Malnutrition can arise in three forms:
- hunger and undernourishment, which is defined as dietary energy intakes below the minimum levels necessary to achieve and maintain a healthy weight;
- obesity or overnourishment, which is defined as dietary energy intake which exceeds requirements for maintenance of a healthy bodyweight;
- micronutrient deficiencies, which is defined as a lack of essential vitamins and minerals required in small amounts by the body for proper growth and development.
This data entry focuses on micronutrient deficiencies; our entries on undernourishment and obesity can be found at the links above.
In contrast to macronutrients (energy, protein and fat), micronutrients are vitamins and minerals which are consumed in small quantities, but are nonetheless essential for physical and mental development. Essential micronutrients include (but are not limited to): iron, zinc, calcium, iodine, vitamin A, B-vitamins, and vitamin C.
Micronutrient deficiencies form an important global health issue, with malnutrition affecting key development outcomes including poor physical and mental development in children, vulnerability or exacerbation of disease, mental retardation, blindness and general losses in productivity and potential. Unlike energy-protein undernourishment, the health impacts of micronutrient deficiency are not always acutely visible; it is therefore sometimes termed 'hidden hunger' (the two terms can be used interchangeably). The World Health Organization (WHO) estimate that more than two billion people suffer from micronutrient deficiency globally.
This entry explores global trends in key micronutrient deficiencies, potential health and development impacts, and progress in interventions to address vitamin and mineral deficiencies.
Although any individual can experience micronutrient deficiency, pregnant women and children are at greatest risk of developing deficiencies. This is not only as a result of low dietary intake, but also from higher physiological requirements; pregnancy and childhood development often increases demand for specific vitamins and minerals.
The nutritional status of pregnant women is not only relevant for her own health, but can also have important consequences for the development of her child. Monitoring and addressing micronutrient deficiencies in both pregnant women and early childhood years is therefore essential for optimal development and health within a given population.
Data on deficiency prevalence, impacts and intervention strategies are therefore gathered most frequently for these specific demographics. Much of the content which follows is therefore focused on (but not limited to) malnutrition in pregnant women and children under the age of five.
Anemia is a condition whereby an individual's blood lacks enough red blood cells (RBCs) to carry oxygen efficiently around the body. Anemia can result from a lack of iron or vitamin B12, although iron deficiency is the most common type.
Globally, anemia affects more people than any other health problem. Anemia has important implications for general productivity and development, reducing the work capacity of individuals by up to 20 percent. In more serious cases, anemia can lead to exacerbation of disease and illness. The World Health Organization estimate that 20 percent of maternal deaths are attributed to anemia alone.1
In the chart below we see the prevalence of anemia in pregnant women. Globally, around 40% of pregnant women are anemic.
The prevalence of anemia in pregnant women is typically lower in higher-income regions, being lowest in North America, and Europe & Central Asia. Rates are particularly high across South Asia and Sub-Saharan Africa; in some countries reaching over 60%.
In the chart below we see the prevalence of anemia in women of reproductive age (here defined as women between the ages of 15-49).
In the chart below we see the prevalence of anemia in children under the age of five.
Globally, around 42% of children have anemia.
Rates are lowest in higher-income regions of North America (9%), Europe & Central Asia (22%), and East Asia & the Pacific (26%). Rates are high across South Asia and Sub-Saharan Africa, with 55% and 60% of children being anemic, respectively.
Vitamin-A deficiency (VAD) is the leading cause of preventable blindess in children--manifesting in a milder form as night blindness, and progressing to permanent blindness in stronger cases. VAD also serves to exacerbate serious disease and illness, leading to increased rates of maternal and childhood mortality.
In the map below we see the prevalence of vitamin-A deficiency in pregnant women over the period from 1995 to 2005. Data collection on micronutrient deficiencies are often sporadic and less consistent than indicators of energy-protein malnutrition; time-series data for most countries is therefore unavailable. Note that countries with a gross domestic product (GDP) per capita greater than US$15,000 in 2005 are considered to be free from vitamin-A deficiency as a public health problem and are therefore excluded.
Prevalence rates are typically highest across Africa and Asia. Across North Africa, the Middle East and Central/East Asia, between 20 and 25 percent of pregnant women were vitamin-A deficient. Most countries across Sub-Saharan Africa and South Asia had slightly lower rates between 15 and 20 percent.
By 2005 the prevalence across Central Europe and Latin America was very low, with only a few percent of pregnant women considered to be deficient.
Vitamin-A deficiency can, in some cases, result in visual impairment or blindness. In moderate form, this is limited to night blindness, however in severe cases this can become permanent.
In the map below we see the prevalence of night blindness in pregnant women over the period 1995-2005. If we compare the incidence of night blindness to vitamin-A deficiency (in the previous section), we see that not all cases of deficiency result in night blindness.
The prevalence for night blindness for most countries is less than 5 percent. However, several countries across Sub-Saharan Africa and South Asia record higher rates between 5-20 percent. Ethiopia has the highest recorded rate of night blindness, occurring in just over one-in-five pregnant women.
In the map below we see the prevalence of vitamin-A deficiency in children under the age of 5, over the period from 1995 to 2005.
Prevalence rates are typically highest across Sub-Saharan Africa and South Asia, often reaching up to 60-70 percent. The highest prevalence occurs in Kenya, where almost 85 percent of children suffer from vitamin-A deficiency.
By 2005 the prevalence across Central Europe and Latin America was lower than in Africa and Asia, with rates of deficiency typically between 5-20 percent of children.
In the map below we see the prevalence of night blindness in children younger than 5 years old over the period 1995-2005. If we compare the incidence of night blindness to vitamin-A deficiency (in the previous section), we see that most cases of deficiency do not result in night blindness in children.
For most countries, less than 1 percent of children suffer from night blindness. In the most extreme case- Sudan- this rate was 8.5 percent over this period. This is an order of magnitude lower than the most extreme example of vitamin-A deficiency.
Globally, zinc deficiency is very common — particularly in lower-income countries where diets are cereal-dominant and typically lower in protein. Zinc deficiency can be prevalent in men, women and children (as opposed to anemia, which is much more common in women).
Zinc deficiency can have a number of negative health consequences, affecting the central nervous, gastrointestinal, immune, epidermal, reproductive, and skeletal systems.2 Zinc is an essential nutrient for growth and recovery; deficiencies can therefore stunt growth; increase susceptibility to disease and infection; increase recovery time, or in some cases, impair recovery; reduce mental capacity; and increase the prevalence of maternal, neonatal and child complications. 3 Higher morbidity and mortality in mothers and newborns is associated with high prevalence of zinc deficiency.4
In the chart below we see the prevalence of zinc deficiency across the total population (not exclusively women or children) from 1990-2005. Overall, we see that changes in rates of zinc deficiency have been relatively static over this period. Most high-income countries, especially across Europe, North America, Oceania and Central Asia have incidences of zinc deficiency below 5-10 percent of the total population.
The prevalence of zinc deficiency across Sub-Saharan Africa and South Asia is higher, and variable between 15 to 50 percent. The highest prevalence in 2005 was the Democratic Republic of Congo at 54 percent.
Since there are a range of micronutrient deficiencies and nutritional outcomes we can measure, it is difficult to distill the severity of micro-malnutrition into a single measure. One metric which has been developed to give an indication of the severity of this is the Global Hidden Hunger Index (GHHI). Note that the terms 'hidden hunger' and 'micronutrient deficiency' are often used interchangeably. The GHHI is most commonly used to assess the nutritional status of pre-school children (under the age of five).
The GHHI is calculated as the average of three nutritional indicators in pre-school children: the prevalence of stunting (children who are too short for their age); the anemia; and vitamin-A deficiency. In the map below we see national GHHI values over the period 1999-2009.
Hidden Hunger is defined as 'alarming high' across several countries in Sub-Saharan Africa and South Asia. The remaining countries in these regions typically fall within the 'moderate-to-severe' range. The majority of countries across Latin America, North Africa, Central Europe and East Asia are defined as having 'mild' hidden hunger issues.
If micronutrient requirements cannot be met through dietary intake alone (for example if households do not have access to or cannot affordable the dietary diversity required to meet micronutrient requirements) there are three key additional strategies which can be used to address deficiencies. These are supplementation, food fortification and biofortification.5
- Supplementation: supplementation is the delivery of concentrated micronutrients in pill, powder or liquid form;
- Food fortification: fortification is a subset of food processing and involves the addition of small amounts of micronutrients to food products often commonly consumed by the general population (such as cereals, wheat flours and rice);
- Biofortification: the use of agronomic and plant-breeding approaches in agriculture to increase the concentration of particular micronutrients in staple food crops. The most well-known example is so-called 'golden rice', which is rice grown with high concentrations of vitamin-A.
As covered earlier in this entry, children under the age of 5 are typically the most vulnerable to vitamin-A deficiency. Many countries try to tackle this issue by delivering vitamin-A supplements to children, in the form of high-dose capsules several times per year.
In the map below we see the coverage rate of vitamin-A supplementation in children aged between 6-59 months. This is defined to be sufficient if a child receives at least two high-dose capsules per year. In 2014, we see that the coverage rate of supplementation across many countries in Sub-Saharan Africa and South Asia is very high--in many cases greater than 90 percent.
Although some countries still have very low rates of coverage, progress has been considerably over the last few decades. Since 1990, coverage rates in South Asia have nearly doubled, and since 2000, coverage in Sub-Saharan Africa has increased almost five-fold.
Iodine deficiency is the leading cause of preventable brain damage in childhood. Recognised as a driver in perinatal mortality, a leading cause of mental retardation (iodine deficiency can result in a mean IQ loss of 13.5 points in the population), and thyroid impairments, in the mid-1980s, the world committed to ending global iodine deficiency.6
Iodine deficiency results from dietary intakes low in iodine; this typically occurs within populations with soils low in iodine content (thereby hindering iodine concentrations in crops). Iodine deficiency is therefore hard to address simply through dietary diversification.
The global solution to addressing deficiency has been through Universal Salt Iodization (USI) programmes. Salt is used as a delivery device for iodine for several reasons: it is widely consumed and has little seasonal variation; salt is typically distributed from a few centralised production centres; it has little impact on taste or texture of foods; and it is inexpensive (USI is estimated to cost US$ 0.02-0.05 per person per year).7
Since the WHO and UNICEF recommended USI to address iodine deficiency, the world has made significant progress. More than 120 countries now have USI programmes, and it's estimated that 71 percent of households across the world have access to iodized salt.8 Many countries have eliminated iodine deficiency as a public health issue.
Iodine deficiency remains a public health issue in some countries (particularly those of lower incomes). In the map below we see the share of households consuming iodized salt from 1993-2013. Overall, we see that many countries (even those of low income) have achieved levels between 60-100 percent. However, access across a handful of countries remains very low--in 2010 for example, less than 10 percent of households in Sudan and Mauritania consumed iodized salt.
One impact of micronutrient deficiency is its potential to exacerbate existing disease and illnesses. In 2015, nearly 500,000 children died from diarrheal diseases (the third largest cause of child mortality). Diarrhea, especially in children, has important links to malnutrition. Malnutrition can serve to exacerbate the risk of mortality from diarrhea. Additionally, diarrhea affects the ability of children to retain and utilise nutrients properly--this means requirements for nutrient intake is higher than under normal circumstances.
Treating diarrheal disease is therefore a nutritional, as well as general health issue. The map below shows the share of children under the age of 5 who received diarrheal treatment in the form of oral rehydration salts (ORS packets or pre-packaged ORS fluids).
To ensure adequate micronutrient intake through dietary intake alone (with the use of fortified, processed foods), a diverse diet is required. Micronutrient-rich foods include fruit and vegetables, meat and dairy, pulses, seafood, nuts and seeds. In contrast, cereal, root and tuber commodities tend to be energy-dense but micronutrient-poor.
In the chart below we have plotted the hidden hunger index in children (on the y-axis) versus the share of dietary energy attained through the consumption of cereals, roots and tubers. Overall, we see that countries where the average diet is rich in micronutrient-poor cereals tend to have higher levels of micronutrient deficiency (here shown as hidden hunger in children).
In the chart below we have plotted the Hidden Hunger Index in pre-school children (on the y-axis) versus gross domestic product (GDP) per capita, measured in 2011 international-$ (on the x-axis). Overall, we see that countries with lower GDP per capita experience more severe deficiency and malnutrition issues in children. This is also true of deficiency measures, such as the prevalence of anemia in women of reproductive age.
Why is micronutrient deficiency more prominent at lower incomes? Since cereals tend to be less expensive than other food commodities, poorer households tend to have a more monotonous, energy-dense diet lacking in the dietary diversity required to meet micronutrient requirements.9 Richer households can instead afford to supplement staple food items with a diverse range of micronutrient-rich foods.
The dietary requirement for a given micronutrient is defined as the level which meets criteria for being adequate to minimise risk of nutrient deficit or excessive intake. These levels are typically derived based on biomarkers or signs and symptoms which are indicative of clinical disease or nutrient deficiency.
Nutrient requirements vary between individuals based on a range of factors, including age, sex, physical activity levels, and can be higher during periods of pregnancy, lactation, and disease. In individuals, specific requirement figures can be used based on their demographic profile. When assessing average requirements across groups or populations, requirements must be weighted based on the "Estimated Average Requirement" (EAR) of the individuals within the population. Distribution curves of intake and requirement can then be utilised to provide an estimate of the prevalence or risk of deficiency across the population.
World Development Indicators by the World Bank
- Data: Prevalence of anemia, vitamin-A deficiency, supplementation and diarrhea treament
- Geographical coverage: Global – by country and demographic group
- Time span: Variable data since 1985
- Available at: Online here.
World Health Organization Vitamin and Mineral Nutrition Information System (VMNIS)
- Data: Biomarkers of vitamin and mineral nutrition in populations
- Geographical coverage: Global – by country
- Time span: Currently under construction
- Available at: Online here.
International Food Policy Research Institute (IFPRI)
- Data: Various dimensions on nutrition and food security at national, household and community-level
- Geographical coverage: Primarily Africa and Asia – by country, and at household levels
- Available at: Online here.