What is childhood stunting?
Defining Childhood Stunting
Childhood stunting is the failure of a child to reach his or her full growth potential as a result of long-term poor diet, health, and/or care, including emotional support. It is identified and measured based on a child’s height given her age. Stunting is so consequential because it is a marker of a child’s overall lack of health and well-being. Stunting is associated with limits to a child’s physical and cognitive potential.
Stunting is caused by factors throughout childhood, but primarily during what is called “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. These physical and cognitive consequences are largely irreversible, despite parents’ best efforts later in the child’s life. Stunting itself cannot be treated, only prevented. While there is ongoing debate about the importance of stunting as an outcome itself versus as a marker of other challenges, the importance of addressing the drivers of stunting is indisputable.1
A child is considered stunted if his or her height-for-age Z-score, or “HAZ score”, is more than two standard deviations below the 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 as a measure of 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 (149 million children) were classified as stunted in 2018 .2 About 91 percent of these stunted children are clustered in low- and lower middle-income countries.3,4 South Asia has the most stunted children in the world, with two out of five of all stunted children living in the region. While stunting prevalence has declined in every region since 2000, 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
At the individual level, stunted growth is indicative of a lower developmental ceiling. When widespread, it handicaps a community’s potential.
Stunted growth casts a shadow over a child’s future. Stunting is a strong marker of lifelong reduced cognitive abilities and poor health. Compared to a healthy child, a stunted child is more likely to have poorer educational outcomes, earn lower wages, and have children who are themselves poorly nourished.- Prendergast AJ, Humphrey J H5
Multiplied by millions of children across a geographic area, stunting increases health costs, handicaps economic productivity, and limits national growth. Recent studies have estimated that the health and child development challenges associated with stunting can cost countries between 4 and 11 percent of their gross domestic product (GDP) annually. Countries with high rates of stunting are, by virtue of their poorly educated and less healthy workforces, less equipped to compete in the knowledge economy.6 Countries with high stunting prevalence, also burdened by less educated and healthy workforces, are less 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 women8 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|
Height as an indicator of child well-being is a relatively new concept. Small babies and short children and adults were once seen as merely 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 in low-resource settings, smaller children often faced a constellation of health and development challenges. They came to interpret short stature as “nutritional growth failure,” a critical indicator of a child’s physical and cognitive well-being. They dubbed this growth failure “childhood stunting."10
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. Stunting remains a powerful but complex measurement – a single data point that captures the nutritional status of a child and the long-term health, wealth, and equity of a population.
The World Health Organization (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 and another based on bottle-fed babies in Ohio.11 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 sub-national growth charts for different ethnicities within a given country? These questions prompted the 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 Multi-centre Growth Reference Study (MGRS), conducted from 1997 to 2003, did just that.12 It followed approximately 8,500 children from widely different settings in Brazil, Ghana, India, Norway, Oman, and the USA. 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 and followed best practices in health care, such as exclusive breastfeeding and avoidance of smoking.
|The findings of the study were a revelation: all children, regardless of ethnicity or heritage, experience similar linear growth patterns through age five if their nutritional and health needs are met.|
That all children have the same potential for growth was reinforced by a second study, done by the International Fetal and Newborn Growth Consortium for the 21st century (INTERGROWTH-21st). Using similar methods to the MGRS study, INTERGROWTH‐21st measured fetal growth and newborn nutritional status. The study was a response to mounting evidence that growth during a child’s first 1,000 days (from pre-conception to the age of two) is especially important as a predictor of future life outcomes.
INTERGROWTH-21st confirmed the findings of the MGRS 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 environmental constraints on growth, such as a mother’s own history of poor nutrition or small size, are limited.13
|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 World Health Organization Child Growth Standards, released in 2006, are based on these two studies and the new universal expectations for child growth.
The WHO Child Growth Standards median applies in the same way across populations and ethnic groups worldwide.5 It is as applicable to children in geographies known for short stature as it is in geographies known for tall stature. It is as apt a measure of health and nutrition for a newborn as it is for a two-year-old.14
That said, these growth standards are more useful as a measure of a population’s health and nutritional status than as a measure for an individual child. Two toddlers of the same age who are a few millimeters apart, one on one side of the cut off and one on the other side, may be classified differently. Biologically, however, they would be similar in terms of nutritional status. Thus there is little biological basis for a precise "standard deviation cutoff to define stunting in an individual."15 It is an arbitrary threshold useful for analyzing large groups of children.
- 1Leroy JL, Frongillo EA, Perspective: What Does Stunting Really Mean? A Critical Review of the Evidence, Advances in Nutrition, 2019;10(2):196–204, https://doi.org/10.1093/advances/nmy101. Accessed May 9, 2019.
- 2UNICEF-WHO-The World Bank Group. Joint child malnutrition estimates - Levels and trends (2019 edition). World Health Organization. https://www.who.int/nutgrowthdb/estimates2018/en/. Updated March 2019. Accessed 11 May 2019.
- 3Development Initiatives, 2017. Global Nutrition Report 2017: Nourishing the SDGs. Bristol, UK: Development Initiatives. https://globalnutritionreport.org/reports/2017-global-nutrition-report/.
- 4United Nations Children’s Fund (UNICEF), World Health Organization, International Bank for Reconstruction and Development/The World Bank. Levels and trends in child malnutrition: key findings of the 2019 Edition of the Joint Child Malnutrition Estimates. Geneva: World Health Organization; 2019 Licence: CC BY-NC-SA 3.0 IGO. https://www.who.int/nutgrowthdb/jme-2019-key-findings.pdf?ua=1.
- 5Prendergast AJ, Humphrey JH. The stunting syndrome in developing countries. Paediatrics and International Child Health. 2014;34(4):250-265. doi:10.1179/2046905514Y.0000000158. https://www.tandfonline.com/doi/pdf/10.1179/2046905514Y.0000000158?needAccess=true.
- 6World Bank Group. Reaching the Global Target to Reduce Stunting: How Much Will it Cost and How Can we Pay for it? World Bank. http://pubdocs.worldbank.org/en/460861439997767818/Stunting-Costing-and-Financing-Overview-Brief.pdf. Accessed August 2017.
- 7Food and Agriculture Organization of the United Nations. State of Food and Agriculture 2013: Food systems for better nutrition. http://www.fao.org/3/i3300e/i3300e.pdf. 2013 Rome, Italy.
- 8McGovern 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. doi:10.1093/ije/dyx017. https://academic.oup.com/ije/article/46/4/1171/3095890.
- 9Galassa E, Wagstaff A, Naudeau S, Shekar M. The Economic Costs of Stunting and How to Reduce Them. World Bank Group. http://pubdocs.worldbank.org/en/536661487971403516/PRN05-March2017-Economic-Costs-of-Stunting.pdf. 22 September 2016.
- 10Waterlow JC. Classification and definition of protein-calorie malnutrition. Br Med J. 1972;3(5826):566–569. doi:10.1136/bmj.3.5826.566. https://www.bmj.com/content/bmj/3/5826/566.full.pdf.
- 11Garza C, de Onis M. Rational for developing a new international growth reference. Food and Nutrition Bulletin. 2004; 25(1). https://www.who.int/childgrowth/mgrs/en/fnb_rationale_p5_14.pdf?ua=1.
- 12The WHO Multicentre Growth Reference Study (MGRS). The WHO Website. https://www.who.int/childgrowth/mgrs/en/. Accessed May 9, 2019.
- 13Villar J, Ismail LC, Victora CG, Ohuma EO, Bertino E, Altman DG, 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. The Lancet 2014; 384(9946): e857-868. DOI: https://doi.org/10.1016/S0140-6736(14)60932-6.
- 14de Onis M., Onyango A.W., Borghi E., Garza C., Yang H. & the WHO Multicentre Growth Reference Study Group (2006a) Comparison of the WHO Child Growth Standards and the NCHS/WHO international growth reference: implications for child health programmes. Public Health Nutrition 9, 942–947.
- 15Perumal, N., Bassani, D. G., & Roth, D. E. (2018). Use and misuse of stunting as a measure of child health. The Journal of nutrition, 148(3), 311-315.