What is child stunting?
Defining Child Stunting
Child stunting is the failure of children to reach their full growth potential as a result of long-term poor diet, health, and/or care, including emotional support.1 Stunting is identified and measured based on children’s height in relation to their age. It is a marker of a child’s overall lack of health and well-being, and is associated with limits to a child’s physical and cognitive potential.
Stunting is caused by factors throughout childhood, but primarily during the “first 1,000 days”—the period just before conception (when the mother’s nutritional status is of paramount importance) to a child’s second birthday. The impact of the poor diet, health, and care that lead to stunting, however, lasts far beyond childhood. The physical and cognitive consequences are largely irreversible, despite parents’ best efforts later in the child’s life. For the most part, stunting itself cannot be treated, only prevented. While there is ongoing debate about the importance of stunting as an outcome in itself versus a marker of other challenges, the importance of addressing the drivers of stunting is indisputable.2
A child is considered stunted if their height-for-age z-score is more than two standard deviations below the World Health Organization (WHO) Child Growth Standards median. This cutoff is a statistical metric rather than a biological condition; children just above and below the cutoff face similar risks. As such, these growth standards are more useful as a measure of a population’s health and nutritional status than for an individual child.
HAZ scores: normal distribution
The scale of the challenge
Percentage of children under the age of 5 who are stunted
An estimated 22 percent of children under five (144 million children) were classified as stunted in 2020. About 87 percent of these stunted children are clustered in low- and lower-middle-income countries.3 South Asia has the highest number of stunted children in the world, with nearly two out of five of all stunted children living in the region. While stunting prevalence has declined globally from 33 percent in 2000 to 22 percent in 2020, progress has been uneven, and the absolute burden has remained high (it has even increased in Africa as a result of population growth).
Implications for Individuals and Societies
Stunted growth casts a shadow over a child’s future. Child stunting is strongly associated with lifelong reduced cognitive abilities and poor health. Compared with a healthy child, a stunted child is more likely to have poorer educational outcomes, earn lower wages, and eventually have children who are themselves poorly nourished.4
Multiplied by thousands or millions of children in a country, stunting is associated with increased health costs and reduced economic growth. Studies have estimated that the child health and development challenges associated with stunting can cost countries between 2 and 10 percent of their gross domestic product (GDP) annually.5 Countries with high stunting prevalence, also burdened by less educated and healthy workforces, are inadequately equipped to compete in the knowledge economy.
The estimated impact of malnutrition on the global economy could be as high as US$3.5 trillion per year, or US$500 per individual.7
A 1-cm increase in stature is associated with a 4 percent increase in wages for men and a 6 percent increase in wages for women 5 and—the per capita income penalty a country incurs for not having eliminated stunting when today’s workers were children is around 7 percent.
|Countries in Africa and South Asia incur larger penalties – around 9–10 percent of GDP per capita.9
- The estimated impact of malnutrition on the global economy could be as high as US$3.5 trillion per year, or US$500 per individual.6
- A 1 -cm increase in stature is associated with a 4 percent increase in wages for men and a 6 percent increase in wages for women6 and –— the per capita income penalty a country incurs for not having eliminated stunting when today’s workers were children is around 7 percent.7
- Countries in Africa and South Asia incur larger penalties –— around 9 to -10 percent of GDP per capita. 5
Height as an indicator of children’s well-being is a relatively new concept. Small babies and short children and adults were once merely seen as small or short. Their stature was widely understood to be the natural expression of cultural lineage or genetic inheritance. While this may be true in wealthy contexts, by the 1970s, researchers recognized that smaller children often faced a constellation of health and development challenges, especially in low-resource settings. They came to interpret short stature as “nutritional growth failure,” a critical indicator of a child’s physical and cognitive well-being. They referred to this growth failure as “child stunting." 8
Once scientists recognized linear growth as a window into children’s health and a relatively accurate marker of inequalities in human development, they sought to quantify it.
WHO used a succession of child growth reference standards to help health care providers diagnose stunting. Among these were one set of standards based on a small group of primarily European-descended children in Boston, Massachusetts, and another based on bottle-fed babies in Ohio.9 These samples, biased by ethnicity, socioeconomic status, and geography were widely recognized as inappropriate for global measurements, but there were questions about what to replace them with. Would each country need to develop its own growth chart? Would we need to develop subnational growth charts for different ethnicities within a given country? These questions prompted WHO to launch an international study to test the feasibility of a single international standard for physiological growth for all children from birth to five years old.
The WHO Multicentre Growth Reference Study, conducted from 1997 to 2003, did just that.10 It followed approximately 8,500 children from widely different settings in Brazil, Ghana, India, Norway, Oman, and the United States. Despite their geographic distribution, the children shared a few key characteristics: they were from relatively high-income families that had access to good nutrition and health care. They also followed best practices in health care, such as exclusive breastfeeding and avoidance of smoking.
That all children have the same potential for growth was reinforced by a second study, conducted by the International Fetal and Newborn Growth Consortium for the 21st century (INTERGROWTH-21st).11 It was a response to mounting evidence that growth during a child’s first 1,000 days (from preconception to the age of two) is especially important as a predictor of future life outcomes.
INTERGROWTH-21st confirmed the findings of the WHO Multicentre Growth Reference Study and confirmed that stunting starts in utero. It showed that fetal and newborn growth in length are similar across diverse geographic settings when mothers’ nutritional and health needs are met and there are few or no environmental constraints on growth, such as a mother’s own history of poor nutrition or small size.
Indeed, researchers have come to understand that differences in average height between nationalities and ethnic groups, at least in childhood, are primarily an expression of environmental constraints. Height varies far more within populations than between them.
The WHO Child Growth Standards, released in 2006, are based on these two studies and the new universal expectations for child growth.
Therefore, the WHO Child Growth Standards median applies in the same way across populations and ethnic groups worldwide.3 It is as apt a measure of child health and nutrition for a newborn as it is for a two-year-old.12
However, these growth standards are more useful as a measure of a population’s health and nutritional status than for an individual child.
WHO Malnutrition Health Topic. World Health Organization website https://www.who.int/health-topics/malnutrition#tab=tab_1. Published June 9th 2021. Accessed September 20, 2021
Leroy JL, Frongillo EA. Perspective: What does stunting really mean? A critical review of the evidence. Adv Nutr. 2019;10(2):196-204. https://doi.org/10.1093/advances/nmy101
UNICEF, World Health Organization (WHO), The World Bank Group. Joint Child Malnutrition Estimates: Levels and Trends in Child Malnutrition: Key Findings of the 2020 Edition. Geneva: WHO; 2020. Accessed July 8, 2021. https://www.who.int/publications/i/item/jme-2020-edition
Prendergast AJ, Humphrey JH. The stunting syndrome in developing countries. Paediatr Int Child Health. 2014;34(4):250-265. https://doi.org/10.1179/2046905514Y.0000000158
Galassa E, Wagstaff A, Naudeau S, Shekar M. The Economic Costs of Stunting and How to Reduce Them. Washington, DC: World Bank Group; 2017. Accessed July 9, 2021. https://www.worldbank.org/en/research/brief/policy-research-note-no5-the-economic-costs-of-stunting-and-how-to-reduce-them
Food and Agriculture Organization of the United Nations (FAO). State of Food and Agriculture 2013: Food Systems for Better Nutrition. Rome: FAO; 2013. Accessed July 8, 2021. http://www.fao.org/3/i3300e/i3300e.pdf
McGovern ME, Krishna A, Aguayo VM, Subramanian SV. A review of the evidence linking child stunting to economic outcomes. Int J Epidemiol. 2017;46(4):1171-1191. https://doi.org/10.1093/ije/dyx017
Waterlow JC. Classification and definition of protein-calorie malnutrition. Br Med J. 1972;3(5826):566-569. https://doi.org/10.1136/bmj.3.5826.566
Garza C, de Onis M. Rationale for developing a new international growth reference. Food Nutr Bull. 2004;25(1). https://www.who.int/childgrowth/mgrs/en/fnb_rationale_p5_14.pdf
WHO Multicentre Growth Reference Study. The World Health Organization website. Accessed July 8, 2021. https://www.who.int/tools/child-growth-standards/who-multicentre-growth-reference-study
Villar J, Ismail LC, Victora CG, et al. International standards for newborn weight, length, and head circumference by gestational age and sex: the Newborn Cross-Sectional Study of the INTERGROWTH-21st Project. Lancet. 2014;384(9946): e857-868. https://doi.org/10.1016/S0140-6736(14)60932-6
de Onis M, Onyango AW, Borghi E, Garza C, Yang H, WHO Multicentre Growth Reference Study Group. Comparison of the WHO Child Growth Standards and the NCHS/WHO international growth reference: implications for child health programmes. Public Health Nutr. 2006;9(7):942-947. https://doi.org/10.1017/phn20062005