Two people can live in the same neighborhood, breathe the same air, and yet not suffer exactly the same consequences.
Researchers were interested in ultrafine particleswith a diameter of less than 100 nanometers, notably emitted by road traffic. Invisible to the naked eye, they can penetrate deep into the lungs and then enter the bloodstream.
These particles are associated with an increased risk of cardiovascular disease, hypertension, respiratory disease and dementia. But one question remains: why do some people seem more vulnerable than others?
These invisible particles put the inflammatory system on alert
To understand this phenomenon, we must follow the path of these tiny pollutants. Ultrafine particles can reach deep areas of the lungs and activate inflammation, which becomes chronic and can contribute to the development of cardiovascular and metabolic diseases.
Doug Brugge, a researcher at the UConn School of Medicine, therefore wanted to know if reducing exposure to these particles could modify this response.
His team recruited 116 inhabitants living less than 200 meters from Interstate 93, north of Boston, an area particularly exposed to automobile pollution. Each participant used a HEPA filter for 30 days, then a dummy device for 30 days.
- The filter effectively reduced the exposure: -65% for PM2.5 and -32% for ultrafine particles;
- However, across the entire group, the researchers observed no significant average drop in markers of inflammation (IL-1β, IL-6 or C-reactive protein).
The result could have ended there. But detailed analysis of the participants revealed an unexpected difference.
The detail that changes everything: the fat around the organs
Doug Brugge discussed the results of the study with Misha Eliasziw, biostatistician at Tufts University. According to Eliasziw’s analysis, the people who benefited from the HEPA filter shared a particular characteristic: they had excess visceral fat, that is, fat around the abdominal organs, as indicated by their waist measurement in relation to their height and weight. In the 12 people identified, one month of HEPA caused IL-1β to drop by 22.8%, from 0.179 to 0.138 pg/mL, which the standard BMI did not show.
“Initial analysis revealed no association between HEPA filtration and cytokines. However, in people with excess visceral fat, a strong correlation with IL-1 beta was observed.”explains Brugge.
According to the biostatistician, this measure of harmful fat was more relevant than the body mass index (BMI). BMI simply measures a person’s weight in relation to their height and includes lean muscle mass.
“Excess fat around organs has recently been found to increase the risk of serious illnesses, such as heart disease, type 2 diabetes and certain cancers.explains Eliasziw. Excessive fat accumulation around the abdominal organs causes the release of cytokines like interleukin-1 beta, which stimulates inflammation. This interleukin-1 beta initiates a series of reactions in the body, leading to cardiovascular disease, dementia and other conditions affecting the circulatory and metabolic systems.
Thin, healthy individuals probably won’t benefit much from HEPA filters. On the other hand, those who have excess visceral fat will definitely benefit.
Should you buy an air purifier?
The researchers also observed effects on the
blood pressuremainly in the elderly or those with hypertension. Similar trends were found regarding cognitive performance.
These results do not allow us to recommend the purchase of a HEPA purifier to everyone, but the study above all shows that
the response to pollution could depend on individual vulnerability. Remember, however, that the result concerning visceral fat is based only on
12 people. It will have to be confirmed on much larger numbers. However, researchers hope that future studies take more into account waist circumference and visceral fat, rather than BMI alone.
Behind this discovery lies an essential question: faced with the same pollution, we are perhaps not all exposed to the biological consequences in the same way. Better understanding this vulnerability could, ultimately, make it possible to better target protection measures.