Fat around the organs decides who gets hurt by the ultrafine soot in traffic exhaust

People carrying excess fat around their abdominal organs are the ones who benefit from filtering ultrafine soot out of their air, while lean, healthy people see almost no measurable difference, according to a study by researchers at the University of Connecticut and Tufts University. The paper, published July 28 in the American Journal of Preventive Cardiology, tracked 116 people living near a Massachusetts highway who used either a real HEPA air filter or a sham filter for 30 days, then switched to the other for another 30 days.

Ultrafine particulate matter, the smallest fraction of traffic exhaust at under 100 nanometers across, is already linked to heart disease, dementia and high blood pressure because it is small enough to slip into the bloodstream and travel through the body. What the new study adds is a way to predict, before anyone spends money on a filter, who is actually likely to benefit from one.

116 residents near Interstate 93 test HEPA filters

Doug Brugge, an environmental health researcher at the UConn School of Medicine, has spent years working with a community living within 200 meters of Interstate 93 just north of Boston, where ultrafine particulate exposure runs far higher than the U.S. average. His team recruited 116 residents from that community for the crossover trial, measuring blood levels of inflammation-linked proteins before and after each 30-day filter period to judge whether the HEPA units made a difference.

Averaged across all 116 participants, the filters made no detectable difference. That null result, on its own, would have suggested HEPA filtration simply doesn’t help this population. It was only when Brugge and a Tufts collaborator broke the group apart by body composition that a clear pattern emerged.

The trial’s broader cardiovascular findings were not entirely new by the time the visceral-fat analysis appeared. In August 2025, the American College of Cardiology had already covered an earlier readout from the same near-highway research in a summary titled “Air Purifiers May Reduce Heart Risks for People Exposed to Traffic Pollution.” The visceral-fat breakdown is the piece that explains why that earlier benefit showed up for some participants and not others, rather than a wholly separate result.

Misha Eliasziw traces the risk to visceral fat, not BMI

Misha Eliasziw, a biostatistician at Tufts University, was reviewing the trial’s data with Brugge when she noticed that the people who benefited from the HEPA filter all shared one trait: excess visceral fat, the fat that surrounds abdominal organs rather than sitting just under the skin, estimated from waist circumference relative to height and weight. Eliasziw considers that measure a sharper predictor of harm than body mass index, which factors in lean muscle along with fat and does not distinguish where fat sits on the body.

Eliasziw said it has only recently become clear that the amount of fat surrounding a person’s organs, more than overall body size, drives the risk of serious conditions such as heart disease, type 2 diabetes and certain cancers. The published paper ties that excess visceral fat to the release of inflammatory proteins called cytokines, including one known as IL-1 beta.

Doug Brugge on IL-1 beta and who benefits

“In the initial analysis, there was no association between HEPA filtration and cytokines,” Brugge said. “But in people who had excessive visceral fat, there was a strong IL-1 beta connection.” IL-1 beta sits near the start of an inflammatory chain that researchers link to cardiovascular disease, dementia and other circulatory and metabolic illness, which is why a filter that lowers it for one group but not another produces such different real-world outcomes.

Brugge summarized the practical split plainly: people who are lean and healthy are unlikely to see much benefit from a HEPA filter, while people carrying excessive visceral fat probably will. The same research team found a similar split when they looked at blood pressure and cognitive performance, where not everyone improved on the HEPA filter, but people with elevated blood pressure or older participants did.

A cheaper filter trial begins in Hartford and Boston

Commercial HEPA units can cost enough that knowing in advance who is likely to benefit has practical value, which is part of why UConn Today reported that Brugge and Eliasziw are now starting a clinical trial in Hartford and Boston built around inexpensive homemade filters, assembled from four air filters strapped to a box fan, a design that has already been used successfully in other settings and costs a small fraction of a commercial unit to build. The new trial will test whether the same visceral-fat pattern holds when the filtration comes from a low-cost build rather than a commercial one, and whether the benefit extends to cognitive performance and blood pressure the way it did in the original cohort.

An accompanying editorial published Sept. 12 in the same journal discussed the paper’s implications alongside it, underscoring that the visceral-fat finding was significant enough to warrant separate commentary rather than passing as a routine subgroup result. The original study was funded by the National Institute of Environmental Health Sciences and the UConn School of Medicine.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.