Anemia Prevalence, Causes, and Consequences

What is anemia?

Anemia is defined as a low level of hemoglobin in the blood, as evidenced by fewer numbers of functioning red blood cells. Hemoglobin in red blood cells is an oxygen-carrying protein that binds oxygen through its iron component. Hemoglobin transports oxygen to most cells in the body for the generation of energy. When hemoglobin levels are low, less oxygen reaches the cells to support the body's activities. The heart and lungs also must work harder to compensate for the blood's low capacity to carry oxygen. Because of oxygen's role in generating energy in the body and hemoglobin's role in transporting oxygen, one of the first symptoms of anemia is feeling tired. Because the heart has to work harder to get blood and oxygen to the tissues, anemia, particularly severe anemia, can result in cardiac arrest. Click here for World Health Organization (WHO) cutoffs of hemoglobin that define all, mild, moderate, and severe anemia.

Who does anemia affect?

Globally, anemia is prevalent in most developing countries and considered of public health significance. Click here for the WHO definitions for the levels of public health significance based on anemia prevalence.

The WHO (2008) has estimated the worldwide prevalence of anemia by regions and population groups. Women and young children are most vulnerable to anemia. The proportion of women and children is highest in the Africa region where 57% of pregnant women (17 million), 48% of non-pregnant women (70 million), and 68% of preschool children (84 million) are anemic. While the proportion of people with anemia is lower in Southeast Asia, the number of people with anemia are higher than in the Africa region. In Southeast Asia, 48% of pregnant women (18 million), 46% of non-pregnant women (182 million), and 66% of preschool children (115 million) suffer from anemia. A pictoral representation of the prevalence of anemia is shown in the map below.


Click here for the WHO global estimates of anemia prevalence. Click here for the WHO estimates of anemia prevalence by vulnerable group and region.

What are the causes of anemia?

There are three main categories of the causes of anemia: 1) poor, insufficient, or abnormal red blood cell production; 2) excessive red blood cell destruction; and 3) excessive red blood cell loss. In developed countries, iron deficiency is the major cause of anemia and results in insufficient red blood cell production. In some individuals, infections such as peptic ulcers may cause blood loss and anemia. In developing countries, iron deficiency affects all vulnerable groups. Malaria, which can contribute to excessive red blood cell destruction, and helminth infections, a cause of excessive red blood cell loss, are geographically specific. Other infectious diseases also may be at play. There are contributing causes of anemia which include inadequate knowledge about the problem of anemia, environmental factors, lack of access to services, and poverty. Click here for a more complete list of direct and contributing causes of anemia.

Because there are different causes of anemia, an integrated package of interventions is recommended. In some cases, diagnosis of anemia may be warranted and appropriate to determine the cause of anemia.

What are the consequences of anemia?

An early symptom of anemia is fatigue and decreased ability to work (Haas & Brownlie, 2001). Yet, being anemia also is associated with an increased risk of mortality and cognitive loss in those who survive (Stoltzfus et al, 2005; Lozoff et al, 1988, 2000). Maternal anemia is associated with 20% of maternal deaths (Black et al, 2008), with greater evidence that anemia may cause increased blood loss at delivery and put women at risk of postpartum hemorrhage (Kavle et al, 2008). Anemic mothers are at greater risk of delivering premature and low-birth-weight babies who have an increased risk of dying (Kozuki, 2012; Zeng et al, 2008, 2009).

Giving iron during pregnancy reduces anemia and improves child outcomes. Indonesian children of mothers taking iron during pregnancy had a decreased risk of dying in their first five years of life, with a 40% decreased risk of dying in the first day of life (Dibley et al, 2012). Studies that administered iron and folic acid (IFA) supplements during pregnancy resulted in substantial impacts – halving neonatal mortality in China (Zeng et al, 2008) and markedly decreasing the risk of death in the first seven years of life (Christian et al, 2009).

Children younger than two years of age with severe anemia, caused by malaria and iron deficiency, are at increased risk of mortality (Brabin et al, 2001), and less milder forms, even if corrected, cause permanent cognitive damage by decreasing attention span and shortening memory. Children with anemia have, on average, IQs that are two points lower per every 10 g/L decrease in hemoglobin than other children (Black et al, 2008; Stoltzfus et al, 2004). Iron deficiency in U.S. school-age children is associated with poorer performance on math tests (Halterman et al, 2001).

Anemia has devastating costs to individual and national productivity. A 10% increase in hemoglobin in a moderately anemic person results in a 10-20% increase in work output (Levin, 1986). Eliminating anemia would increase adult productivity by 5-17% and gross domestic product by 2% in countries where anemia prevalence is high (Strauss et al, 1998; Horton et al, 2000). To achieve strides in preventing the consequences of anemia, an integrated package of interventions needs to be delivered at-scale to address all the causes of anemia.