Growth in the first 1000 days lays the foundation for human capital formation

Two articles in this issue of the American Journal of Clinical Nutrition demonstrate that performance on standardized intelligence quotient (IQ) tests at ages 5 and 18 y can be predicted by birth weight, length, and early growth (1, 2). The studies, set in Brazil and Denmark, highlight the long-term relationship of nutritional adequacy in the first 1000 d (from conception to the second birthday) with intelligence, a key component of human capital. These insights can inform population-level strategies to foster intelligence and evoke research questions on mechanisms linking early nutrition with human capital.

In the Brazil study, the association between IQ at age 18 y and conditional height was strongest at age 12 mo, significant but attenuated at age 4 y, and absent at ages 11, 15, and 18 y. The Danish study found that IQ at age 5 y was significantly associated with birth weight and weight gain in early infancy and was mediated through greater weight at 12 mo, but was not associated with weight gain from 12 mo to 5 y. Taken together, these findings highlight that childhood and adolescent IQ are predicted by growth patterns established prenatally and extending into the first year.

Neither the Brazil nor the Denmark study examined the second year (ages 12–24 mo). During this period of complementary feeding and transition to the family diet, the rate of physical growth declines as brain development continues. Physical activity and autonomy increase, accompanied by exploration, impulsivity, and neophobia (hesitation to try new foods). These developmental changes create increased risks of infections and nutritional deficiencies. Future research could examine how changes in nutritional status during this period relate to subsequent growth and IQ.

Findings in these studies are consistent with research showing that recovery in linear growth (height) beyond the age of 2 y is not associated with corresponding increases in intelligence (3). Studies using latent variables and structural equation models have found stability in intelligence across infancy, early childhood, childhood, and adolescence (4). Advances in intelligence occur through a predictable sequence of increasingly complex interdependent learning processes, with early learning serving as a building block for subsequent learning. Early adversities affect intelligence, which in turn reduces the subsequent ability to learn, causing disparities. Thus, investments in promoting early intellectual functioning are likely to yield strong and long-lasting individual and societal benefits.

Brazil and Denmark are middle- and high-income countries, respectively, with universal health systems. Mothers of children in the Brazilian cohort had access to a Unified Health System (Sistema Único de Saúde), established with the goal of promoting equality of opportunities and universal health care. Likewise, mothers of children in the Danish cohort had access to a high-quality tax-funded health-care system. The relatively low prevalences of infants with birth weights under 2500 g (4.6% in Denmark and 8.7% in Brazil), compared with the global estimated prevalence of 14.6% in 2015 (5), may be partially attributed to the universal health-care systems, along with adequate maternal nutrition before and during pregnancy. The finding that associations between birth weight and intellectual performance extend to healthy populations and are not limited to extremes, such as intrauterine growth restriction, add to the urgency of developing strategies to ensure access to prenatal care and to support healthy maternal diets and prenatal growth.

In addition to intelligence, human capital formation includes health, well-being, happiness, and economic sufficiency: characteristics that enable children to thrive as adults, contribute to society, and provide a secure environment for themselves, their families, and future generations (6). Human capital is formed over the life course, beginning prior to conception with the health and well-being of both parents and extending through the prenatal period, childhood, and adolescence, and into early adulthood. The first 1000 d is a period of plasticity, marked by the genesis of multi-organ systems, including brain formation and functioning. Nutrition is frequently linked to critical periods of heightened sensitivity during early development. Fetal and infant growth and development may be susceptible to vulnerabilities associated with biological exposures, such as nutritional deficiencies, infections, or toxic exposures, or psychosocial exposures, such as stress, lack of nurturing care, or neglect. Conversely, positive biological, social, and environmental exposures promote human development and may mitigate early adversities and lessen gaps in human capital attainment.

To understand the pathways leading to human capital formation, good nutrition, although critical, is not sufficient. Based on principles of nurturing care, early and consistent access to health care, nutrition, responsive caregiving, learning opportunities, and safety and security interact to promote human capital development (7). An observational study across 4 low- and middle-income countries found that intellectual performance at ages 4–8.5 y was predicted primarily by parental capacities and economic resources, rather than by birth weight and early linear growth (8). Nurturing care may also attenuate the negative impact of early adversities, as shown in an observational study conducted in Brazil and South Africa. Nurturing interactions during preschool ages mitigated the negative effect of cumulative early adversities on adolescent IQs (9). Additional evidence comes from a home visiting intervention that provided learning opportunities for children in Jamaica who were stunted, resulting in significant gains in intelligence and school performance through adolescence and increased earnings in adulthood (10). In addition to nutrition, intelligence is related to social class, exposure to cumulated adversities, parental nurturance, and educational and other learning opportunities (11). Programs and services based on nurturing care can facilitate growth and development throughout childhood and adolescence, as well as protect children from the negative consequences of early adversities.

Nutrition influences human capital development, particularly during the first 1000 d. Although a lack of adequate nutrition can hinder learning, nutrition-based interventions alone have had limited impact on children's development (12). As children grow and develop, nutrition may impact human capital through synergistic interactions with the other components of nurturing care. Additional research is needed to increase the understanding of nutrition's impact beyond the age of 12 mo, including the mechanisms linking nutrition to IQ and other aspects of human capital. In summary, policies and programs are needed to advance pre- and postnatal health and nutrition to build a strong foundation during the first 1000 d, along with opportunities for nurturing care throughout childhood and adolescence, to ensure that all children have opportunities to meet their human capital potential.

Notes

This work was supported by the National Institute of Diabetes, Digestive, & Kidney Disorders (R01 DK107761).