Malnutrition rates remain alarming: stunting is declining too slowly while wasting still impacts the lives of far too many young children
Nearly half of all deaths in children under 5 are attributable to undernutrition, translating into the loss of about 3 million young lives a year. Undernutrition puts children at greater risk of dying from common infections, increases the frequency and severity of such infections, and delays recovery.
The interaction between undernutrition and infection can create a potentially lethal cycle of worsening illness and deteriorating nutritional status. Poor nutrition in the first 1,000 days of a child’s life can also lead to stunted growth, which is associated with impaired cognitive ability and reduced school and work performance.
Resources
Notes on the data
Indicators
|
Indicator name |
Definition |
||
|---|---|---|---|
|
Numerator |
Denominator |
Colloquial definition |
|
| Stunting | Number of under-fives falling below minus 2 standard deviations (moderate and severe) and minus 3 standard deviations (severe) from the median height-for-age of the reference* population | Children under 5 years of age in the surveyed population | Stunting refers to a child who is too short for his or her age. These children can suffer severe irreversible physical and cognitive damage that accompanies stunted growth. The devastating effects of stunting can last a lifetime and even affect the next generation. |
| Wasting | Number of under-fives falling below minus 2 standard deviations (moderate and severe) and minus 3 standard deviations (severe) from the median weight-for-height of the reference* population | Children under 5 years of age in the surveyed population | Wasting refers to a child who is too thin for his or her height. Wasting is the result of recent rapid weight loss or the failure to gain weight. A child who is moderately or severely wasted has an increased risk of death, but treatment is possible. |
| Overweight | Number of under-fives above 2 standard deviations from the median weight-for-height of the reference* population | Children under 5 years of age in the surveyed population | Overweight refers to a child who is too heavy for his or her height. This form of malnutrition results from energy intakes from food and beverages that exceed children’s energy requirements. Overweight increases the risk of diet-related noncommunicable diseases later in life. |
*The reference population is based on the WHO Child Growth Standards, 2006
Please note that some children can suffer from more than one form of malnutrition – such as stunting and overweight or stunting and wasting. There are currently no joint global or regional estimates for these combined conditions, but UNICEF has a country-level dataset with country level estimates, where re-analysis was possible.
Growth standard (reference population)
Prevalence of stunting, wasting and overweight among children under 5 is estimated by comparing actual measurements to an international standard reference population. In April 2006, the World Health Organization (WHO) released the WHO Child Growth Standards to replace the widely used National Center for Health Statistics (NCHS)/WHO reference population, which was based on a limited sample of children from the United States of America. The new standards are the result of an intensive study project involving more than 8,000 children from Brazil, Ghana, India, Norway, Oman and the United States. Overcoming the technical and biological drawbacks of the old reference population, the new standards confirm that children born anywhere in the world and given the optimum start in life have the potential to reach the same range of height and weight. It follows that differences in children’s growth to age 5 are more influenced by nutrition, feeding practices, environment and health care than by genetics or ethnicity.
The new standards should be used in future assessments of child nutritional status. It should be noted that because of the differences between the old reference population and the new standards, prevalence estimates of child anthropometry indicators based on these two references are not readily comparable. It is essential that all estimates are based on the same reference population (preferably the new standards) when conducting trend analyses.
Adjusting country-level estimates
Before conducting trend analyses of child nutritional status, it is important to ensure that estimates from various data sources are comparable over time. For example, household surveys in some countries in the early 1990s only collected child anthropometry information among children up to 47 months of age – or even up to only 35 months of age. Prevalence estimates based on such data only referred to children under 4 or under 3 years of age and are not comparable to prevalence estimates based on data collected from children up to 59 months of age. Some age adjustment needs to be applied to make these estimates based on non-standard age groups comparable to those based on the standard age range. For more information about age adjustment, please click here to read a technical note. In addition, prevalence estimates need to be calculated according to the same reference population. Those calculated according to the WHO Child Growth Standards are not comparable to those calculated according to the NCHS/WHO reference population. For more information about the difference between the two references and its implications, please click here to read a series of questions and answers.
Assigning years to surveys
When data collection begins in one calendar year and continues into the next, the survey year assigned is the one in which most of the fieldwork took place. For example, if a survey was conducted between 1 September 2009 and 28 February 2010, the year 2009 would be assigned, since the majority of data collection took place in that year (i.e., four months in 2009 versus two months in 2010). This method has been used since the 2013 edition (prior to that, the latter year was used by default – e.g., 2010 in the example above).
Final reports only
As of the 2014 edition, the country-level dataset used to generate the global and regional joint malnutrition estimates is based only on final survey results. Preliminary survey results are no longer included in the dataset since the data are sometimes retracted or change significantly when the final version is released.
Estimating country-level progress
Country-level progress in reducing undernutrition prevalence is evaluated by calculating the average annual rate of reduction (AARR) and comparing this to the AARR needed in order to achieve targets. For more information about how to calculate country-level AARR, please click here to read a technical note. A Nutrition Targets Tracking Tool which provides AARR levels for different scenarios is also available to investigate progress towards the 2025 WHA nutrition targets for each country.
Estimating regional trends by multi-level modelling
Estimation of regional and global trends is based on a multilevel modelling method (see de Onis et al. in JAMA, 2004). For the most recent trend analysis, a total of 837 data points from 150 countries over the period 1983 to 2017 were included in the model. This set of trend data points was jointly reviewed by UNICEF, WHO and the World Bank Group in January 2018 to ensure that it is nationally representative of under-five children, processed using standard algorithms and comparable vertically and horizontally. Global and regional trend modelling and graphing were carried out using SAS (the country-level data set and analysis code are available on request).
Model-based trend analysis of underweight prevalence (percentage), by region
How to read this chart:
Each circle represents a prevalence estimate from a country for one survey. The size of the circle is proportional to the under-five population in that country for the average of all survey years. The solid line indicates the regional trend as modelled on all the available data points in the region.
Other notes on Joint Malnutrition Estimates
1. Explanation as to why trends are shown for stunting and overweight but only most current estimate for wasting and severe wasting: Prevalence estimates for stunting and overweight are relatively stable over the course of a calendar year. It is therefore possible to track global and regional changes in these two conditions over time. Wasting and severe wasting are acute conditions that can change frequently and rapidly over the course of a calendar year. This makes it difficult to generate reliable trends over time with the input data available, and as such, this report provides only the most recent global and regional estimates (2017 for the JME 2018 edition).
The joint global and regional estimates that make up the UNICEF/ WHO/World Bank Group Joint Child Malnutrition Estimates have been generated using a country-level dataset which is mainly comprised of estimates from nationally representative household surveys. These data are collected infrequently (every 3 to 5 years in most countries) and measure malnutrition at one point in time (e.g. during one or several months of field work), making it difficult to capture the rapid fluctuations in wasting that can occur over the course of a given year. Incidence data (i.e. the number of new cases that occur during the calendar year) would allow for better tracking of changes over time; however, these data currently do not exist.
2. Footnotes on population coverage
As started in the 2014 edition, a separate exercise was conducted to assess population coverage. This was important in order to alert the reader, via footnotes, to instances where the data should be interpreted with caution due to low population coverage (defined as less than 50 per cent). A conservative method was applied looking at available data within mutually exclusive five-year periods around the projected years. Population coverage was calculated as:
3. Prevalence thresholds for wasting, overweight and stunting in children under 5 years
New thresholds, presented in the table below, were established through the WHO-UNICEF Technical Advisory Group on Nutrition Monitoring (TEAM)2 and have been used for development of prevalence-based maps. The thresholds were developed in relation to standard deviations (SD) of the normative WHO Child Growth Standards. The international definition of ‘normal’ (two SD from the WHO standards median) defines the first threshold, which includes 2.3% of the area under the normalized distribution. Multipliers of this “very low” level (rounded to 2.5%) set the basis to establish subsequent thresholds.
Prevalence thresholds (%) for severity of malnutrition among children under 5 years
| Labels | Prevalence thresholds (%) for: | ||
| Wasting | Overweight | Stunting | |
| Very low | <2.5 | <2.5 | <2.5 |
| Low | 2.5 – <5 | 2.5 – <5 | 2.5 – <10 |
| Medium | 5 – <10 | 5 – <10 | 10 – <20 |
| High | 10 – <15 | 10 – <15 | 20 – <30 |
| Very high | ≥15 | ≥15 | ≥30 |
de Onis, Mercedes et al. (2018) Prevalence thresholds for wasting, overweight and stunting in children under 5 years. (Manuscript submitted for publication.)