employs principles central to eco-epidemiology and other, similar frameworks.

A life course approach to chronic disease epidemiology

A life course approach to chronic disease epidemiology uses a multidisciplinary framework to understand the importance of time and timing in associations between exposures and outcomes at the individual and population levels. Such an approach to chronic diseases is enriched by specification of the particular way that time and timing in relation to physical growth, reproduction, infection, social mobility, and behavioral transitions, etc., influence various adult chronic diseases in different ways, and more ambitiously, by how these temporal processes are interconnected and manifested in population-level disease trends. In this review, we discuss some historical background to life course epidemiology and theoretical models of life course processes, and we review some of the empirical evidence linking life course processes to coronary heart disease, hemorrhagic stroke, type II diabetes, breast cancer, and chronic obstructive pulmonary disease. We also underscore that a life course approach offers a way to conceptualize how underlying socio-environmental determinants of health, experienced at different life course stages, can differentially influence the development of chronic diseases, as mediated through proximal specific biological processes.

Ethics and research assessing the relative roles of genes and the environment

Research on the interaction of genes and the environment is revealing that many human diseases have both genetic and environmental components. Even traditional "environmental" diseases, such as infections, appear to interact with genetic components in the human host. Environmental genetics research will inevitably increase understanding of individual susceptibilities to toxic exposures in the environment and harmful side effects of medications; therefore, it has great promise for improving the prevention and treatment of human diseases. However, realizing the benefits of this research requires careful attention to ethical issues that are particularly relevant in this context. This article reviews some of the most pressing issues related to research design and methods, as well as from the application of research results (e.g., workplace genetic screening and legal toxic torts, personal medical responsibility, and the relationship between genetics and public health measures).