Slimming down is tough.
Even if you exercise regularly and eat well, you may still get different (and possibly disappointing) results than someone who follows the same regimen.
What causes this disparity? There are many answers, but one of the most invisible causes may be going straight into your body without you knowing it – air pollution.
Particles disrupt appetite-governing hormones
The idea of microscopic airborne particles causing you to gain weight seems like science fiction, but the science is solid.
Fine particles, measuring less than 2.5 microns across, and ultrafine particles, less than 0.1 microns across, are believed to be the pollutants most responsible for disrupting metabolic function.
When you breathe in, particle pollutants irritate the alveoli in your lungs that normally allow oxygen to pass into your blood stream. Consequently, the lining of your lungs releases hormones that make insulin less effective, diverting blood from insulin-sensitive muscle tissue and stopping your body from properly regulating its blood sugar levels.
Additionally, particle pollution may cause your body to flood your blood with higher levels of inflammatory molecules called “cytokines”, which trigger immune cells to invade otherwise healthy tissue.
According to a 2014 study published in Environmental Health, this response not only interferes with your tissue’s ability to respond to insulin, but the resulting inflammation may also disrupt the hormones and brain processing that govern your appetite.1
This can result in feeling hungry even when you’re totally full, and the additional food you eat to feed your artificial appetite may result in weight gain over time – the Berkeley researchers found, in fact, that air pollution exposure could lead to a 13.6% increase in body mass index (BMI), the most popular metric for a healthy weight.
This pollution-triggered inflammation may also lead to a host of health issues, such as:2
But how have researchers established a link between air pollution and obesity? As with many scientific breakthroughs, the earliest evidence came out of animal studies that hinted at physical responses to airborne pollutants.
Studies link air pollution and obesity
A 2010 study in Arteriosclerosis, Thrombosis, and Vascular Biology first tackled this question while looking into how living in big cities could put people at a higher risk of heart disease compared to their countryside counterparts.3
In the study, some mice were given clean, filtered air to breathe while others were exposed to the kind of dirty air you’d find near a congested freeway. The researchers periodically weighed the mice and performed tests to analyze their metabolic function.
In just 10 weeks, the mice exposed to the polluted air displayed greater volumes of body fat, both around their midsections and around internal organs, and the fat cells were approximately 20% larger in the mice exposed to polluted air.
The fatter mice also seemed to have become less sensitive to insulin — one of the first symptoms in the development of type 2 diabetes.
Several scientific studies show that humans are susceptible to the same alarming health consequences.
Air pollution may lead to obesity and other health problems
A particularly noteworthy study examined the medical records of 62,000 people in Ontario, Canada over a 14-year period.4
The researchers discovered that the risk of developing diabetes increased by roughly 11% for every 10 micrograms of fine particles in a cubic meter of air — this is a disturbing figure considering that PM2.5 pollution in some cities and regions affected by wildfires have been recorded at 500 micrograms per cubic meter of air.5
A 2015 study in PLOS One offered similar evidence of increased hypertension, insulin resistance, and waist circumference in a sample of almost 4,000 people living in a highly polluted area.6
Children are also vulnerable
Scientists are specifically concerned that air pollution may alter the metabolism of infants and young children, making them more likely to become obese as they age.
A 2012 longitudinal study published in American Journal of Epidemiology addressed this question by examining the health nearly 800 children growing up in the Bronx borough of New York City from 1998 to 2006.7
This study was designed to be as rigorous as possible to make sure results were accurate and revealing – while pregnant, the children’s mothers wore a small backpack that measured the air quality as they carried on with their day, and over the next seven years the children’s health was monitored at regular intervals.
Accounting for other factors like diet and income, the children born in the most heavily polluted areas were 2.3 times likelier to be considered obese, compared to children living in neighborhoods with cleaner air quality.
Further supporting these findings, a 2017 study in Pediatric Obesity demonstrated that even in the first six months, babies of mothers living in heavily polluted areas appear to put on weight more rapidly than those in areas with cleaner air.8
It’s important to be cautious about giving too much weight to these findings — the studies only establish a link between exposure and outcome but can’t prove that one factor causes another.
But researchers continue to uncover key findings that fill those gaps.
A 2016 study published in Hypertension tested a small group of subjects in Beijing for two years.9 The researchers discovered that whenever the big city’s notorious smog blanketed the sky, telltale indicators of developing issues like insulin resistance and hypertension peaked — providing more concrete evidence that the air quality may be directly linked to metabolic processes that lead to obesity.
Air pollution is a global issue
As scientific research continues to shed more light on the link between air pollution exposure and obesity, what can you do to protect yourself from such a seemingly omnipresent threat to your health?
The scientific community emphasises that the individual, short-term risk posed by poor air quality shouldn’t be understood as the basis for obesity by itself without considering other facets of your lifestyle, such as diet or physical activity.
However, given the vast amount of people living in cities plagued with air pollution — up to 68% of the world’s population by 2050, according to the United Nations — the long-term risk could be massive.10
When it comes to positively impacting your air quality as well as your weight, focus on the change you can make in your own world.
The global air pollution crisis is obviously impossible for a single person to crack. On a global scale, some other measures that could help improve air quality include:
- restrict traffic in densely populated urban areas to reduce traffic pollution
- redesign streets to make them friendlier to pedestrians and cyclists
- increase investment in renewable energy sources, such as wind and solar
Losing weight is challenging enough without having to worry about invisible pollutants wreaking havoc on your metabolism.
While outdoor air pollution is out of your immediate control, you can take control of your indoor air quality by monitoring your indoor air quality, especially levels of harmful PM2.5, and making positive changes in your life today.
A healthy diet and regular exercise are still the most vital keys to success in your weight-management journey, but a little clean air might help boost your overall health and wellness.
IQAir is a Swiss-based air quality technology company that since 1963 empowers individuals, organizations and communities to breathe cleaner air through information, collaboration and technology solutions.
 Jerrett M, et al. (2014). Traffic-related air pollution and obesity formation in children: A longitudinal, multilevel analysis.
 Niemann B, et al. (2017). Oxidative stress and cardiovascular risk: Obesity, diabetes, smoking, and pollution: Part 3 of a 3-part series.
 Xu X, et al. (2010). Effect of early particulate air pollution exposure on obesity in mice: role of p47phox.
 Chen H, et al. (2013). Risk of incident diabetes in relation to long-term exposure to fine particulate matter in Ontario, Canada.
 Beijing air pollution at dangerously high levels. (2014).
 Eze IC, et al. (2015). Long-term exposure to ambient air pollution and metabolic syndrome in adults.
 Rundle A, et al. (2012). Association of childhood obesity with maternal exposure to ambient air polycyclic aromatic hydrocarbons during pregnancy.
 Fleisch AF, et al. (2016). Prenatal and early life exposure to traffic pollution and cardiometabolic health in childhood.
 Brook RD, et al. (2015). Extreme air pollution conditions adversely affect blood pressure and insulin resistance: The air pollution and cardiometabolic disease study.
 2018 revision of world urbanization prospects. (2018). https://www.un.org/development/desa/publications/2018-revision-of-world-urbanization-prospects.html