Hidden hunger, also known as micronutrient deficiencies, afflicts more than 2 billion individuals, or one in three people, globally (FAO 2013). Its effects can be devastating, leading to mental impairment, poor health, low productivity, and even death. Its adverse effects on child health and survival are particularly acute, especially within the first 1,000 days of a child’s life, from conception to the age of two, resulting in serious physical and cognitive consequences.

Even mild to moderate deficiencies can affect a person’s well-being and development. In addition to affecting human health, hidden hunger can curtail socioeconomic development, particularly in low and middle income countries.

A Different Kind of Hunger

Hidden hunger is a form of undernutrition that occurs when intake and absorption of vitamins and minerals (such as zinc, iodine, and iron) are too low to sustain good health and development (Box 3.1).

Factors that contribute to micronutrient deficiencies include poor diet, increased micronutrient needs during certain life stages, such as pregnancy and lactation, and health problems such as diseases, infections, or parasites.

While clinical signs of hidden hunger, such as night blindness due to vitamin A deficiency and goiter from inadequate iodine intake, become visible once deficiencies become severe, the health and development of a much larger share of the population is affected by less obvious “invisible” effects. That is why micronutrient deficiencies are often referred to as hidden hunger.

More than 2 billion people worldwide suffer from hidden hunger, more than double the 805 million people who do not have enough calories to eat (FAO, IFAD, and WFP 2014). Much of Africa south of the Sahara and the South Asian subcontinent are hotspots where the prevalence of hidden hunger is high (Figure 3.1 [right]). The rates are relatively low in Latin America and the Caribbean where diets rely less on single staples and are more affected by widespread deployment of micronutrient interventions, nutrition education, and basic health services (Weisstaub and Araya 2008). Although a larger proportion of the burden of hidden hunger is found in the developing world, micronutrient deficiency, particularly iron and iodine deficiency, is also widespread in the developed world (Figures 3.1 [right] and 3.2 [below]).

The nature of the malnutrition burden facing the world is increasingly complex. Developing countries are moving from traditional diets based on minimally processed foods to highly processed, energy-dense, micronutrient-poor foods and drinks, which lead to obesity and diet-related chronic diseases. With this nutrition transition, many developing countries face a phenomenon known as the “triple burden” of malnutrition—undernourishment, micronutrient deficiencies, and obesity (Pinstrup-Andersen 2007). In higher income, more urbanized countries, hidden hunger can coexist with overweight/obesity when a person consumes too much dietary energy from macronutrients such as fats and carbohydrates (Guralnik et al. 2004). While it may seem paradoxical, an obese child can suffer from hidden hunger.

Micronutrient deficiencies cause an estimated 1.1 million of the 3.1 million child deaths that occur each year as a result of undernutrition (Black et al. 2013; Black et al. 2008). Vitamin A and zinc deficiencies adversely affect child health and survival by weakening the immune system. Lack of zinc impairs growth and can lead to stunting in children. Iodine and iron deficits prevent children from reaching their physical and intellectual potential (Allen 2001).

Women and children have greater needs for micronutrients (Darnton-Hill et al. 2005). The nutritional status of women around the time of conception and during pregnancy has long-term effects for fetal growth and development. Nearly 18 million babies are born with brain damage due to iodine deficiency each year. Severe anemia contributes to the death of 50,000 women in childbirth each year. In addition, iron deficiency saps the energy of 40 percent of women in the developing world (UNSCN 2005; Micronutrient Initiative 2014). Interventions to fight hidden hunger and improve nutrition outcomes generally focus on women, infants, and young children. By targeting these populations, interventions achieve high rates of return by improving health, nutritional status, and cognition later in life (Hoddinott et al. 2013).

The most commonly recognized micronutrient deficiencies across all ages, in order of prevalence, are caused by a lack of iodine, iron, and zinc (Table 3.1, right). Less common, but significant from a public health standpoint, is vitamin A deficiency, with an estimated 190 million pre-school children and 19 million pregnant women affected (WHO 2009). Low intakes of other essential micronutrients, such as calcium, vitamin D, and B vitamins, such as folate are also common (Allen et al. 2006). Although pregnant women, children, and adolescents are often cited as populations affected the most by hidden hunger, it impairs the health of people throughout the life cycle (Figure 3.3, right).

It is difficult to describe the magnitude of deficits for most micronutrients. For many micronutrient deficits, prevalence data are scarce. Scientists have not reached a consensus on standard recommended intakes for many of the 19 micronutrients that directly influence physical and mental development and the immune system (Biesalski 2013). Furthermore, for many micronutrients, the relationship between intake and utilization is not well understood.

Obtaining accurate data is a challenge. Time lags, data gaps, and lack of disaggregation are common problems. Often proxies for common examples of hidden hunger are imperfect. For example, anemia is used as a proxy for iron deficiency, although only half of all anemia is caused by iron deficiency (de Benoist et al. 2008). Typical physical measurements of hunger, such as stunting (low height for one’s age), wasting (low weight for one’s height), and underweight, may capture micronutrient deficiencies in affected populations, but are inadequate proxies, because the deficiencies are seldom the only factors involved. Exact measurements via blood samples, and also by specific diagnoses, such as night blindness, beriberi, and scurvy, are more reliable ways to determine micronutrient deficiencies. Many important micronutrients lack prevalence data, because related biomarkers have not yet been identified for a nutrient deficit. As long as these gaps in data persist, it will be difficult to describe the full contours of hidden hunger.

Poor diet is a common source of hidden hunger. Diets based mostly on staple crops, such as maize, wheat, rice, and cassava, which provide a large share of energy but relatively low amounts of essential vitamins and minerals, frequently result in hidden hunger.

What people eat depends on many factors, including relative prices (Box 3.2) and preferences shaped by culture; peer pressure; and geographical, environmental, and seasonal factors. Victims of hidden hunger may not understand the importance of a balanced, nutritious diet. Nor may they be able to afford or access a wide range of nutritious foods such as animal-source foods (meat, eggs, fish, and dairy), fruits, or vegetables, especially in developing countries. In non-emergency situations, poverty is a major factor that limits access to adequate nutritious foods.

When food prices rise, consumers tend to continue to eat staple foods while cutting their intake of non-staple foods that tend to be richer in micronutrients (Bouis, Eozenou, and Rahman 2011).

Another source of micronutrient deficiencies is impaired absorption or use of nutrients. Absorption may be impaired by infection or a parasite that can also lead to the loss of or increased need for many micronutrients. Infections and parasites can spread easily in unhealthy environments with poor water, sanitation, and hygiene conditions. Unsafe food handling and feeding practices can further exacerbate nutrient losses.

Diet also affects absorption. Fat-soluble vitamins such as vitamin A are best absorbed when consumed with dietary fat, while consumption of some compounds such as tannins or phytates can inhibit iron absorption. Alcohol consumption can interfere with the absorption of micronutrients.

Vitamin and mineral deficiencies impose a significant burden on the affected persons and societies, both in terms of health costs and negative impacts in lost human capital and reduced economic productivity.

Hidden hunger impairs physical growth and learning, limits productivity, and ultimately perpetuates poverty (Figure 3.4) in a continuous cycle. Countries where a large share of the population is affected by vitamin and mineral deficiencies cannot realize their economic potential (Stein 2013; Stein and Qaim 2007). Poor people disproportionately suffer from micronutrient deficiencies, and bear the long-term negative effects that constrain socioeconomic development (Darnton-Hill et al. 2005).

The economic costs of all forms of micronutrient deficiency can be considerable, cutting gross domestic product by 0.7–2 percent in most developing countries (Micronutrient Initiative and UNICEF 2004). For example, it is estimated that India sustains a 1 percent loss in GDP and Afghanistan a 2.3 percent loss. Global losses in economic productivity due to macronutrient and micronutrient deficiencies reach more than 2 to 3 percent of GDP (World Bank 2006) at a global cost of US$1.4 to 2.1 trillion per year (FAO 2013).

On the other hand, the return on investment in nutrition can be high. Copenhagen Consensus Expert Panels consistently find nutrition interventions cost-effective (Copenhagen Consensus 2004, 2008, 2012). In 2008, the panel ranked supplements for children (vitamin A and zinc), fortification (iron and iodine), and biofortification among the top five best investments for economic development.

For example, estimates for salt iodization suggest that every dollar invested generates up to US$81 in benefits (Hoddinott, Rosegrant, and Torero 2012).