UNICEF - Environmental determinants of undernutrition and micronutrient deficiencies in children

Environmental determinants of undernutrition and micronutrient deficiencies in children Executive summary © UNICEF/UN0885368/Meerzad Nutrition, particularly during the first 1,000 days of life – from conception to the child’s second birthday – is a core determinant of child survival, physical growth and development, present and future health and well-being, and learning and earning potential, with positive impacts into the next generation. Multiple factors determine children’s diets and nutrition globally. Growing evidence reinforces the role of the environment as a fundamental determinant of nutrition and other health-related outcomes. Environmental hazards – agents or conditions that exist in a person’s environment with the potential to cause harm – can be physical (e.g., heat, radiation, noise, climate and weather), chemical pollutants/ toxicants, and biological (bacteria, viruses, parasites, vectors). Water , sanitation and hygiene (WASH) is a well-known determinant of poor nutritional outcomes, linked to 10 per cent of cases of undernutrition. Beyond WASH, the effects of exposure to chemicals and other biological hazards on nutrition outcomes are under-recognized. This document highlights the influence of environmental hazards on childhood undernutrition and micronutrient deficiencies, with a focus on chemical and biological exposures. It supports integrating environmental health through a multisectoral approach to reduce the environmental determinants of undernutrition and micronutrient deficiencies. Health care workers can help advance this integration by screening for environmental exposures and providing guidance during child health visits, educating families on reducing exposure to environmental hazards during nutritional counselling, and championing healthier environments for all children.Introduction Under international norms, malnutrition is a violation of children’s rights (UNICEF, 2026a). The United Nations second Sustainable Development Goal ( SDG 2) aims to “end hunger , achieve food security and improved nutrition, and promote sustainable agriculture by 2030.” However , despite global efforts and progress, compounding drivers continue to impact the systems

second Sustainable Development Goal ( SDG 2) aims to “end hunger , achieve food security and improved nutrition, and promote sustainable agriculture by 2030.” However , despite global efforts and progress, compounding drivers continue to impact the systems needed to end childhood hunger and meet the global nutrition targets. Inequities, globalization, relentless urbanization and recent and evolving crises – including climate hazards, public health crises such as the COVID-19 pandemic, and armed conflicts – undermine the quality of children’s diets and care, disproportionately affecting children in lowand middle-income countries (LMICs). Increasingly, children face a triple burden of malnutrition, with the coexistence of undernutrition (stunting, wasting, and underweight), micronutrient deficiencies (‘hidden hunger’), and overweight and obesity, resulting in negative long-term outcomes for children that affect whole societies and nations. UNICEF’s nutrition strategy prioritizes the prevention of all forms of child malnutrition across the life cycle and supports the early detection and treatment of life-threatening malnutrition (UNICEF, 2020). This document focuses on undernutrition and micronutrient deficiencies. 2Childhood malnutrition is an imbalance (deficiency or excess) between the body’s nutrient requirements and the intake of energy, macronutrients, and/or micronutrients (World Health Organization, 2026). The clinical manifestations of malnutrition include undernutrition (wasting, stunting and underweight), micronutrient deficiencies and overnutrition (overweight and obesity). Wasting Acute malnutrition indicated by low weight for height. It is often indicative of recent, severe weight loss, but can also persist for a long time. Worldwide, 42.8 million children under 5 have wasting. Stunting Chronic malnutrition is indicated by low height for age (linear growth retardation). Child’s height for age exceeds two standard deviations below WHO child growth standards. Worldwide, 150.2 million children are stunted. Underweight Low weight for age. The underweight child may be wasted, stunted or both.

Stunting Chronic malnutrition is indicated by low height for age (linear growth retardation). Child’s height for age exceeds two standard deviations below WHO child growth standards. Worldwide, 150.2 million children are stunted. Underweight Low weight for age. The underweight child may be wasted, stunted or both. Micronutrient deficiencies (also known as ‘hidden hunger’) Lack of vitamins and minerals that are essential for bodily functions, growth and development. Depending on the micronutrient, these deficiencies in children are associated with serious adverse health outcomes, including impaired physical and cognitive development, blindness, anaemia, immune deficiencies, increased susceptibility to infections and mortality, among others. Table 1. World Health Organization (WHO) definitions for childhood undernutrition and micronutrient deficiencies © UNICEF/UN0339430/Dejongh Overview of childhood undernutrition and micronutrient deficiencies

Source: WHO

3Global child stunting and wasting rates have declined during the last decade, with an estimated prevalence of 23.2 per cent and 6.6 per cent respectively. Despite these advancements, according to the Joint Malnutrition Estimates, only 28 per cent of the countries assessed in 2025 are on track to halve the number of children affected by stunting by 2030. After a decade of declines in stunting, estimates now show a worrying halt to progress. Children under 5 years are the most vulnerable to undernutrition, particularly those aged under 2 living in LMICs (Mao et al., 2024). Undernutrition is associated with up to 45 per cent of deaths in children under 5, mainly through synergistic effects between childhood wasting and infectious diseases such as diarrhoea and pneumonia (Carvalho et al., 2025; World Health Organization, 2026). Children with concurrent wasting and stunting have the highest risk of death; and severe underweight and combined moderate wasting/ stunting are associated with a mortality relative risk of

and pneumonia (Carvalho et al., 2025; World Health Organization, 2026). Children with concurrent wasting and stunting have the highest risk of death; and severe underweight and combined moderate wasting/ stunting are associated with a mortality relative risk of 4.8 by age 24 months (Yue et al., 2022). Child growth failure is the second leading risk factor associated with health burden in children under 5 years, and it is associated with 880,000 deaths (18.8 per cent of all under 5 deaths) and an estimate of 79.4 million under 5 disability-adjusted life years (DALYs) (GBD 2023 Child Growth Failure Collaborators, 2026). Globally, approximately 40 per cent (269 million) of children aged 6 months to 59 months have anaemia, and 372 million are deficient in at least one of three core micronutrients (iron, zinc and vitamin A). Approximately 37 per cent of pregnant women have anaemia (World Health Organization, 2025a). The most prevalent micronutrient deficiencies in children are iron, iodine, vitamin A, zinc and folate (Bailey et al., 2015). True population-based national data on micronutrient deficiencies are available from very few countries; therefore, global burden of disease estimates rely heavily on modelled data. According to estimates, in 2019, there were 435 million prevalent cases of childhood nutritional deficiencies globally, with 52 million new incident cases, 105,000 deaths, and 26 million DALYs. The burden remains disproportionately concentrated in low-sociodemographic index (SDI) and low-middle-SDI countries (Liu et al., 2024). Burden of undernutrition and micronutrient deficiencies in children Source: UNICEF, WHO, World Bank Group Joint Malnutrition Estimates, 2025 edition. Figure 1. Global overview, prevalence and number (millions) affected 4“Child malnutrition and climate

Burden of undernutrition and micronutrient deficiencies in children Source: UNICEF, WHO, World Bank Group Joint Malnutrition Estimates, 2025 edition. Figure 1. Global overview, prevalence and number (millions) affected 4“Child malnutrition and climate change are two of the greatest threats facing nations today. They converge geographically, share common systemic and societal drivers, and exacerbate one another . Millions of families are struggling to meet children’s nutritional needs under the strain of climate change, while greenhouse gas emissions from food systems remain one of the main drivers of the climate crisis.” – UNICEF (n.d.) © UNICEF/UNI806119/Franco Source: Introduction to UNICEF’s Child Nutrition and Climate Change framework, published on their technical knowledge portal, Knowledge @ UNICEF. Clinical consequences of childhood undernutrition and micronutrient deficiencies Undernutrition impairs both innate and adaptive immunity, increasing vulnerability to infections and the severity of illness (Ibrahim et al., 2017; Bourke et al., 2019). Protein and micronutrient deficiencies disrupt haematopoietic and lymphoid organs and are associated with malnutrition-related changes in the gut microbiome that can further compromise immune defence mechanisms (Ibrahim et al., 2017). Stunting and wasting are linked to impaired cognitive and motor development (Ali et al., 2025). Severe acute malnutrition is associated with significantly lower cognitive and motor scores than those of wellnourished peers. Stunting before age 2 is a significant predictor of impaired cognitive development and reduced educational attainment in later childhood and adolescence and is consistently correlated with long-term consequences for human capital, workforce productivity and wage potential, particularly in LMICs (Akseer et al., 2022; McGovern et al., 2017). Early-life undernutrition, especially during the critical periods of in utero and early childhood growth, is associated with an increased risk of

productivity and wage potential, particularly in LMICs (Akseer et al., 2022; McGovern et al., 2017). Early-life undernutrition, especially during the critical periods of in utero and early childhood growth, is associated with an increased risk of non-communicable diseases (NCDs) in adulthood, including cardiovascular disease, type 2 diabetes, and obesity (Grey et al., 2021). This risk for NCDs is magnified when children, who are chronically underweight and/or stunted early in life, later experience rapid weight gain through transition to nutritional excess through energy-dense and/ or obesogenic diets that result in central adiposity and metabolic syndrome, as nutritional deficiencies constrain metabolically critical tissues early in development (Wells et al., 2020). The effects of childhood micronutrient deficiencies on health depend on the type of micronutrient (Table 2) and may persist into adulthood and across generations when maternal deficiencies affect fetal programming (Victora et al., 2021). © UNICEF/UN0304027/Dejongh 5Table 2. Clinical consequences of the most common prenatal and childhood micronutrient deficiencies Micronutrient Clinical consequences linked to deficiency Iron • Developmental and cognitive deficits, attention, learning and academic problems; poor pregnancy outcomes (including low birth weight, pre-eclampsia, preterm delivery and maternal mortality), and immune dysfunction Vitamin A • Xerophthalmia (a leading cause of preventable blindness in children); poor growth and development; increased risk of death from infectious diseases, particularly diarrhoeal, respiratory and measles (Song et al., 2023) Zinc • Impaired growth and weight gain; neuronal abnormalities; iron deficiency anaemia; compromised immunity; increased risk of pollutant hazards through altered response to oxidative stress; risk for cardiovascular diseases Iodine • Pregnancy loss and stillbirth; congenital anomalies; congenital hypothyroidism; perinatal infant mortality; impaired mental function and cognitive disability; delayed physical development;

immunity; increased risk of pollutant hazards through altered response to oxidative stress; risk for cardiovascular diseases Iodine • Pregnancy loss and stillbirth; congenital anomalies; congenital hypothyroidism; perinatal infant mortality; impaired mental function and cognitive disability; delayed physical development; reduced somatic growth; thyroid gland enlargement (goitre) (Zimmermann, 2012; Taylor et al., 2014; Walker et al., 2007) Folate (vitamin B9) • Periconceptional and prenatal folate deficiency are associated with increased risk of neural tube defects, impaired fetal growth and premature birth The determinants of undernutrition and micronutrient deficiencies in children The aetiology of malnutrition is multifactorial, arising from the complex interplay among individual characteristics and environmental and socioeconomic determinants, operating through diverse pathways. These determinants co-occur and interact, amplifying effects across generations. To achieve SDG 2, multiple system actions are needed to promote and support the determinants of good nutrition across the life cycle, from preconception through adolescence. The UNICEF Conceptual Framework on Maternal and Child Nutrition (2020) frames childhood nutrition as resulting from the interaction of preconceptual, prenatal and postnatal determinants, including diets and care as the immediate determinants. Good diets are driven by adequate food and care (feeding and dietary practices). The underlying determinants include the food, practices and services available in households and communities to support good nutrition, while enabling determinants include the resources, norms and governance that facilitate it. © UNICEF/UN0304027/Dejongh 6The environment as a key determinant of good nutrition Chemical exposures, undernutrition, and micronutrient deficiencies Pollution is conceptualized as the “presence or introduction into the environment of substances or energy that cause adverse effects on human health, the environment or living organisms; or that exceed the quality or quantity criteria established for certain environmental media” (United Nations

micronutrient deficiencies Pollution is conceptualized as the “presence or introduction into the environment of substances or energy that cause adverse effects on human health, the environment or living organisms; or that exceed the quality or quantity criteria established for certain environmental media” (United Nations Children’s Fund, n.d.). Environmental degradation drives human degradation. Literature describes a ‘triple planetary crisis’ (climate change, biodiversity loss and pollution) that is affecting human health and well-being, threatening ecosystems, altering socioeconomic stability and undermining food and water safety and security. Evidence on human populations, and animal and cellular models show that pollution can drive childhood undernutrition and micronutrient deficiencies through multiple pathways, including repeated diarrhoea, helminth infection, and environmental enteric dysfunction in the case of inadequate WASH, and direct toxicity and impaired nutrient absorption and utilization, in the case of chemical and other biological hazards. Physical environmental determinants also operate upstream on the agriculture/food system itself – reducing food quantity, degrading food quality/nutrient density, and disrupting access and affordability – which increases food insecurity and, in turn, undernutrition (Figure 1). Over 80,000 chemicals (3,000 produced in high volumes) are found in the water , food, air , soil and built environments. The same food that should nourish and provide essential nutrients for optimal health and development can also expose people to contaminants linked to undernutrition. Chemical toxicants can enter children’s diets through the food chain by three main pathways: 1) Contaminating water , livestock, fish and other seafood 2) Agricultural practices (e.g., the use of pesticides and fertilizers, polluted soil and irrigation water , and inadequate harvesting practices) 3) Food processing and packaging. The relationship between the environment and nutrition in children is bidirectional; healthy environments drive good nutrition, and children who are well nourished have a decreased risk of adverse outcomes from pollution. Research suggests

and fertilizers, polluted soil and irrigation water , and inadequate harvesting practices) 3) Food processing and packaging. The relationship between the environment and nutrition in children is bidirectional; healthy environments drive good nutrition, and children who are well nourished have a decreased risk of adverse outcomes from pollution. Research suggests that diets rich in anti-inflammatory bioactive food components (phytochemicals, polyphenols, and antioxidant nutrients) may modulate and reduce the toxicity and disease risks associated with certain environmental pollutants, with the most consistent evidence from studies in adults supporting whole dietary patterns rather than isolated antioxidant supplements (Hoffman & Hennig, 2017). Conversely, nutritional deficiencies can amplify vulnerability to toxicant-related health effects with data suggesting mechanisms that include enhanced absorption via shared transport pathways, impaired detoxification capacity, altered pharmacokinetics (Ngcobo, 2025), and increased susceptibility to oxidative stress and inflammation (Palmer et al., 2024). Furthermore, nutrient deficiencies and chemical pollutants can synergize to amplify adverse health outcomes (e.g., anaemia/micronutrient deficiencies and lead absorption). Quantifying the burden of childhood undernutrition and micronutrient deficiencies attributable to environmental exposures is challenging. The potential effects of most chemicals already introduced in our environment on childhood nutrition have not been studied and the evidence on combined environmental exposures and child undernutrition is sparse, with much mechanistic work done on animal and in vitro models. Nevertheless, some chemicals and groups of chemicals have been studied and identified as health and nutrition risks, especially for children. Data have shown that some of these exposures can adversely impact several distinct outcomes: growth, nutrition, neurodevelopment and risk for later cardiometabolic disease, among others (Potiris et al., 2025; Romano et al., 2026). 7Metals Prenatal and early-life exposure to metals (e.g., lead,

impact several distinct outcomes: growth, nutrition, neurodevelopment and risk for later cardiometabolic disease, among others (Potiris et al., 2025; Romano et al., 2026). 7Metals Prenatal and early-life exposure to metals (e.g., lead, cadmium, mercury, arsenic) has been associated with impaired growth, stunting and anaemia (Bede-Ojimadu et al., 2025). Metals are linked to disruption of nutrient absorption and metabolism; direct toxicity to organ systems involved in growth and haematopoiesis; synergism with undernutrition (e.g., dietary deficiencies of calcium, zinc and iron enhance neurodevelopmental impacts of lead); and increased metabolic demands. Cadmium, lead and mercury are common air pollutants (World Health Organization, n.d.). The coexistence of high blood lead or cadmium levels and nutrient deficiencies has been linked to subclinical damage to haematopoietic, renal and nervous tissues (Bharatraj et al., 2018). On the other hand, nutritional deficiencies can alter the absorption, distribution and retention of various metals. For example, iron deficiency, with or without anaemia, enhances lead absorption Air pollutants Air pollutants – specifically particulate matter with a diameter of 2.5 micrometres or less (PM 2.5), and to a lesser degree, nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO) – are associated with impaired fetal and early childhood growth, stunting and anaemia (Brumberg et al., 2021; Khezri et al., 2025; Pun et al., 2021; Pambianchi et al., 2022; Jin et al., 2025). Proposed mechanisms include systemic inflammation supported by human meta-analytic data showing elevated CRP1 and TNF-α2 with gaseous pollutant exposure (Xu et al., 2022), and alterations

al., 2025). Proposed mechanisms include systemic inflammation supported by human meta-analytic data showing elevated CRP1 and TNF-α2 with gaseous pollutant exposure (Xu et al., 2022), and alterations in nutrient metabolism, based largely on in vitro and animal evidence (Sangphech et al., 2026). Household air pollution (HAP) is associated with several adverse health outcomes. In 2020, approximately one third of the global population used solid fuels (e.g., firewood and charcoal) for cooking (Woolley et al., 2022; GBD, 2025; Stoner et al., 2021). The observational association between HAP from incomplete combustion and childhood stunting is well documented and consistent across settings. However , the causal pathway appears complex, and clean fuel interventions alone have not yet demonstrated reductions in stunting in randomized controlled trials (Checkley et al., 2024), suggesting that HAP reduction must be part of broader integrated multisectoral approaches that invest in community infrastructure. Children whose parents/caretakers smoke tobacco face higher dose-dependent risks of growth stunting (World through a common intestinal transporter . This is concerning because lead is responsible for a significant global disease burden and, even at low exposure levels, can cause lifelong and irreversible adverse neurodevelopmental outcomes (Disalvo et al., 2025). Lead remains a global public health threat, with one third (800 million) of children having blood lead levels at or above 5 µg/dL (UNICEF and Pure Earth, 2020). Health Organization, 2025b). Maternal smoking and exposure to second-hand smoke are strongly linked to preterm birth, congenital anomalies, restricted fetal growth, low birth weight and an increased risk for chronic diseases later in life, especially if the child has growth stunted by age two (Al-Mughathwai et al., 2025). Quitting smoking during pregnancy improves child growth outcomes. Second-hand

fetal growth, low birth weight and an increased risk for chronic diseases later in life, especially if the child has growth stunted by age two (Al-Mughathwai et al., 2025). Quitting smoking during pregnancy improves child growth outcomes. Second-hand tobacco smoke exposure after birth is associated with neurodevelopmental and behavioural problems and increases the risk and severity of respiratory infections and developmental problems; and has also been associated with reduced height for age and stunting in some populations (World Health Organization, 2025b). 1 C-reactive protein is released by the liver into the blood in response to an inflammation from an infection, injury, or long-term disease 2 Tumour necrosis factor is a chemical messenger produced by the immune system that induces inflammation © UNICEF/UN0920912/Agyemang© UNICEF/UNI724369/Phiennachit 8Endocrine-disrupting chemicals Endocrine-disrupting chemicals (EDCs) are synthetic and natural substances that interfere with any aspect of hormone function (synthesis, transport, metabolism and excretion), leading to a broad spectrum of adverse health effects, particularly on growth, pubertal development and metabolism. Among other sources, children are commonly exposed to mixtures of EDCs through water and food contamination. For example, perand polyfluoroalkyl substances (PFAS), phthalates and bisphenol A are commonly found in food contact materials (e.g., packaging, storage) and are highly prevalent in ultra-processed foods. Urinary phthalate metabolites have been inversely associated with serum folate concentrations in US children aged 6–18 years, but the evidence is cross-sectional and no link to clinical folate deficiency has been established (He et al., 2024). Even though EDCs have not been a focus of undernutrition literature, exposure to these chemicals during pregnancy has been associated Pesticides Children can be exposed to pesticides prenatally (through the placenta); through contaminated food

(He et al., 2024). Even though EDCs have not been a focus of undernutrition literature, exposure to these chemicals during pregnancy has been associated Pesticides Children can be exposed to pesticides prenatally (through the placenta); through contaminated food and water; through chemicals stored in the home or dumped in public areas; if they live in or near agricultural areas; and occupationally. Globally, 84 million children are engaged in agricultural work, with pesticide levels consistently higher than in the general population (ILO & UNICEF, 2026b). A higher risk of exposure is also observed among families living near agricultural land and among those with improper pesticide management. Despite the Codex Alimentarius, which sets maximum pesticide residue limits adopted by most countries, children are exposed to pesticides through toxic residues in the food they eat (UNICEF, 2018). Overreliance on pesticides in agriculture to reduce hunger undermines several SDGs. Pesticides are a critical threat to children’s health, affecting their developing immune, endocrine and nervous systems. Exposure to pesticide residues among women and children in farm settings has been linked to low vitamin and mineral levels, acetylcholine inhibition, and altered oxidative stress parameters (Medithi et al., 2022); as well as to oxidative stress, oxidative DNA damage, and inflammation (AguilarBañuelos et al., 2025). Separate studies found lower haemoglobin and lymphocyte counts and elevated inflammation indices in the highest-exposure with reduced birth weight and impaired fetal/infant growth (Svensson et al., 2021). Direct evidence linking exposure to EDCs and undernutrition using WHOdefined stunting and wasting endpoints is limited. community and lower levels of vitamin D. However , most evidence comes from occupational/agricultural exposure settings and cross-sectional studies, and animal models. Direct evidence linking dietary pesticide residue levels or household use at typical consumer exposure to clinically significant micronutrient

defined stunting and wasting endpoints is limited. community and lower levels of vitamin D. However , most evidence comes from occupational/agricultural exposure settings and cross-sectional studies, and animal models. Direct evidence linking dietary pesticide residue levels or household use at typical consumer exposure to clinically significant micronutrient deficiencies in children remains limited. Direct evidence linking pesticide exposure to stunting or wasting is limited. On the other hand, malnourished children (particularly those with oedematous undernutrition) may be more vulnerable to pesticide toxicity in part due to severe depletion of antioxidant nutrients. © UNICEF/UNI974767/Izquierdo © UNICEF/UNI82747/Vink 9Biological exposures, undernutrition and micronutrient deficiencies WASH Inadequate WASH results in 1.4 million people dying yearly (395,000 children under the age of 5, in 2019), mostly in LMICs (Wolf et al., 2023). WASH-related biological exposures can lead to acute and chronic diarrhoeal diseases, enteric fever and parasitic infections. Subclinical enteric pathogens and enteroaggregative Escherichia coli infections are more prevalent among children with malnutrition (Lima et al., 2017). Parasitic infections (malaria and helminths) are consistently associated with anaemia and stunting (Hhera et al., 2025). Environmental enteric dysfunction (EED) – a subclinical inflammatory disorder of the small intestine caused by chronic exposure to faecal contaminated water , food, soil and fomites and recurrent subclinical enteric infections from multiple transmission routes – is characterized by increased intestinal permeability, intestinal and systemic inflammation, malabsorption, alterations in growth-related hormones, and dysbiosis of the intestinal microbiota (Owino et al., 2016; Lauer et al., 2020). EED has been hypothesized as a major contributor to childhood undernutrition, including

intestinal and systemic inflammation, malabsorption, alterations in growth-related hormones, and dysbiosis of the intestinal microbiota (Owino et al., 2016; Lauer et al., 2020). EED has been hypothesized as a major contributor to childhood undernutrition, including stunting, and is highly prevalent in environments with heavy faecal contamination and poor sanitation (Gizaw et al., 2022). Low-cost household-level WASH interventions tested in three landmark trials did not improve child linear growth, but comprehensive or intensive WASH approaches – such as community-level sanitation, sewered systems and safely managed water services, particularly when integrated with nutrition – have shown benefits by reducing the risk of diarrhoeal disease and child mortality (Gizaw et al., 2022). © UNICEF/UN0150187/Dejongh Mycotoxins Exposure to naturally occurring mycotoxins in the food chain is prevalent, and infants are at higher risk (Etzel, 2014). Mycotoxins are chemically stable and can survive food processing (World Health Organization, 2023b). Early-life exposure is associated with low birth weight, stunting, and immune suppression (Watson et al., 2017; Vilcins et al., 2018). A systematic review found that uncertainty remains as to whether dietary mycotoxin exposure directly affects child growth and immunity, grading the overall evidence as very low quality due to inconsistencies across studies, while not ruling out an association with aflatoxin and fumonisin (Hadush et al., 2020); a subsequent metaanalysis of prospective cohorts found aflatoxin B 1 exposure associated with underw