Patterns of growth in childhood in relation to adult schooling attainment and IQ in 6 birth cohorts in low and middle-income countries: evidence from COHORTS

SummaryBackgroundGrowth faltering has been associated with poor intellectual performance. The relative strengths of associations between growth in early and in later childhood remain underexplored. We examined the association between growth in childhood and adolescence and adult human capital in five low- or middle-income countries (LMICs).MethodsWe analyzed data from six prospective birth cohorts of five LMICs (Brazil, Guatemala, India, the Philippines, and South Africa). We assessed the associations of measures of height and relative weight at four ages (birth, at around age 2 years, mid-childhood (MC), adulthood), with two dimension of adult human capital (schooling attainment and IQ).FindingsIn site- and sex-pooled analyses, size at birth and linear growth from birth to around 2 years of age were positively associated with schooling attainment and adult IQ. Linear growth from age 2 years to MC and from MC to adulthood was not associated with higher school attainment or IQ. Change in relative weight in early childhood was not associated with either outcome. Relative weight in MC and in adulthood were inversely associated with schooling attainment but were not associated with adult IQ.InterpretationLinear growth in the first 1,000 days is a predictor of schooling attainment and IQ in adulthood in LMICs. Linear growth in later periods was not associated with either of these outcomes. Changes in relative weight had inconsistent association with schooling and IQ in adulthood.FundingBill and Melinda Gates Foundation (OPP1164115)Research in contextEvidence before this studyEarly life growth faltering has been associated with poor cognitive and intellectual performance in childhood and poorer schooling outcomes in children and adults. There is a paucity of data about how growth in specific age intervals over the course of childhood and adolescence relates to attained schooling and adult cognitive performance.We conducted a literature search using the terms (growth [Title/Abstract]) AND ((school [Title/Abstract] OR schooling [Title/Abstract]) AND (intelligence [Title/Abstract] OR IQ [Title/Abstract]) OR (human capital [Title/Abstract]) in Pubmed. The search yielded 536 publications from 1965 to 2020. We screened titles and selected 31 publications that included linear growth and our outcomes of interest, namely school attainment and intelligence quotient (IQ). Additionally, we checked reference lists of selected articles and identified eleven papers that were not displayed in the initial electronic query. We therefore reviewed 42 abstracts and identified 24 unique studies conducted in low and middle-income countries (LMICs). Fourteen of them investigated the association of birth size and/or early-life size with schooling or IQ, or with both outcomes during childhood. Three studies investigated the association between linear growth in early childhood and schooling and intelligence in adults, one studied the association between early-life undernutrition and IQ in early adulthood and another six publications investigated the association between growth and school attainment in adults. Economists have also studied the relationship between stunting or linear growth and schooling in LMICs, but to our knowledge not the relative importance of growth during specific age intervals.Added value of this studyThis is an analysis of the associations between child and adolescent growth and two dimensions of human capital (schooling attainment and IQ) in adulthood in six birth cohorts from five LMICs. The evidence of long-term associations of linear growth with adult IQ is scarce and the few published studies have analyzed data from a single country. In the present study, we found that size at birth and linear growth from birth to around 2 years of age were positively associated with both schooling and IQ in adulthood. Linear growth between early and mid-childhood (MC)was not associated with higher school attainment or IQ in adjusted models. Linear growth from MC to adulthood was not associated with IQ in men or women, and was inversely associated with schooling attainment in women only. Change in relative weight in early childhood was positively associated with schooling attainment only in minimally adjusted models. Relative weight measures in MC and adulthood were inversely associated with schooling attainment. Change in relative weight between MC and adulthood was not associated with adult IQ.Implications of all the available evidenceWe confirmed in multiple cohorts that birth size and linear growth from birth to age 2 years are predictors of schooling attainment and adult IQ. Linear growth in early life was the strongest predictor of these two human capital dimensions in adulthood among individuals in LMICs. We did not find evidence that supports the notion that linear growth in adolescence contributes to a better cognitive performance in adulthood. Thus, our results inform the more effective timing of nutritional and other interventions to improve linear growth and human capital in the long-term.