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Adolescent cohorts assessing growth, cardiovascular and cognitive outcomes in low and middle-income countries

  • Joseph L. Ward ,

    Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Validation, Writing – original draft, Writing – review & editing

    joseph.ward.14@ucl.ac.uk

    Affiliation UCL Institute of Child Health, University College London, London, United Kingdom

  • Katherine Harrison,

    Roles Data curation, Formal analysis, Methodology, Validation, Writing – original draft, Writing – review & editing

    Affiliation University College London Hospitals NHS Foundation Trust, London, United Kingdom

  • Russell M. Viner,

    Roles Conceptualization, Investigation, Methodology, Supervision, Writing – original draft, Writing – review & editing

    Affiliation UCL Institute of Child Health, University College London, London, United Kingdom

  • Anthony Costello,

    Roles Conceptualization, Methodology, Supervision, Writing – review & editing

    Affiliations UCL Institute for Global Health, University College London, London, United Kingdom, Department of Maternal, Newborn, Child and Adolescent Health (MCA) World Health Organization, Geneva, Switzerland

  • Michelle Heys

    Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Supervision, Writing – original draft, Writing – review & editing

    Affiliation UCL Institute for Global Health, University College London, London, United Kingdom

Abstract

Introduction

Life-course studies are needed to explore how exposures during adolescence, particularly puberty, contribute to later cardiovascular risk and cognitive health in low and middle-income countries (LMIC), where 90% of the world’s young people live. The extent of any existing cohorts investigating these outcomes in LMIC has not previously been described.

Methods

We performed a systematic literature review to identify population cohort studies of adolescents in LMIC that assessed anthropometry and any of cardiovascular risk (blood pressure, physical activity, plasma glucose/lipid profile and substance misuse), puberty (age at menarche, Tanner staging, or other form of pubertal staging) or cognitive outcomes. Studies that recruited participants on the basis of a pre-existing condition or involved less than 500 young people were excluded.

Findings

1829 studies were identified, and 24 cohorts fulfilled inclusion criteria based in Asia (10), Africa (6) and South / Central America (8). 14 (58%) of cohorts identified were based in one of four countries; India, Brazil, Vietnam or Ethiopia. Only 2 cohorts included a comprehensive cardiovascular assessment, tanner pubertal staging, and cognitive outcomes.

Conclusion

Improved utilisation of existing datasets and additional cohort studies of adolescents in LMIC that collect contemporaneous measures of growth, cognition, cardiovascular risk and pubertal development are needed to better understand how this period of the life course influences future non-communicable disease morbidity and cognitive outcomes.

Introduction

Almost a quarter of the global population is aged between 10–24 years, 90% of whom live in developing countries[1]. The burden of mortality and morbidity within this population is more significant than previously recognized, and very largely preventable[2]. The health of adolescents and young people are intrinsically linked to those of the next generation, and it is during this stage of the life course where we have the greatest opportunity to influence the future burden of non-communicable disease, and the adoption of risk behaviours which may determine other health outcomes in adulthood. It is during adolescence where unhealthy behaviours associated with cardiovascular disease such as smoking and alcohol use are initiated and established[3], where mental health problems first arise, and where risks associated with pregnancy and birth are greatest. Of the 10 leading causes of disability adjusted life years (DALY) identified in the global burden of disease study, 6 are determined during this period of the life course[4]. There is now growing international recognition of the importance of investing in adolescent health, particularly in low and middle-income countries (LMICs). To do so will bring a triple dividend: benefits now, for future adult health, and for the next generation[5].

Despite this importance to global development, data collection and studies of adolescent health are very limited outside high-income countries. As adolescent health outcomes were largely absent from the Millennium Development Goal agenda, and this period of the life course has been perceived as one of relative health, the importance of collecting data within this age group, particularly within resource poor settings, has previously been overlooked. Young people are often not included in data collection systems that frequently do not disaggregate data by age across the early life course[6]. Further, indicators describing the social contexts in which adolescents live, study and work, known to be powerful determinants of morbidity and mortality in this age group, often do not feature in global data systems. There is an acknowledged need to develop capacity in national statistical systems in LMIC and expand adolescent participation in research to better understand this crucial stage of the life course[6].

Collecting data through life-course studies of exposures during puberty is an essential part of this. Puberty is a time of immense physiological and psychological change where future health and social trajectories are set in motion[7]. The timing of onset of puberty has been shown to influence multiple health outcomes[7], and the interaction between how growth and pubertal changes impact cardiovascular risk and cognitive outcomes differently is of particular interest.

Adult cognitive outcomes, particularly in language, memory and executive function, are heavily linked to exposures during childhood and adolescence[8] and these may be more important than those during the prenatal period or later in adulthood[9]. Pubertal development and growth during adolescence are influential in this; the timing of puberty impacts directly on grey and white matter development[10] and earlier puberty in women may be protective for adulthood cognitive function[8, 11]. However, the benefit to brain development of early puberty may come at the cost of worse cardiovascular outcomes later in life. This could represent an example of the theory within evolutionary biology of “life-history trade-offs,” where an organism sacrifices long-term life expectancy to prioritise short term survival and greater likelihood of reproductive success[12]. Early menarche is associated with increased body mass index (BMI) in adolescence and adulthood, after adjusting for childhood BMI[13] and early puberty has also been associated with increased BMI and blood pressure in males, independent of pre-pubertal weight, birth-weight or social class[14]. A recent systematic review also found early puberty to be associated with cardiovascular mortality, hypertension, metabolic syndrome, abnormal glycaemia and obesity[15]. Certain patterns of growth during adolescence, childhood and infancy are also associated with increased cardiovascular risk[16]. For example, greater sitting height, primarily determined during adolescence, was associated with increased risk of diabetes and dyslipidaemia in one Chinese cohort[17]. Exploring these relationships will require longitudinal studies of adolescence collecting data on these outcomes simultaneously.

Much of the evidence for these associations comes from studies in high–income settings, and extrapolating their findings to LMICs is problematic for many reasons. Firstly, the prevalence of exposures and outcomes pertinent to adolescent health, growth, puberty and future cardiovascular and cognitive outcomes, such as poor nutritional status and tobacco, alcohol and substance use, varies by income group[6]. The nature of exposures may also differ, for example a third of tobacco intake in South Asia is smokeless[18]. Whereas physical activity in LMICs is primarily due to commuting, manual labour, or domestic work, in high-income countries this is related to leisure activities. Further, the confounding structure of exposures and outcomes will vary; the protective role of breastfeeding on childhood adiposity shown in developed countries have not been replicated in non-European settings, suggesting socioeconomic status was confounding this association[19]. Socio-economic inequalities in cardiovascular disease are also dependent on level of economic development[20], with childhood obesity being common amongst low socioeconomic groups in wealthy countries, and in high socioeconomic groups in the developing world[21]. Body composition may also vary for a given body size, and have differing influence on non-communicable risk. For example, low birth weight infants from LMICs may have a “thin-fat” phenotypic body composition that can increase risk of type 2 diabetes[22].

In order to assess the need for further longitudinal studies investigating these outcomes outside high-income countries, we performed a systematic literature review to identify cohort studies of adolescents in LMICs that include assessments of growth, cardiovascular risk, pubertal development and cognition. We hypothesised there would be limited availability of cohort studies assessing these variables in LMICs.

Methods

Search strategy

We performed a systematic literature search on 24th Feb 2016 of MEDLINE. Keywords (MeSH and text words) used to describe the study population were: adolescent, adolescence, young person, teenager, youth and children (see Appendix). Keywords used to identify relevant study design were: birth cohort, panel study, longitudinal study and cohort study. Keywords used to identify studies in relevant settings were: low and middle income country, low income country, middle income country, developing country, and the individual country names for all those defined as low or middle income using the World Bank lending classification of Gross National Income (GNI) per capita of less than $12735 in 2015[23]. Reference lists of selected papers were then searched for any further relevant studies.

Data extraction

We used the online literature review tool www.covidence.org to extract the data. Inclusion criteria are listed in Table 1. An article was eligible if it referred to a longitudinal study design, was set in a LMIC, included participants aged between 10 and 19 years and assessed anthropometry (objectively recorded) and any of cardiovascular risk (any one of: blood pressure, physical inactivity, plasma glucose/lipid profile or substance misuse), puberty (age at menarche, Tanner staging, or other form of pubertal staging) or cognitive outcomes. Cohorts were included regardless of recruitment method or population representativeness. Cohorts with less than 500 participants were excluded (as they are unlikely to have sufficient power to examine associations between growth, puberty, cardiovascular risk and cognitive outcomes), as were cohorts that recruited participants on the basis of a pre-existing condition. Multiple papers referring to the same cohort were also excluded. Non-English language papers were not excluded, (although none were identified).

Details of cohort sample size, retention rate, birth year, data availability, and whether data were collected during mid-childhood and the perinatal period in addition to adolescence (ages 10–19) were recorded. Papers summarising the cohort profile were identified where possible. Each selected cohort was critiqued and rated good, poor or fair by two authors (JLW and KH) using the Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies provided by the U.S Department of Health and Human Services[24].

Results

We reviewed abstracts from 1829 papers, of which 1714 did not fulfil the inclusion criteria, or referred to cohorts already selected. Reviewing the full texts of the remaining 115 papers excluded a further 91 papers (Fig 1.)

We identified 24 adolescent cohorts from 12 countries across Asia (n = 10), Africa (n = 6) and South/ Central America (n = 8) (Tables 2,3 and 4). 21 cohorts were rated as “good” using the Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies (see Appendix), with 1 cohort rated “fair” (the INCAP Longitudinal Study[25]), 1 as “good/fair” (The Tsimane Amazonian Panel Study (TAPS)[26]) one as “fair/poor” (the Chinese Metabolic Syndrome Twin Cohort Study[27]). Tables 2, 3 and 4 show a summary of each cohort identified, by geographical region. 10 cohorts included variables to assess all the variables of interest (growth, puberty, cognition and cardiovascular risk): (The Mysore Parthenon Birth Cohort,[28] Cebu Longitudinal Health and Nutrition Survey[29], Pelotas (1993) Cohort[30, 31], the younger child Young Lives[32] cohorts in Vietnam, Ethiopia, Peru and India, the Birth to Twenty Cohort[33], Cape Area Panel Study(CAPS)[34] and the 1986 Jamaica Birth Cohort[35]). Of these, 2 included a broad cardiovascular risk assessment (BP, glucose and lipid profile, physical activity and anthropometry), Tanner pubertal staging, and a range of variables to assess cognition (the Birth to Twenty Cohort[33] and the Mysore Parthenon Birth Cohort[28]).

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Table 2. Characteristics of and outcomes assessed in adolescent cohorts in low and middle income countries in Asia.

https://doi.org/10.1371/journal.pone.0190443.t002

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Table 3. Characteristics of and outcomes assessed in adolescent cohorts in low and middle income countries in South America and Caribbean.

https://doi.org/10.1371/journal.pone.0190443.t003

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Table 4. Characteristics of and outcomes assessed in adolescent cohorts in low and middle income countries in Africa.

https://doi.org/10.1371/journal.pone.0190443.t004

Discussion

This systematic literature review identified 24 adolescent cohorts set in LMICs that include data on growth and pubertal timing and cognitive or cardiovascular outcomes. Although these cohorts cover 12 different LMICs, 58% were based in one of only 4 countries; India, Brazil, Vietnam and Ethiopia, and 8 (33%) were from one cross-national study (Young Lives[32]). Aside from these cohorts, we found very limited life-course data available in LMICs that include these indicators of adolescent and future adult health.

We identified ten cohorts which included variables to assess all the outcomes of interest, but only five of these included thorough cardiovascular risk. Of the two which also included Tanner pubertal staging (the Birth to Twenty Cohort[33] and the Mysore Parthenon Birth Cohort[28]), only the Birth to Twenty Cohort[33] has collected data beyond early adolescence.

The cohorts we identified were mostly of high quality, and 22 were rated “good” using the Assessment Tool for Observational Cohort and Cross-Sectional Studies. They varied in size, scope, composition and attrition rates, and were based in countries that reflect a wide range of political, economic, cultural, and social contexts. Although this heterogeneity provides a rich source of diverse data on adolescent health outcomes in these settings, this will limit generalizability. For example, the two South African cohorts identified followed children and young people growing up in a period of unique social and political change in the aftermath of Apartheid, limiting the applicability of their findings to other settings. Further, many were not nationally representative. Adolescents from higher socioeconomic groups were under-represented in Young Lives[32], Birth to Twenty[33], CAPS[34], and the 1986 Jamaica Birth Cohort[35], and were more likely to be lost to follow up in the Cebu Longitudinal Health and Nutrition Survey[29] and the Mysore Parthenon Birth Cohort[28]. As discussed, the prevalence and confounding structure of exposures pertinent to adolescent growth and puberty, and subsequent cardiovascular and cognitive risk, varies by socioeconomic group, and so generalising findings from these cohorts may be problematic.

Comparison with the literature

Our study demonstrates the pressing need for large scale longitudinal cohort studies in LMICs with long follow-up periods, as recently highlighted by Victora and Barros[45]. Their literature search of birth cohorts identified 6500 studies, but of the 20 countries with the largest number of articles, only India and Brazil were LMICs. Where cohort studies are established in these settings, they are often on a small scale with short follow up periods. A systematic review by Campbell et al[46] of birth cohorts in Sub-Saharan Africa identified 28 separate cohorts, but the majority only followed up for less than 2 years. Many were subject to high non-enrolment and attrition rates, and complicated by high rates of migration. Our findings also highlight that non-communicable disease outcomes are poorly represented in longitudinal studies involving adolescents in LMICs, similar to other reviews of cohorts outside high-income countries. A systematic review of birth cohort studies in South East Asia and Eastern Mediterranean regions found only 12 of 83 studies identified focused on non-communicable disease outcomes[47], despite the epidemiological transition shifting the burden of disease away from communicable causes in many of these countries[47].

In addition to establishing new longitudinal studies in LMIC, exploiting existing data sources should also be a priority. The challenges of sharing data sources are well described[48], but initiatives such as The Healthy Birth, Growth, and Development–Knowledge Integration (HBGDki) project[49], which has pooled data from 420 survey studies in 50 countries with the goal of improving interventions for faltering growth and neurocognitive deficits in childhood, demonstrate its potential. The Consortium of Health-Oriented Research in transitional Societies (COHORTS)[50] is a further example of the benefits of collaboration between established study groups. A wider formal network of adolescent cohorts may add insights into the unique role of this period of the life course on future non-communicable disease risk.

Strengths and limitations

We performed the first systematic literature search identifying longitudinal studies of adolescents in LMIC. We used well-defined inclusion and exclusion criteria to target studies of interest, and reviewed the reference lists of included studies to identify further cohorts. Where possible we utilised published “Cohort Profile” papers, but also accessed the original questionnaires used in the studies where necessary to establish which outcomes were included. There were a number of limitations to our study however. Studies that were initially cross sectional but then followed up at a later date may have been missed. Variables included in the cohorts we identified often change between waves of follow-up, and we may not have described the most recent summary of measurements taken. Although we critiqued the cohorts using the US. Department for Health and Human Services Quality Assessment Tool[24] in order to guide future research using the data sources we identified, multiple other methods are available and may have been more appropriate[51]. We also limited our search to MEDLINE and did not utilise other search engines, which may have biased our results or led us to miss relevant studies. However, as we were trying to identify large well-established cohorts of 500 participants or more, which are referenced in multiple studies, it is unlikely this would have yielded any additional cohorts.

Conclusion

Improving adolescent health is integral to future adult and newborn outcomes, and yet young people in LMIC continue to be under-represented in research studies[6]. The majority of cohort data identified in this study are freely available or accessible on request, and these sources should be better utilised by researchers in adolescent global health. However, our study demonstrates that additional cohort studies of adolescents in LMIC are needed to establish how exposures during this stage of the life course influence future cognitive outcomes and non-communicable disease morbidity. This should be a global development priority.

Supporting information

S1 Table. Keywords used in the literature search strategy.

https://doi.org/10.1371/journal.pone.0190443.s001

(PDF)

S2 Table. Quality assessment tool used for each cohort included in the study (the quality assessment tool for observational cohort and cross-sectional studies provided by the US department of health and Human Services).

https://doi.org/10.1371/journal.pone.0190443.s002

(PDF)

S3 Table. The PRISMA 2009 checklist for this study.

https://doi.org/10.1371/journal.pone.0190443.s003

(PDF)

S4 Table. Full list of studies identified by the literature search.

https://doi.org/10.1371/journal.pone.0190443.s004

(XLSX)

References

  1. 1. World Health Organization. Global health risks: mortality and burden of disease attributable to selected major risks: World Health Organization; 2009.
  2. 2. Sawyer SM, Afifi RA, Bearinger LH, Blakemore SJ, Dick B, Ezeh AC, et al. Adolescence: a foundation for future health. Lancet. 2012;379(9826):1630–40. Epub 2012/04/28. pmid:22538178.
  3. 3. Gore FM, Bloem PJN, Patton GC, Ferguson J, Joseph V, Coffey C, et al. Global burden of disease in young people aged 10–24 years: a systematic analysis. The Lancet. 2011;377(9783):2093–102. http://dx.doi.org/10.1016/S0140-6736(11)60512-6.
  4. 4. Lozano R, Naghavi M, Foreman K, Lim S, Shibuya K, Aboyans V, et al. Global and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a systematic analysis for the Global Burden of Disease Study 2010. The Lancet. 2013;380(9859):2095–128.
  5. 5. Patton GC, Sawyer SM, Santelli JS, Ross DA, Afifi R, Allen NB, et al. Our future: a Lancet commission on adolescent health and wellbeing. The Lancet. 2016.
  6. 6. Anthony D. The state of the world's children 2011-adolescence: an age of opportunity: United Nations Children's Fund (UNICEF); 2011.
  7. 7. Patton GC, Viner R. Pubertal transitions in health. The Lancet. 2007;369(9567):1130–9.
  8. 8. Heys M, Schooling CM, Jiang C, Adab P, Cheng KK, Lam TH, et al. Childhood growth and adulthood cognition in a rapidly developing population. Epidemiology. 2009;20(1):91–9. pmid:19244658.
  9. 9. Zhang ZX, Plassman BL, Xu Q, Zahner GE, Wu B, Gai MY, et al. Lifespan influences on mid- to late-life cognitive function in a Chinese birth cohort. Neurology. 2009;73(3):186–94. pmid:19620606; PubMed Central PMCID: PMC2843580.
  10. 10. Goddings AL, Mills KL, Clasen LS, Giedd JN, Viner RM, Blakemore SJ. The influence of puberty on subcortical brain development. NeuroImage. 2014;88:242–51. pmid:24121203; PubMed Central PMCID: PMC3991320.
  11. 11. Heys M, Jiang C, Cheng KK, Zhang W, Lam TH, Leung GM, et al. Does the age of achieving pubertal landmarks predict cognition in older men? Guangzhou Biobank Cohort Study. Ann Epidemiol. 2010;20(12):948–54. pmid:20727786.
  12. 12. Jimenez-Chillaron JC, Patti ME. To catch up or not to catch up: is this the question? Lessons from animal models. Curr Opin Endocrinol Diabetes Obes. 2007;14(1):23–9. pmid:17940415.
  13. 13. Laitinen J, Power C, Järvelin M-R. Family social class, maternal body mass index, childhood body mass index, and age at menarche as predictors of adult obesity. The American journal of clinical nutrition. 2001;74(3):287–94. pmid:11522550
  14. 14. Hardy R, Kuh D, Whincup PH, Wadsworth ME. Age at puberty and adult blood pressure and body size in a British birth cohort study. J Hypertens. 2006;24(1):59–66. pmid:16331102
  15. 15. Prentice P, Viner R. Pubertal timing and adult obesity and cardiometabolic risk in women and men: a systematic review and meta-analysis. Int J Obes. 2013;37(8):1036–43.
  16. 16. Heys M, Lin SL, Lam TH, Leung GM, Schooling CM. Lifetime growth and blood pressure in adolescence: Hong Kong's "Children of 1997" birth cohort. Pediatrics. 2013;131(1):e62–72. pmid:23230068.
  17. 17. Schooling CM, Jiang C, Lam TH, Thomas GN, Heys M, Bmbs , et al. Height, its components, and cardiovascular risk among older Chinese: a cross-sectional analysis of the Guangzhou Biobank Cohort Study. Am J Public Health. 2007;97(10):1834–41. pmid:17761579
  18. 18. Gupta PC, Ray CS. Smokeless tobacco and health in India and South Asia. Respirology. 2003;8(4):419–31. pmid:14708551.
  19. 19. Kwok MK, Schooling CM, Lam TH, Leung GM. Does breastfeeding protect against childhood overweight? Hong Kong's 'Children of 1997' birth cohort. International journal of epidemiology. 2010;39(1):297–305. pmid:19700441.
  20. 20. Marmot MG, Adelstein AM, Robinson N, Rose GA. Changing social-class distribution of heart disease. British medical journal. 1978;2(6145):1109–12. pmid:709255; PubMed Central PMCID: PMC1608272.
  21. 21. Dinsa G, Goryakin Y, Fumagalli E, Suhrcke M. Obesity and socioeconomic status in developing countries: a systematic review. Obes Rev. 2012;13(11):1067–79. pmid:22764734
  22. 22. Sletner L, Nakstad B, Yajnik CS, Morkrid K, Vangen S, Vardal MH, et al. Ethnic differences in neonatal body composition in a multi-ethnic population and the impact of parental factors: a population-based cohort study. PloS one. 2013;8(8):e73058. pmid:24009731; PubMed Central PMCID: PMC3756946.
  23. 23. World Bank Country and Lending Groups http://data.worldbank.org/about/country-and-lending-groups [Internet]. 2016 [cited 10th December 2015].
  24. 24. U.S Department of Health and Human Services National Heart Lung and Blood Institute. Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies, http://www.nhlbi.nih.gov/health-pro/guidelines/in-develop/cardiovascular-risk-reduction/tools/cohort. 2014.
  25. 25. Martorell R, Habicht J-P, Rivera JA. History and Design of the INCAP Longitudinal Study (1969–77). The Journal of Nutrition. 1995;125(4):1027.
  26. 26. Leonard WR, Reyes-García V, Tanner S, Rosinger A, Schultz A, Vadez V, et al. The Tsimane’Amazonian Panel Study (TAPS): Nine years (2002–2010) of annual data available to the public. Econ Hum Biol. 2015;19:51–61. pmid:26280812
  27. 27. Li S, Liu R, Arguelles L, Wang G, Zhang J, Shen X, et al. Adiposity trajectory and its associations with plasma adipokine levels in children and adolescents—A prospective cohort study. Obesity. 2015.
  28. 28. Krishnaveni GV, Veena SR, Hill JC, Karat SC, Fall CH. Cohort profile: Mysore parthenon birth cohort. Int J Epidemiol. 2014:dyu050.
  29. 29. Adair LS, Popkin BM, Akin JS, Guilkey DK, Gultiano S, Borja J, et al. Cohort profile: the Cebu longitudinal health and nutrition survey. Int J Epidemiol. 2010:dyq085.
  30. 30. Victora CG, Hallal PC, Araújo CL, Menezes AM, Wells JC, Barros FC. Cohort profile: the 1993 Pelotas (Brazil) birth cohort study. Int J Epidemiol. 2008;37(4):704–9. pmid:17846051
  31. 31. Gonçalves H, Assunção MC, Wehrmeister FC, Oliveira IO, Barros FC, Victora CG, et al. Cohort profile update: The 1993 Pelotas (Brazil) birth cohort follow-up visits in adolescence. Int J Epidemiol. 2014:dyu077.
  32. 32. Barnett I, Ariana P, Petrou S, Penny ME, Galab S, Woldehanna T, et al. Cohort profile: the Young Lives study. Int J Epidemiol. 2013;42(3):701–8. pmid:22617687
  33. 33. Richter L, Norris S, Pettifor J, Yach D, Cameron N. Cohort profile: Mandela's children: the 1990 Birth to Twenty study in South Africa. Int J Epidemiol. 2007;36(3):504–11. pmid:17355979
  34. 34. Lam D, Ardington C, Branson N, Case A, Leibbrandt M, Menendez A, et al. The Cape Area Panel Study: A Very Short Introduction to the Integrated Waves 1-2-3-4-5 (2002–2009) Data. Cape Town: Centre for Social Science Research, University of Cape Town. 2011.
  35. 35. McCaw-Binns A, Ashley D, Samms-Vaughan M, Wilks R, Ferguson T, Younger N, et al. Cohort profile: the Jamaican 1986 birth cohort study. Int J Epidemiol. 2011;40(6):1469–76. pmid:20805108
  36. 36. Antonisamy B, Raghupathy P, Christopher S, Richard J, Rao P, Barker DJ, et al. Cohort profile: the 1969–73 Vellore birth cohort study in South India. Int J Epidemiol. 2009;38(3):663–9. pmid:18684785
  37. 37. Kinra S, Krishna KR, Kuper H, Sarma KR, Prabhakaran P, Gupta V, et al. Cohort profile: Andhra Pradesh children and parents study (APCAPS). Int J Epidemiol. 2014;43(5):1417–24. pmid:24019421
  38. 38. Trang NHHD Hong TK, Dibley MJ. Cohort profile: Ho Chi Minh City Youth Cohort—changes in diet, physical activity, sedentary behaviour and relationship with overweight/obesity in adolescents. BMJ open. 2012;2(1):e000362. pmid:22337814
  39. 39. Victora CG, Barros FC. Cohort profile: the 1982 Pelotas (Brazil) birth cohort study. Int J Epidemiol. 2006;35(2):237–42. pmid:16373375
  40. 40. Cardoso VC, Simões V, Barbieri MA, Silva AAMd, Bettiol H, Alves M, et al. Profile of three Brazilian birth cohort studies in Ribeirão Preto, SP and São Luís, MA. Braz J Med Biol Res. 2007;40(9):1165–76. pmid:17713669
  41. 41. Belachew T, Hadley C, Lindstrom D, Getachew Y, Duchateau L, Kolsteren P. Food insecurity and age at menarche among adolescent girls in Jimma Zone Southwest Ethiopia: a longitudinal study. Reprod Biol Endocrinol. 2011;9(1):1.
  42. 42. Hadley C, Belachew T, Lindstrom D, Tessema F. The forgotten population? Youth, food insecurity, and rising prices: implications for the global food crisis. NAPA bulletin. 2009;32(1):77–91. pmid:24489524
  43. 43. Brown University, Jimma University. Jimma Longitudinal Family Survey of Youth (JLFSY) Study Design 2015.
  44. 44. De Weerdt J, Beegle K, Lilleør HB, Dercon S, Hirvonen K, Kirchberger M, et al. Kagera health and development survey 2010: Basic information document. Rockwool Foundation Working Paper Series, 2012.
  45. 45. Victora CG, Barros FC. Cohorts in Low-and Middle-Income Countries: From Still Photographs to Full-Length Movies. The Journal of Adolescent Health. 2012;51(6):S3.
  46. 46. Campbell A, Rudan I. Systematic review of birth cohort studies in Africa. Journal of Global Health. 2011;1(1):46–58. PubMed PMID: PMC3484737. pmid:23198102
  47. 47. McKinnon R, Campbell H. Systematic review of birth cohort studies in South East Asia and Eastern Mediterranean regions. Journal of global health. 2011;1(1):59–71. pmid:23198103
  48. 48. Longo DL, Drazen JM. Data sharing. N Engl J Med. 2016;374(3):276–7. pmid:26789876
  49. 49. Jumbe NLn, Murray JC, Kern S. Data Sharing and Inductive Learning—Toward Healthy Birth, Growth, and Development. N Engl J Med. 2016.
  50. 50. Richter LM, Victora CG, Hallal PC, Adair LS, Bhargava SK, Fall CH, et al. Cohort profile: the consortium of health-orientated research in transitioning societies. Int J Epidemiol. 2012;41(3):621–6. Epub 2011/01/13. pmid:21224276; PubMed Central PMCID: PMCPMC3378468.
  51. 51. Sanderson S, Tatt ID, Higgins J. Tools for assessing quality and susceptibility to bias in observational studies in epidemiology: a systematic review and annotated bibliography. Int J Epidemiol. 2007;36(3):666–76. pmid:17470488