Air pollution is pervasive, and around the world, more than 90% of children under 15 are exposed to unhealthy air. Stunting—when a child is too short for his or her age—is also a major health threat: worldwide, one in five children under 5 suffer from stunting, with resulting health impacts that can include diminished cognitive development. The relationship between air pollution and child stunting has been largely overlooked but new research offers updated evidence on the link.
Vivian Pun, an epidemiologist in Vital Strategies’ Environmental Health division, along with colleagues Sumi Mehta and Russell Dowling, recently published a paper, “Ambient and household air pollution on early-life determinants of stunting—a systematic review and meta-analysis,” which reinforces the link between air pollution and stunting.
We spoke to Vivian Pun to learn more.
Why are children especially susceptible to air pollution? What are the health consequences of air pollution among children?
Children face unique risks from air pollution because their organs and respiratory and cardiovascular systems are still developing. In addition, children breathe in two to three times more air and at a faster rate than adults.
Air pollution is the second leading risk factor for death in children under 5 each year, killing 690,000 children in 2019, more than unsafe drinking water and poor sanitation combined. Recognized by the World Health Organization (WHO) as “an overlooked health emergency for children around the world,” air pollution can be especially severe for children living in low- or middle-income countries, where they may be exposed to higher level of pollution and more underlying disease.
The negative effects of air pollution on a child starts at the time of conception. Exposure during pregnancy is linked to decreased fetal lung growth and development, and increased risk of birth defects and adverse birth outcomes, including low birth weight. Air pollution exposure during childhood is also associated with reduced lung growth and lung function and higher risk of lower respiratory infections including pneumonia and lung diseases. These early life outcomes have prolonged impacts on health and can lead to increased risk of chronic respiratory illness, cardiovascular disease and diabetes throughout the child’s lifetime.
What is stunting and why is it so important to prevent it?
Stunting is a well-established indicator for poor child development. It is defined as a height of more than two standard deviations below the WHO child growth standards. Stunting can begin in utero, and manifests mostly during the first two years of a child’s life, with increasing prevalence until age 5. In 2019, an estimated 144 million children under 5 were stunted.
Stunting is a largely irreversible outcome with long-term impacts on children and their communities. Not only do stunted children experience diminished height and physical development, they often suffer from impaired cognitive and socioemotional development that can result in lower grades, anxiety, depression and lower self-esteem, as well as increased illness and early deaths. They also have lower lifetime earnings and assets. The most direct factors contributing to stunting are malnutrition and poor diets and sanitation among mothers and children; however, emerging environmental threats including air pollution have also been linked to increased risk of childhood stunting.
While precise biological mechanisms connecting air pollution with stunting remain to be determined, it is commonly hypothesized that prenatal and postnatal exposure to particulate matter—small inhalable particles that are known to pose the greatest risk to health—may increase oxidative stress, which can damage cells and DNA. This can also induce acute placental and pulmonary inflammation and coagulation, and alter endothelium regulating functions, all of which can lead to diseases and even deaths.
Particulate Matter: small inhalable particles that are known to pose the greatest risk to health
Can you tell me about your research on air pollution and stunting? How does your research build upon previous studies?
Much of our air pollution work at Vital Strategies focuses on India and Indonesia, both among the five countries with the highest burden of disease due to poor air quality levels. These are also the countries with some of the highest numbers of stunted children—36 million or 32% in India and 7.5 million or 32% in Indonesia. My colleagues and I wanted to better understand the potential link between air pollution and stunting, especially in these countries.
What we found was that while a number of epidemiologic studies had examined this association in different populations and settings, an updated review of previous study findings was not available, resulting in a gap between the latest research evidence and current clinical and public health policies. We decided to conduct an updated systematic review and meta-analysis to evaluate and summarize the findings of all relevant studies published over the past two decades on the association between air pollution and stunting. Systematic reviews make evidence more accessible to decision-makers by providing a complete synthesis of the available evidence, addressing questions and identifying gaps that warrant further research.
Unlike previous reviews, ours includes epidemiologic studies that assessed the impacts on stunting of ambient (or outside) air pollution and household air pollution, as well as studies on prenatal determinants of stunting. We also include results from 12 new publications, not analyzed in previous reviews, which focus on populations exposed to air pollutants concentrations several times higher than World Health Organization’s air quality guidelines. As a result, our review addresses key evidence gaps on the association between air pollution and stunting, especially for household air pollution and in countries where children are most vulnerable to stunting and its associated health and developmental impacts.
What new evidence does your research find?
Our review “Ambient and household air pollution on early-life determinants of stunting—a systematic review and meta-analysis” was published in the journal Environmental Science and Pollution Research in April.
Children living in low-and-middle income countries are disproportionately affected by indoor air pollution, often a result of their proximity to solid fuels in cooking and heating.
Based on a systematic review and quantitative assessment of 45 eligible studies from 29 countries published on or before August 2020, we found significant associations between children small for their age, and an increase in exposure to air pollutants over the entire pregnancy. The analysis also showed an 19% increased risk of postnatal stunting was associated with postnatal exposure to household air pollution from using solid fuels like wood and coal. This is especially dangerous for women and children living in low-and-middle income countries who are disproportionately affected by indoor air pollution, often a result of their proximity to solid fuels in cooking and heating.
The evidence reinforces the importance of promoting clean air, an often-overlooked contributor to stunting, as part of an integrated approach to preventing stunting and improving children’s health.
How can governments improve air quality and prevent childhood stunting?
Malnutrition is one of the most direct causes of stunting, so it is important that governments implement or strengthen public health programs to promote optimal breastfeeding and care practices as well as nutrition interventions to improve the health and nutrition of mothers and children.
Findings from our review also show the need for progress to reduce air pollution. Air pollution can be controlled with proven, evidence-based solutions aimed at major air pollution sources. Right now, many governments may be focused on COVID-19, but sustained efforts to improve air quality are urgently needed. Investments in air pollution control now will continue to benefit health and development long after the pandemic.
Governments and policymakers must prioritize air pollution control efforts in their jurisdictions through identifying leading sources of air pollution, investing in clean fuels and best available emission-reduction technologies, and implementing evidenced-based clean air policies to reduce emissions. Policies should also be equitable and consider who is most likely to be exposed and affected by air pollution, such as children and families who use solid fuels for cooking and heating. Practical and evidence-based resources including Vital Strategies’ Accelerating Clean Air Progress: Innovation and Action Guide can help governments rapidly reduce air pollution in the near term while working toward a more comprehensive air quality management plan.
Improvement in air quality through effective policy and action can ultimately reduce the likelihood of childhood stunting and its related impacts and protect millions of children around the world from issues with both physical and cognitive developmental.
To read the full paper visit: https://link.springer.com/article/10.1007/s11356-021-13719-7.
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