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 International Consultation on Longitudinal Cohort Studies

December 16, 2002
Baltimore Marriott Waterfront
Baltimore, MD

This meeting was held in conjunction with the National Children’s Study, which is led by a consortium of federal agency partners: the U.S. Department of Health and Human Services (including the National Institute of Child Health and Human Development [NICHD] and the National Institute of Environmental Health Sciences [NIEHS] , two parts of the National Institutes of Health , and the Centers for Disease Control and Prevention [CDC] ) and the  U.S. Environmental Protection Agency (EPA) .


Adolfo Correa, M.D., Ph.D., M.P.H., CDC, introduced himself and other members of the planning subcommittee for international consultation on longitudinal studies. He reviewed the agenda for the day’s session, which included an overview of the National Children’s Study (Study), presentations on longitudinal studies in different countries, a presentation on the task force for healthy environments for children in the World Health Organization (WHO), and a discussion of next steps for the international consultation group. He then outlined the short-term objectives of the day’s session:

  • Facilitate the exchange of information among all the investigators interested in longitudinal studies in different countries
  • Provide a forum for interaction among international researchers and participants in the Study
  • Facilitate interactions among the researchers present.

Dr. Correa explained the long-term objectives of the workshop:

  • Formalize and sustain communications among investigators of longitudinal studies in different countries
  • Develop an inventory of international projects, pilot studies, instruments, and expertise
  • Consider possibilities for collaboration with longitudinal studies in other countries.

Overview of U.S. National Children’s Study

Peter Scheidt, M.D., M.P.H., NICHD, NIH, DHHS, provided an overview of the Study. He explained that in 1998, the Presidential Task Force on Environmental Health Risks and Safety Risks to Children was established to develop strategies to reduce the risks of environmental exposures to children. Task force members recognized the need for additional information to guide strategy and policy development, and decided that a longitudinal study could best provide answers to the questions of concern.

In 2000, Congress passed the Children’s Health Act (PL 106-310), authorizing the NICHD to conduct a longitudinal study of environmental influences on children’s health and development. Dr. Scheidt said that the Study would be a high-quality, longitudinal, nationwide investigation of children, their families, and their environment. The environment is broadly defined to include physical, chemical, biological, cultural, and psychosocial exposures. The sample is proposed to number approximately 100,000 children, a cohort of sufficient size to study the common range of exposures and outcomes.

Dr. Scheidt said that in addition to the Study’s focus on very specific, narrowly defined hypotheses, the Study would investigate interactions among various exposures, and the mechanisms by which associations are observed. Measures of exposures will include environmental samples of air, water, and dust; biomarkers for chemicals, infections, and other exposures in blood, breast milk, hair, and tissues; interview data and history about health conditions; serology and medical data; housing and living characteristics; family and social experiences; and neighborhood and community characteristics. Outcome measures will include fetal growth and outcome of pregnancy; birth defects and newborn exam; growth, nutrition, and physical development; medical condition and history; cognitive and emotional development; and mental, developmental, and behavioral conditions.

Dr. Scheidt reviewed the projected timeline of tasks for the Study, noting that selection of the initial centers will begin by late 2004 and enrollment of subjects will begin by mid 2005. The current plan is for the Study to continue at least until 2030. He anticipated first results of outcomes of pregnancy by 2007 to 2008, with subsequent waves of publications thereafter.

Research Presentations

  • Bernardo Horta, Ph.D., Universidade Catolica de Pelotas, Brazil, described his 1982 study of children born to mothers living in the city of Pelotas in southern Brazil. The main objectives of the study were to:
    • Describe the long-term effects of low birth weight, prematurity, and type of delivery
    • Investigate the effect of socioeconomic, environmental, and nutritional factors on growth, development, mortality, and morbidity.

Families were contacted at the time of delivery and then were visited at home. Problems developed when follow-up visits were attempted in 1984. Study researchers managed to overcome this challenge by conducting a door-to-door census of all the houses in the city. Another method of follow-up of the cohort involved conducting interviews and medical tests of males when they appeared for army enlistment. Mortality was monitored by making regular visits to all hospitals, registries, coroner services, and cemeteries in the city.

Another study was begun in 1993 to compare prenatal indicators with those of the 1982 cohort. In this study, researchers used a different strategy to obtain the family’s location information. They requested the mother’s home address, home and work telephone numbers for mother and father, addresses for a relative or close friend, and detailed directions to the mother’s home. They were much more successful with this strategy, finding 94 percent of the cohort at the 12-month follow-up visit.

  • Pedro Oyala, National Commission for the Environment, Chile, described an air quality study that his research group is conducting in Santiago, one of the most polluted cities in the world. The study sample size is 11,000, of which 4,000 are children aged 8 to 12 years. Since 1997, the study has examined the concentrations of different pollutants in indoor, outdoor, and personal environments. Sampling of air quality is conducted at schools in areas of Santiago with low, medium, and high concentrations of air pollution. The pollutants studied include naturally occurring dust particles, ozone, heavy metals, and gases such as nitrous oxide and sulfur dioxide. Family members completed a questionnaire about daily activities, housing, and health.

    Findings of the study revealed that levels of certain pollutants fell by as much as 32 percent from 1997 to 2002. Exposure data show that indoor pollution is much higher than in outdoor environments. Mr. Oyala reported that high levels of indoor pollution are related to the burning of fuels, such as kerosene, and this finding cuts across socioeconomic levels.

  • Per Magnus, M.D., Norwegian Institute of Public Health, Norway, described the planning and development of a study that will recruit 100,000 pregnant women when they arrange for a routine ultrasound scan at 17 weeks gestation. Researchers will obtain biological samples and ask the parents to fill out questionnaires at several points during and after the pregnancy.

    Dr. Magnus explained that many factors (even the cover of the recruitment brochure) affected the response of potential participants. He emphasized the need to be flexible and to make changes as needed. For example, the researchers found errors in the questionnaires, even though they had been pilot tested. In addition, study researchers had not initially planned to include the fathers in the study, but later found it important to do so. He also mentioned the value of maintaining good relationships with the government and the media.

  • Li Zhu, M.D., M.P.H., Peking University Health Science Center, China, discussed a longitudinal cohort study that is part of an international collaborative project with the CDC. This ongoing project is being conducted in areas around the cities of Beijing and Shanghai. When it began in 1991, the study was originally intended to test the hypothesis that a 400 mcg folic acid supplement taken during the first trimester of pregnancy could reduce neural tube defects in newborns. All women in three provinces who were planning to wed (N=247,831) were recruited for the study. They were closely monitored for signs of pregnancy, at which time they were enrolled in the health program providing prenatal care, hospital delivery, and 6 weeks of postpartum visits. Each newborn baby was examined for birth defects, and monitoring continued up to age 7.

    Much of the time and effort expended for the project was spent in training the health workers who saw the patients. A total of 16,000 workers with different functions and responsibilities were trained at the state, district, county, township, and village levels. A large-scale education effort was made to alert all area communities about the project, especially all government officials, health workers, community leaders, parents, and young couples.

  • Thea de Wet, Ph.D., RAU University, South Africa, described a study of 3,275 children born in the greater metropolitan Soweto-Johannesburg area during a 7-week period in late spring 1990. The key aims of the study were to understand the growth, nutrition, health, and development of individuals growing up in an urban environment. Dr. de Wet explained that this study originally intended to study the cohort for one decade, but it was recently extended from birth to age 20.

    A diverse sample from all social groups was included. Researchers collected information on living conditions, family life, daily stresses, common illnesses, injuries, developmental milestones, language use and development, weight, blood pressure, blood lipids, blood lead levels, and indoor and outdoor pollution levels. Dr. de Wet noted that a key to the success of the study was the group of highly skilled research assistants, many of whom had been with the study since its inception.

  • Jorn Olsen, M.D., Ph.D., Danish Epidemiology Science Center, Denmark, described a longitudinal study that was originally planned as part of a large cohort study of all of the Nordic countries (N=400,000). However, only Norway and Denmark started the study.

    From 1996 to September 2002, 100,000 pregnant women were recruited into the cohort in Denmark. Recruitment of study participants was achieved through general practitioners (GPs), who are the gatekeepers of the free public health care system. The GPs referred pregnant women to midwives or specialists, provided materials informing women about the study, obtained informed consent, and took blood samples.

    Measures of exposures are collected only during the intrauterine period and early childhood. These data are linked to the national population registries and other registries that provide endpoint data on health conditions and hospitalizations. Study participants also filled out a brief questionnaire regarding their use of medicine and vitamins before conception and early in the pregnancy. Researchers also collected information on the impact of exposures on fetal growth, infections, dietary factors, and lifestyle/environment.

    Dr. Olsen expressed his opinion that an important part of the research was the need to put data into the computer immediately upon receipt. He explained that whenever they had problems with daily routines, they had severe problems with compliance of the participants in the study. Another key to the system is to have a logistics database to manage all the paperwork.

    Brief Presentations

  • Mark Raizenne, Sc.D., Health Canada, reported that Canada does not have a national plan for a cohort study, but several research groups are currently conducting small sample studies, many of which focus on asthma. Dr. Raizenne described two research approaches currently available in Canada, one related to a system for data collection as part of health care delivery, and another involving several large health surveys that are being conducted mainly for demographic purposes. Attempts are being made to include collection of information on exposure histories and to enable data linkages. He also mentioned that a group of researchers may be soon undertaking a study of a Canadian birth cohort of approximately 10,000 children focusing on gene-environment interactions and susceptible time periods.

    Tye Arbuckle, Ph.D., Health Canada, reported that consultations with scientists in the federal and academic arenas are taking place across the country. Various constituents and nongovernmental agencies interested in children’s environmental health attended a workshop in March 2002. A presentation about the Study was made at the workshop, resulting in widespread support for Canadian-U.S. collaboration.

  • Chanpen Choprapawon, M.D., M.P.H., Ministry of Public Health, Thailand, reported on the study she is directing, entitled "The Prospective Cohort Study of Thai Children." Women in the 28th week of pregnancy were enrolled at five sites in different parts of the country to ensure a diverse sample (N=4,200). The study will follow the children before birth, at birth, and then will interview the mother at home at 1 month, 3 months, 6 months, and 1 year after birth. Researchers conduct follow-up every 6 months after that. Data will be collected about each family’s lifestyle and nutrition, using 3-day and 7-day diary self-report records. Study researchers also will investigate the children’s biomedical, emotional, mental, and moral development. The overall plan for the project is to follow the cohort for 24 years and to include a capacities training and empowerment program for researchers in the country. The study is estimated to cost $2-$2.5 million per year.
  • Hiroshi Hattori described his study, entitled "Better Broadcasting for Children Project." This research will examine the effect of television viewing and video game playing on children’s development. A preliminary survey assessed the validity of survey questions and investigated use of the hypothesis for the main survey. Caregivers will use daily logbooks to record children’s exposure to media. The study also plans to interview children aged 4 to 6 years, and test children when they get to the fifth grade. Other information to be gathered includes demographic data about the main caregiver; physical characteristics of the child; measures of the parent-child relationship; mental health of the caregiver; family functioning; family atmosphere; and the child’s temperament, character, and behavior. The main study (N=1,400 children) will be launched in January of next year, and the cohort will be followed for 12 years.
  • Michael Feehan, Ph.D., Marketing and Planning Systems, New Zealand, discussed the Pacific Islands Families Study (PIF). One critical factor was the fostering of intense community involvement by holding numerous community meetings and actively seeking contact with community and church leaders. Another factor was having a commitment from end users of the research. Other important elements involved proper observance of cultural traditions of Pacific Islanders, such as giving of gifts or small tokens of appreciation, some of which were obtained from corporate sponsors. In addition, by providing referrals and access to health care or social services to study participants, the study has become regarded as a general resource for people to use, which aids in maintaining active participation in the study.
  • Jose Iscovich, M.D., M.Sc., Selikoff Center for Environmental Health and Human Development, Israel, reported on the decision-making process for starting a study of newborns to investigate the effects of sun protection behavior on skin disorders. He described the strategic and logistical aspects of the study structure, noting the need for quality control when storing biological samples, as well as in the linkages of data. The research project is now building the birth cohort and establishing a database with linkages to national registries. Dr. Iscovich also emphasized the importance of different groups from the community, academia, and the private sector working together.
  • Leslie Davidson, M.D., M.Sc., England, and Heather Joshi, Centre for Longitudinal Studies Institute of Education, University of London, England, spoke about the Millennium Cohort Study, involving approximately 18,000 children in four countries (England, Wales, Scotland, and Northern Ireland). The study is weighted for smaller countries, poverty, and non-English speaking participants, which researchers cautioned presented unique challenges. The relatively small sample size limits the kinds of questions asked to more prevalent health conditions, such as asthma, obesity, and injury.
  • Manolis Kogevinas, M.D., Ph.D., National Cancer Institute, NIH and European Cohort Study, Spain, reported that a number of centers in Spain have done research in the areas mentioned by others, such as asthma, infections, neurodevelopment, and the effect of nutrition and antioxidants during pregnancy. These studies have been small, with sample sizes of only hundreds or thousands. However, Dr. Kogevinas is now attempting to work with research groups in 12 European countries that have been doing similar small studies and is considering requesting funding from the European Union (EU) for a large, multipurpose cohort across several countries in the EU. Whether the initiative will proceed is expected to be determined within the next 6 months.
  • Anja Kroke, Ph.D., M.P.H., Research Institute of Child Health, Germany, reported on a cohort study of approximately 700 children. Since 1985, investigators have been studying physiological changes during early childhood and adolescence, not disease outcomes. The study involves collecting detailed information, including weighed food records, 24-hour urine samples, and extensive anthropometric measurements of the children. This has resulted in the accumulation of extensive information and experience in the intense tracking of nutrition, body composition, and growth in children.
  • Leonora Rojas, D.Sc., Ministry of Health, Mexico, reported that, like other countries, Mexico does not yet have a national cohort plan, but is interested in developing one. They have a few studies in process, mainly focusing on air pollution in Mexico City. One ongoing study involves a cohort of 2,000 children followed since 1996, primarily using questionnaires. The Ministry of Health is planning to start telephone interviews, possibly beginning next year, which may become a pilot study for a future cohort. The Ministry of Health is providing support to look at the effects of chemical exposures, interactions with nutrition and SES, and infectious diseases. One practical consideration is the need for political support, as well as financial resources, to start the large cohort study.

WHO Task Force on Healthy Environments for Children

Jenny Pronczuk, M.D., World Health Organization, Switzerland, said that children’s environmental health is a relatively new area of focus for the WHO. For many years, WHO has had a program for the protection of the human environment and a program on child and adolescent health, but only in the last three years have these efforts been combined.

Dr. Pronczuk explained that many advances have been made in the past decade in expansion of access to water and sanitation, rehydration therapies, integrated management of childhood illness, as well as successful campaigns to provide vaccinations and antibiotics. However, there has been a decrease of only 2 million in the childhood death rate (from 12.7 million deaths/year of children under 5 years of age in 1990 to 10.9 million deaths/year in 2000). About 30,000 children still die every day from diseases, of which about half are environmentally related.

Dr. Pronczuk described the major risks and causes of death in children. Where there have been advances, the rate of advancement has not kept up with the population growth rate, so the net result is more children suffering or dying. In an effort to combat these problems, the WHO Task Force on Children’s Environmental Health was established in 1999 to connect researchers who were working in areas related to children’s health and the environment. The August 2000 announcement of the Healthy Environments for Children Initiative led to the formation of the Healthy Environments for Children Alliance in December 2002. Other United Nations organizations, countries, and nongovernmental organizations were invited to join this global alliance. WHO has produced educational materials about the initiative and developed strategies to promote healthy environments.

Next Steps

Dr. Correa led a discussion among the group of assembled researchers about the future of the international consultation. Several participants expressed interest in continuing as a group, remarked on the advantages of ongoing communications, and discussed important considerations for undertaking collaborations. They identified the following action items:

  • The International Interest Group will be formally established under the auspices of Study.
  • Interested participants will look into any other known funding opportunities for these efforts.
  • A Web-based communication system (portal and/or email listserv) will be set up for use by the International Interest Group members.
  • The International Interest Group will identify objectives for its existence and will name chairpersons.
  • Participants will identify other investigators to invite to the International Interest Group.
  • A survey will be developed to collect a summary of all the projects from this meeting, as well as an inventory of Study initiatives.
  • A draft version of the survey will be created and sent to all members for their comments.
  • Information collected will be presented in some form on the Web.
  • Participants should begin making plans for the next meeting.


Catherine Allen, Office of International Environmental Policy, EPA
Tye Arbuckle, Ph.D., Health Canada
Robert Berry, M.D., M.P.H.T.M., CDC, U.S.-China Collaborative Study
Maria Cardoso, Ph.D., University of Sao Paolo, Brazil
Chanpen Choprapawon, M.D., M.P.H., Ministry of Public Health, Thailand
Adolfo Correa, M.D., Ph.D., M.P.H., CDC, DHHS
Leslie Davidson, M.D., M.Sc., Millennium Cohort Study, England
Michael Feehan, Ph.D. Marketing and Planning Systems, New Zealand
Hiroshi Hattori, Japan Broadcasting Corporation, Japan
Bernardo Horta, Ph.D., Universidade Catolica de Pelotas, Brazil
Jose Iscovich, M.D., M.Sc., Selikoff Center for Environmental Health and Human Development, Israel
Heather Joshi, Centre for Longitudinal Studies Institute of Education, University of London, England
Carole Kimmel, Ph.D., Office of Research and Development, EPA
Manolis Kogevinas, M.D., Ph.D., National Cancer Institute, NIH, DHHS, and European Cohort Study, Spain
Anja Kroke, Ph.D., M.P.H., Research Institute of Child Health, Germany
Per Magnus, M.D., Norwegian Institute of Public Health, Norway
Wendy McLaughlin, M.S.W., M.P.A., NICHD, NIH, DHHS
Susan Milburn-Hopwood, Health Canada
Wlodzimierz Okrasa, European Science Foundation, France
Jorn Olsen, M.D., Ph.D., Danish Epidemiology Science Center, Denmark
Pedro Oyala, National Commission for the Environment, Chile
Erica Phipps, M.P.H., North American Commission for Environmental Cooperation, Canada
Jenny Pronczuk, M.D., World Health Organization, Switzerland
Mark Raizenne, Sc.D., Health Canada
Leonora Rojas, D.Sc., Ministry of Health, Mexico
Fuko Saal, Japan Broadcasting Corporation, Japan
Peter Scheidt, M.D., M.P.H., NICHD, NIH, DHHS
Thea de Wet, Ph.D., RAU University, South Africa
Li Zhu, M.D., M.P.H., Peking University Health Science Center, China