IJE Advance Access originally published online on February 19, 2008
International Journal of Epidemiology 2008 37(4):716-720; doi:10.1093/ije/dyn028
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Cohort Profile: The Institute of Nutrition of Central America and Panama (INCAP) Nutrition Trial Cohort Study
1 Hubert Department of Global Health, Rollins School of Public Health, Emory University, Atlanta GA 30322, USA.
2 Instituto de Nutrición de Centro América y Panamá (INCAP), Guatemala City, Guatemala.
3 International Food Policy Research Institute (IFPRI), Washington DC, USA.
* Corresponding author. Hubert Department of Global Health, Emory University, 1518 Clifton Rd., NE, Atlanta GA 30322, USA. E-mail: rmart77{at}sph.emory.edu
Accepted 22 January 2008
 |
How did the study come about? |
|---|
Top
How did the study...
What does it cover?In the mid-1960s, protein deficiency was seen as the most important nutritional problem facing the poor in the developing countries, and there was considerable concern that this deficiency affected children's ability to learn. The Institute of Nutrition of Central America and Panama (INCAP), based in Guatemala, became the locus of a series of studies on this subject, that informed the development of a large-scale randomized nutritional intervention trial that ran from 1969 to 1977.1,2 The principal hypothesis underlying the intervention was that improved preschool nutrition would accelerate mental development. An examination of the effects on physical growth was also included to verify that the nutritional intervention had biological potency, which was demonstrated.2 Initially, 300 communities were screened to identify villages of appropriate size, compactness, ethnicity and language, diet, access to health care facilities, demographic characteristics, nutritional status and degree of physical isolation. From this group, two pairs of similar villages were identified; then, one village from each pair was chosen randomly to receive a nutritious supplement and the remaining two villages a control drink. All four villages chosen are located relatively close to the Atlantic Highway, connecting Guatemala City to Guatemala's Caribbean coast.
The ‘treatment’ drink was formulated as an ‘Atole’, or a type of hot gruel consumed in Guatemala, and was made from Incaparina, a vegetable protein mixture developed by INCAP, dry skim milk, sugar and flavouring. Atole delivered 11.5 g of high-quality protein and 163 kcal/cup (180 ml). The control drink called ‘Fresco’ was devoid of protein and had only a small amount of sugar and flavouring; it was similar to local drinks and was served at room temperature. Fresco provided 59 kcal/cup. Fear of ‘empty calories’ and a desire to further isolate the contrast in protein between the two drinks led to vitamins, iron and fluoride being added to Fresco to achieve similar concentrations (by volume) as those of Atole.
Procedures in Atole and Fresco villages were similar, including the layouts of the supplementation centres and the measurements of attendance and intake. Each supplement was provided in a supplementation centre twice a day including weekends, in mid-morning and mid-afternoon in order to minimize possible influences on meal patterns at home. Attendance was open to all villagers but was recorded only for pregnant and breastfeeding women and for children 7 years or younger. A pre-filled cup was given to each person but more was given if desired. Intakes were recorded carefully, after subtracting leftovers from the amounts given. Staff operating these centres were rotated across the four study villages.
INCAP also established medical clinics offering preventive and curative services; these were staffed by auxiliary nurses under the supervision of physician. Medical services were free and not tied to participation in the study.
The follow-up studies, conducted since 1988, have been designed to link early childhood growth and development to long-term adult outcomes, to test whether the enhanced nutrition provides long-lasting benefits.
|
What does it cover? |
|---|
The primary focus of the follow-up studies has been the development of human capital in relation to exposure to the nutrition supplementation trial. Areas of interest to date have included (i) growth, strength and flexibility and body composition; (ii) medical history and cardio-metabolic risk factors; (iii) schooling attainment and cognitive functioning; (iv) marriage, reproduction and family formation; (v) occupation, income, asset and wealth accumulation; (vi) mother–child interactions and (vii) diet and physical activity.
|
Who is in the sample? |
|---|
The index individuals in the study population are the men and women who were eligible to have supplement intakes recorded during the original trial. They were either under 7 years of age at the start of the trial in early 1969, or were born during the trial period, through September 1977. A total of 2392 individuals meet this criterion. In addition, supplemental studies have enrolled the spouses, parents and the children of these individuals (see below).
The most comprehensive follow-up of the entire cohort took place in 2002–4. At that time, 1570 individuals completed at least part of the data collection process. Some selected characteristics of this sample are provided in Table 1.
|
|
How often have they been followed up? |
|---|
Follow-up studies of cohort members were conducted in 1988–89, 1996–99, 2002–04 and 2005–07 (Figure 1). Details of the eligible sample for each survey wave are in Table 2. Data on these individuals have been complemented by socio-economic histories of the villages using key informant interviews, focus groups and archival work. In addition, the four study villages participated in a study of newborn birth weights from 1991–96.
|
|
|
What has been measured? |
|---|
The domains of interest have concentrated on growth and development of human capital. Key domains of study in each survey wave are in Table 3.
|
|
What has been found? |
|---|
With over 200 publications from the study database, the project has provided data that have been influential in establishing the role of early life nutrition for growth and cognitive functioning. A full list of all study publications can be found at the study website: www.sph.emory.edu/humancapital. The study's main findings for child growth and development have been summarized in previous reviews.2–4 Recently, we have shown that the timing of child growth is related to the development of adult height, fat mass and fat free mass.5
Most recently, the study has shown that exposure to Atole at ages 0–36 months is associated with increments in both a measure of reading comprehension and in the Ravens’ Progressive matrices6 and with a 46% increase in net wages for individuals exposed to Atole between 0 and 24 months.7 Conversely, given the concerns that enhanced feeding of children might promote obesity and its consequences, it is reassuring that exposure to Atole at 0–24 months, the age period in which growth proportion is enhanced, was not associated with increased levels of cardio-metabolic risk factors.8 These three publications demonstrate that continued long-term effects of nutrition supplementation in childhood on a wide range of measures of human capital can be demonstrated even 30 years after the end of the intervention.
The study is well poised to address questions related to the nutrition transition in Guatemala. All cohort members were born and spent their childhoods in a relatively impoverished rural environment, and are now experiencing increased opportunities for migration, occupation and lifestyle. We have started to document these changes, finding that physical activity is a key factor preventing the development of obesity and its sequelae.9 In addition, the most recent wave of data collection has been designed to assess whether the effects of nutrition supplementation in childhood are reflected in changes in trans-generational resource allocation.
|
What is attrition like? |
|---|
Among the 2392 original cohort members, 274 (11%) were known to have died by 2002 (largely as a result of childhood illnesses); 162 have left Guatemala (primarily for the United States); and no information as available for 101 (4%). Among the 1855 presumed to be alive and living in Guatemala, 1113 lived in the original villages, 155 lived in nearby villages, 419 lived in or near Guatemala City and 168 lived elsewhere in Guatemala. In the 2002–4 wave of data collection, among the 1855, informed consent was obtained and at least partial data collection was conducted with 1570 individuals (752 males and 818 females). This represents a response rate among those alive of 73.8%, if the 101 for whom vital status is not known are presumed to be alive, or 77.8% if they are presumed to be dead. Response rates were somewhat lower for the measurement of blood glucose and lipid levels due to the requirement to obtain fasting samples. A discussion of form-specific response rates and attrition by major category is presented elsewhere.10
|
What are the main strengths and weaknesses? |
|---|
The unique features of the cohort include (i) the community randomized exposure to either Atole or Fresco; (ii) the length of follow-up, with all cohort members now over 30 years old; (iii) the relatively high rates of tracing and contact and (iv) the breadth of contextual data available at individual and community levels, stretching back over 40 years.
The primary weaknesses of the study derive from several characteristics of the original trial. (i) There are only two pairs of villages, and hence there is limited power to test for intervention effects using the village as the unit of observation. While it is possible, however, to use the ages at which cohort members were exposed to the trial as exogenous exposures to increase the number of degrees of freedom for such village-based analyses, there is substantial overlap among such categorizations.8 (ii) Sample size is limited to address questions for which repeated measures throughout early childhood are required. Follow-up in the original trial was censored due to study closeout in 1977 or reaching 7 years of age between 1969 and 1977. (iii) A third limitation is that there are to date no biobank data, although plans are being made to collect such data in the next study wave.
|
Can I get access to the data? Where can I find out more? |
|---|
Requests for access to the 2002–04 follow-up data may be made through the project website (www.sph.emory.edu/humancapital). Currently, it is planned to make the data available from the 2005–07 survey through the same website sometime in 2009. Researchers should be aware that because the study population originates from four readily identifiable villages, there are significant data privacy issues associated with the use of these data. The study group welcomes suggestions for collaborative research (please contact the corresponding author). Funding from external sources may be required.
|
Acknowledgements |
|---|
Funding for the many waves of data collection has been provided by the US National Institutes of Health (NIH), the Nestle Foundation, and the Thrasher Research Foundation. The Human Capital study was funded by NIH grant TW-005598, and the Inter-Generational Transfers Study is funded through NIH grant HD-045627. In recent years, funding for data analysis has been provided by the NIH, the US National Science Foundation, and the American Heart Association. The authors are indebted to the many investigators and support staff who over 40 years have developed and sustained this unique cohort. Finally, the investigators thank the cohort members for their continued cooperation.
Conflict of interest: None declared.
|
References |
|---|
1 Habicht J-P, Martorell R. Objectives, research design, and implementation of the INCAP longitudinal study. Food Nutr Bull (1992) 14:176–90.
2 Martorell R, Habicht J-P, Rivera JA. History and design of the INCAP longitudinal study (1969-77) and its follow-up (1988-89). J Nutr (1995) 125:1027S–41S.
3 Martorell R. Results and implications of the INCAP follow-up study. J Nutr (1995) 125:1127S–38S.
4 Martorell R, Behrman J, Flores R, Stein AD. Rationale for a follow-up focusing on economic productivity. Food Nutr Bull (2005) 26(Suppl. 1):S5–14.[Medline]
5 Corvalán C, Gregory CO, Ramirez-Zea M, Martorell R, Stein AD. Size at birth, infant, early and later childhood growth and adult body composition: a prospective study in a stunted population. Int J Epidemiol (2007) 36:550–57.
6 Stein AD, Wang M, DiGirolamo A, et al. Nutritional supplementation in early childhood, schooling, and intellectual functioning in adulthood: a prospective study in Guatemala. Arch Pediatr Adolesc Med (2008) (In press).
7 Hoddinott J, Maluccio J, Behrman J, Flores R, Martorell R. Effect of a nutrition intervention during early childhood on economic productivity in Guatemalan adults. Lancet (2008) 371:411–16.[CrossRef][Medline]
8 Stein AD, Wang M, Ramirez-Zea M, et al. Exposure to a nutrition supplementation intervention in early childhood and risk factors for cardiovascular disease in adulthood: evidence from Guatemala. Am J Epidemiol (2006) 164:1160–70.
9 Gregory CO, Dai J, Ramirez-Zea M, Stein AD. Occupation is more important than rural-urban residence in explaining prevalence of metabolic and cardiovascular disease risk in Guatemalan adults. J Nutr (2007) 137:1314–19.
10 Grajeda R, Flores R, Stein AD, Maluccio JA, Behrman J, Martorell R. Design and implementation of the INCAP Early Nutrition, Human Capital and Economic Productivity follow-up study, 2002–2004. Food Nutr Bull (2005) 26(Suppl. 1):S15–24.[Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  L. S Adair, R. Martorell, A. D Stein, P. C Hallal, H. S Sachdev, D. Prabhakaran, A. K Wills, S. A Norris, D. L Dahly, N. R Lee, et al. Size at birth, weight gain in infancy and childhood, and adult blood pressure in 5 low- and middle-income-country cohorts: when does weight gain matter? Am. J. Clinical Nutrition, May 1, 2009; 89(5): 1383 - 1392. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. D. Stein, M. Wang, A. DiGirolamo, J. Hoddinott, R. Martorell, M. Ramirez-Zea, and K. Yount Height for Age Increased While Body Mass Index for Age Remained Stable between 1968 and 2007 among Guatemalan Children J. Nutr., February 1, 2009; 139(2): 365 - 369. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||