An assistant professor at the University of Massachusetts has concluded after a five-year study that high concentrations of air pollution increase health risks on obese people more than on people who are not obese.

Assistant Professor Srimathi Kannan of the nutrition department at UMass found that Detroit residents who lived closest to heavy traffic and other sources of pollution had higher pulse pressure.  Furthermore, those classified as obese registered the greatest increase in obesity rates from pollution, especially within the first 48 to 96 hours of exposure to pollutants. 

A team of five graduate students, six undergraduate students, eight phlebotomists, volunteers, three doctors, and Kannan carried out the study, which started in 2000, as part of the Health Environments Partnership (HEP). 

“I have always had an interest in conducting chronic disease research investigations around nutrition interactions with environmental exposures such as air pollution and its health effects on vulnerable populations,” said Kannan. 

She further explained that having grown up in an industrial township in India, her interest in the chronic disease-environmental factors connection sparked very early in life.

Having envisioned the Detroit HEP project with Dr. Amy Schulz, PI for the project, Kannan directed her lab-student teams to organize nutrition and biomarker community clinics in Eastside, Northwest and Southwest Detroit. All three areas of the city are ethnically and economically diverse and within five kilometers of an air quality monitoring site. Kannan and other researchers collected data on air quality and biomedical measures to form a conclusion. 

“My group collected biomarker samples (fasting blood, saliva and blood pressure) from the participants,” she said. “After each batch of biomarkers, data collection was completed, samples were transported from multiple study sites to my lab at UMich, (University of Michigan Ann Arbor) where the samples were further processed and prepared for assays,” said Kannan.

919 households were sampled from the three Detroit areas. Just over half of the 348 participants who agreed to give biomarker samples, composed of blood samples, blood pressure, weight, height and waist circumference, were obese. 57 percent of participants had waist circumferences above sizes indicative of high ill-health risk.  Two-thirds of the total sample had high blood pressure or were at risk of being diagnosed with it. 36 percent had high blood cholesterol.

“The results suggest that, after accounting for proximity to point sources of air pollution measured by fine particles, individuals with central adiposity, (an academic term for fat) are more sensitive to increased (blood pressure) in response to PM (particulate matter) exposure,” said Kannan. 

Kannan added that the results were somewhat consistent with her hypothesis; the research team was surprised to find evidence for increased health risk among the non-obese.  Overall, Kannan and the team concluded that exposure to certain pollutants increases the risk of obesity across different population groups.

“PM2.5 exposure increases risk among all segments of the population, with exacerbated risk among those with central adiposity,” she said. 

Kannan noted that central adiposity, or belly fat, was measured using waist circumference.  She also explained that the team was able to distinguish which high-risk people were suffering from pollutants and which ones were suffering from obesity. 

“How do we know that the high-pollution concentration causes it instead of obesity?” Kannan asked.  “We undertook an effect modification approach in data analysis and we used models that include the interactive effect of obesity and community-level air pollution exposure.” 

This means that the research group compared the systolic pressure, diastolic pressure, pulse pressure and arterial pressure of an obese person to models incorporating sodium intake, physical activity, medication use and air particles. 

“The observed effect of fine particles on multiple indicators of blood pressure was found to be enhanced by community proximity to point sources of fine particles and this effect is observed for those with elevated body mass index and waist circumference,” said Kannan.    

Kannan further pointed out that Southwest Detroit contains a high density of industrial facilities, including iron and steel manufacturing, coke ovens, chemical plants, refineries, sewage and sludge incineration and coal-fired utilities, relative to other areas of the city. 

Southwest Detroit also gets heavy car and truck traffic. Previous analyses found that more than 30 percent of the fine particles of the Southwest Detroit monitoring site were due to locally emitted particles from motor vehicles. Therefore, the particulate matter in Southwest Detroit is 20 percent higher than in the other Detroit locations.      

Kannan has recently published her findings in the Journal of Epidemiology and Community Health.  The study has also appeared in the Atlanta Journal-Constitution and Modern Medicine.com within the past week.

Kannan and other authors of the study say their findings suggest that obesity and a midriff bulge boost susceptibility to changes in blood pressure. These changes in blood pressure are also associated with environmental air pollution. 

High blood pressure increases the risk of heart disease and stroke. The authors note that obese people are already disadvantaged in terms of health and that exposure to high pollution multiplies their risks of serious ill health.

Researchers from the University of Michigan, the Detroit Department of Health and Wellness Promotion and the Detroit Hispanic Development Corporation were also involved in the study.

Kannan has been an assistant professor of nutrition at UMass School of Public Health and Health Sciences for three years.

Angela Hilsman can be reached at [email protected]