Small Particulates Associated with Lower Respiratory Infections

A large-scale observational study

By Julianne Forbes, ND

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Horne BD, Joy EA, Hofmann MG, et al. Short-term elevation of fine particulate matter air pollution and acute lower respiratory infection [published online ahead of print April 13, 2018]. Am J Respir Crit Care Med.


To evaluate the association between ambient small particulate matter (PM2.5) levels and healthcare encounters for acute lower respiratory infections (ALRI) among very young children, with a secondary objective of finding the same associations for older children, adolescents, and adults.


Observational case-crossover design


The study included more than 146,000 individuals of all ages and sexes living in a narrow swath of urban/suburban land in north central Utah known as the Wasatch Front. The area experiences great variability in PM2.5 concentrations due to regular wintertime temperature inversions and is home to more than 80% of Utah’s population.

Inclusion criteria was based on diagnosis of acute lower respiratory infection (ALRI) during the study period (1999-2016). The majority (77%) of the participants were children aged 0 to 2 years.

Study Parameters Assessed

Particulate matter concentrations were measured using community-based air quality monitors between 1999 and 2016.

Primary Outcome Measures

Short-term periods of PM2.5 elevation were matched with the timing of increases in reported encounters based on healthcare visits for ALRI. The population was grouped by age ranges (0-2, 2-17, and ≥18 years). After stratification by age range, odds ratios (ORs) for ALRI were calculated based on healthcare encounters.

Key Findings

Short-term exposure to elevated PM2.5 air pollution was associated with greater healthcare utilization for ALRI in young children, older children, and adults.

Encounters for ALRI in the young children increased within 1 week of elevated PM2.5, with another peak after 3 weeks. The cumulative 28-day OR was 1.15 per 10 μg/m3 increase in PM2.5 (95% confidence interval [CI]: 1.12-1.19). Similar elevated odds for ALRI were observed for older children.

Short-term exposure to elevated PM2.5 air pollution was associated with greater healthcare utilization for ALRI in young children, older children, and adults.

There were also increases in diagnosed and laboratory-confirmed respiratory syncytial virus (RSV) (especially in the young children) and influenza-related encounters (especially among older children and adults) following elevated ambient PM2.5 levels.

Practice Implications

Lead investigator Dr Horne, while speculating about the connection between PM2.5 and ALRI, said the following: "The air pollution itself may make the human body more susceptible to infection or may impair the body's ability to fight off the infectious agents. It may be that PM2.5 causes damage to the airway so that a virus can successfully cause an infection or that PM2.5 impairs the immune response so that the body mounts a less effective response in fighting off the infection.”1

There are many naturopathic methods to support immune function in children and adults, including a lifelong habit of consuming a healthy, whole foods–based, phytochemical-rich diet. Several studies indicate that air pollution exposure results in increased oxidative stress and that dietary supplementation may play a modulating role on the acute effect of air pollutants. For example, one study suggested B vitamins may lessen untoward effects of airborne particulates in some people. Other nutrients like vitamin C, vitamin E, vitamin D, and omega-3 polyunsaturated fatty acids (PUFAs) have shown protective effects against the damage induced by particulates in air-polluted environments,2 and antioxidant-rich, colorful fruits and vegetables have improved resilience in asthma conditions.3

Lung conditions such as asthma may be worsened or triggered by airborne particulate matter. Observational studies suggest that those who consume omega-3 PUFAs are less likely to develop asthma. Preclinical studies corroborate this observation, showing that omega-3 PUFAs protect against asthma triggers, including viruses4 and allergens.5 However, no interventional studies have examined the effect of omega-3 fatty acids on asthma exacerbation risk.6 It should be noted that supplementation with omega-3 PUFAs alone may increase susceptibility to oxidative damage.7 For this reason, supplementation with omega-3 PUFAs in combination with antioxidants is warranted.

There may be other explanations besides direct effects of particulates on the lungs to explain the association between increased particulates in the air and lung infections. According to Horne, air pollution–induced lung damage “could lead to longer periods of ALRI symptoms or more severe symptoms requiring a higher intensity of medical care for the infected individual. It may also be that periods of acute increases in PM2.5 lead people to stay indoors more where they are in closer contact with others who carry infectious agents and can transmit the infection to them."1

As an extension of these thoughts, more indoor time can also contribute to insufficient vitamin D production by reducing sun exposure. Reduced vitamin D status may also be exacerbated by air pollution itself, which can prevent ultraviolet (UV) radiation from penetrating the atmosphere resulting in a similar net effect of low vitamin D status.8 A recent intervention trial has been conducted using vitamin D in asthma, which found that the rate of first exacerbation was reduced in subjects who demonstrated an increase in circulating vitamin D following supplementation,9 suggesting the potential for vitamin D to protect against air pollution–induced exacerbations.

Prevention of ALRI and amelioration of symptoms may be achieved by alerting the public to an acute increase in the level of PM2.5. When this occurs, people may be able to prevent infections or decrease ALRI symptom severity or duration by reducing their exposure to the air pollution.10 For example, people may be warned to be more vigilant in not touching their face without first washing their hands, and to engage in other preventive behaviors that are known to reduce infection risk.1

The potential health and economic benefits of establishing nonpharmacological approaches (eg, reduced exposures, hygiene considerations, and dietary supplementation) to disease management are enormous. Further studies are needed to determine how various combinations of nutrients may minimize the impact of airborne particular matter, especially PM2.5, on various aspects of lung health.

About the Author

Julianne Forbes, ND received her degree at National College of Naturopathic Medicine and practices in North Bridgton, ME where she focuses on rural family health among the oldest demographic population in the nation.


  1. American Thoracic Society. Brief exposure to tiny air pollution particles triggers childhood lung infections. Published April 13, 2018. Accessed May 27, 2018.
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