A new study links pollution exposure to increased body weight and respiratory disease, in a cycle in which polluted air contributes to weight gain and excess weight further harms lung function.
Published Nov 29, 2025 | 7:00 AM ⚊ Updated Nov 29, 2025 | 7:00 AM
Synopsis: Teenagers in Delhi are far more likely to be, obese and affected by respiratory illnesses than their peers in Kottayam and Mysuru, with a new study linking the capital’s severe air pollution to both higher body weight and poorer lung health. Researchers found that chronic exposure to polluted air disrupts hormones and increases inflammation, driving obesity, which in turn worsens respiratory symptoms and leaves many children with undiagnosed asthma.
Chronic exposure to polluted air disrupts hormones, triggers inflammation and alters metabolism, all of which increase the risk of obesity. This in turn worsens respiratory conditions, according to a new study.
Teenagers in Delhi, one of the most polluted cities in the world, are more than twice as likely to be obese compared with teenagers in the two southern cities studied by the researchers: Kottayam in Kerala and Mysuru in Karnataka.
Overall, 39.8 percent of adolescents in Delhi were overweight or obese, compared with 16.4 percent in the two southern cities.
The study published in Lung India examined 3,157 schoolchildren aged 13 to 17 across the three cities. All participants underwent spirometry testing. The findings linked pollution exposure to increased body weight and respiratory disease, creating a cycle in which polluted air contributes to weight gain and excess weight further harms lung function.
“Delhi is one of the most polluted cities in the world with annual average ambient PM10 and PM2.5 levels exceeding the World Health Organisation standards by over 15 fold,” the authors note.
Delhi is home to over 60 lakh children. Previous studies using questionnaires reported asthma prevalence between 4.6 percent and 15.7 percent among Delhi schoolchildren. The current research shows much higher rates.
More than half of the national capital’s adolescents, 50.9 percent, reported cough in the last three months, compared with 35.4 percent in Kottayam and Mysuru.
Shortness of breath affected over 30 percent of Delhi teenagers in the previous 12 months. Chest tightness, itchy skin, sneezing and watery eyes all occurred significantly more frequently in the capital. Eczema cases reached nearly five times the rate seen in the southern cities.
The spirometry results exposed a gap between symptoms and diagnosis. When researchers used questionnaires alone, asthma rates appeared similar across all three cities at around 21 percent.
But spirometry revealed that 29.4 percent of Delhi teenagers had airway obstruction suggesting asthma, compared with 22.6 percent in Kottayam and Mysuru.
“When asthma was defined using the ISAAC questionnaire, there was no difference in the prevalence rates between children living in D and K-M (21.7 percent vs. 21.5 percent),” the researchers noted.
“However, when spirometry was used to define airflow obstruction/asthma, the prevalence of asthma was significantly higher among children living in Delhi.”
The questionnaire, which focuses primarily on wheeze, underdiagnosed asthma in Delhi by 34.5 percent.
Among Delhi children with measurable asthma on spirometry, 88 percent had never received a diagnosis. Only 3.3 percent used inhalers. In Kottayam and Mysuru, 73 percent remained undiagnosed, with 8 percent using inhalers.
These figures match data from 22 years earlier, showing that diagnosis and treatment rates have not improved despite medical advances. Lakhs of Delhi’s children live with compromised breathing without knowing they have a treatable condition.
Body mass index stood out as the only factor that consistently predicted asthma across all three cities. Overweight and obese adolescents faced 1.79 times the odds of airway obstruction, and the effect was stronger in Delhi.
“In the total study population, children who were overweight/obese had significantly greater odds of having spirometrically defined airflow obstruction,” the researchers found. The odds ratio climbed to 1.38 specifically for Delhi’s overweight children compared to those in the south.
The authors traced multiple pathways linking pollution to weight gain. Polyaromatic hydrocarbons from vehicle exhausts function as endocrine disruptors that hijack hormonal networks controlling appetite and metabolism. They alter insulin sensitivity and lipid processing.
Research from the past decade documents how prenatal and postnatal exposure to air pollutants triggers childhood obesity through physical inactivity, oxidative stress, activation of stress hormone systems, changes in gut bacteria and genetic modifications. One US study attributed 23 percent to 28 percent of new childhood asthma cases directly to obesity.
International research confirms that excess weight is associated with asthma symptoms, eczema, rhinitis and greater airflow obstruction. Recent findings show obesity amplifies the harm of air pollution on children.
“It is tempting to speculate that chronic exposure to high levels of air pollution in Delhi led to the development of higher BMI, which further enhanced the risk of developing asthma and allergic diseases,” the authors wrote.
Delhi adolescents demonstrated higher lung volumes than their southern peers despite showing more obstruction. Their FEV1 and FVC measurements exceeded those of teenagers in Kottayam and Mysuru.
Delhi children measured taller and heavier than their southern counterparts, despite being two months younger on average. Height correlates with lung size, which may explain the volume difference even as airways narrow from inflammation.
Kottayam and Mysuru showed higher rates of preserved ratio impaired spirometry, a pattern indicating reduced lung capacity without obstruction. The study controlled for spirometry quality across all sites, using identical ultrasonic flow sensor equipment and trained staff. The equipment stored all data and transmitted measurements directly to quality assurance centres.
The research supports using an FEV1/FVC ratio below 0.85 as the cutoff for diagnosing airflow obstruction in adolescents. This threshold balanced sensitivity and specificity, and correlated strongly with symptoms including shortness of breath, wheeze and cough.
Previous studies showed the 0.70 cutoff had very low sensitivity, just 2.7 percent in one UK study, missing most asthma cases in children. The 0.90 threshold caught more cases but generated too many false positives.
Asthma affected boys 2.4 times more frequently than girls across all three cities. This pattern held regardless of location or pollution exposure. Earlier research suggested the gender gap reverses during puberty, but the study found no such transition.
The research enrolled 4,361 students from 12 schools, three in Delhi, six in Kottayam and three in Mysuru. Of these, 3,456 consented to participate, yielding a 79.2 percent response rate. The final analysis included 928 students from Delhi, 1,040 from Kottayam and 1,189 from Mysuru who completed questionnaires and performed quality spirometry.
Delhi children were younger by two months but measured significantly taller and heavier. Their average BMI reached 22.1, compared with 19.5 in Kottayam and Mysuru.
The authors acknowledged limitations, particularly the lack of adequate air pollution data from Kottayam and Mysuru to perform multiple regression analysis linking specific pollutants to health outcomes.
“Adolescent school children living in the polluted city of Delhi were significantly more overweight and obese than children living in the cleaner South Indian cities of Kottayam and Mysore, accompanied by the higher prevalence of self-reported respiratory symptoms, allergic rhinoconjunctivitis, eczema, and spirometrically defined asthma,” the authors concluded.
They called for further exploration of connections between air pollution, obesity and asthma in low and middle-income countries, where lakhs of children breathe polluted air while health systems struggle to diagnose and treat resulting conditions.
“Although we could not perform multiple logistic regression analysis with various air pollutants and health indices, including BMI, because of lack of adequate air pollution data from Kottayam and Mysore, it is tempting to speculate that chronic exposure to high levels of ambient air pollution increases BMI among urban adolescent children, which further enhances the development of asthma and allergic diseases,” the authors wrote.
(Edited by Dese Gowda)
