By Saumya Joseph

(Reuters Health) – Air pollution has often been linked with increased heart disease risk, but a “natural experiment” involving travelers to a city much more polluted than their own offers clues to how it may harm blood vessels over time, researchers say.

In 26 healthy young adults from Los Angeles, researchers measured blood levels of pollution breakdown products and proteins linked to heart risk before, during and after a trip to Beijing for a summer study program.

Over six to eight weeks in the Chinese capital, pollution metabolites in participants’ urine spiked along with blood markers of inflammation and artery plaque buildup, the study team reports in the journal Circulation.

These results are “lending more evidence that the (heart disease) pathways that have been observed in animals, now could be happening in humans,” noted Erika Garcia, an environmental health researcher at the University of Southern California in Los Angeles, who was not involved in the study.

Air pollution is a serious public health problem in China, where it adversely affects the heart health of the 1.4 billion residents, the study team notes.

Past research has linked long-term exposure to air pollution with heart disease and early death, they write. Studies in animals have also linked particle pollution with atherosclerosis, or hardening of the arteries, due to plaque build-up. The effects of exposing people to air pollution for shorter periods have not been well studied, however.

To see whether even a short shift from a less-polluted environment to a more-polluted one would affect so-called biomarkers that are known to be involved in heart disease, the researchers took advantage of a study-abroad summer program run by the University of California, Los Angeles (UCLA) and the University of Peking in Beijing.

They recruited 26 non-smoking, healthy UCLA students, with an average age of 24, who visited Beijing for 10 weeks in 2014 or 2015.

Urine and blood samples were collected from the students about a week before their departure from L.A., six to eight weeks after their arrival in Beijing, and four to seven weeks after they returned to L.A.

While the students were in Beijing, tiny-particle air pollution levels averaged 371% higher than in L.A. and pollution breakdown products in the students’ urine rose to concentrations 176% to 800% higher than they had been in L.A., the study found.

Activity by enzymes that promote HDL, the “good” cholesterol, was impaired while students were in Beijing, although students’ HDL levels remained unchanged, the researchers report. Fibrinogen, a blood marker of inflammation, rose by nearly 50%, and C-reactive protein (CRP), another inflammation marker, nearly doubled while the students were abroad. Markers of blood-fat oxidation, which contributes to plaque buildup, rose as well.

By the six-week mark in Beijing, air particulate matter had already had a significant effect on students’ biomarkers and the pathways involved in atherosclerosis and development of heart disease had been “activated,” Dr. Jesus Araujo, a cardiologist at the David Geffen School of Medicine at UCLA and the study’s senior author, told Reuters Health.

“We can (now) have a sense of when a person would be affected by the increased exposure as opposed to waiting for many months or years and later on when the damage has already been done,” he said in a phone interview.

The effects of exposure in Beijing were largely reversed after the students returned to Los Angeles. But it is still not known whether short-term visits to places with severe air pollution could raise the risk of developing chronic cardiovascular disease, the study authors note.

Travelers to countries with severe air pollution such as India and China could try remaining indoors, using air purifiers and avoiding physical activity outdoors, Araujo advised.

He said research aimed at identifying people who are most susceptible to developing cardiovascular diseases as a result of exposure to pollution could have important implications for developing preventive measures.

Garcia said preventive measures at an individual level are not enough unless national air pollution levels are brought under control. “From the public health standpoint, prevention is going to be much more cost effective and much more impactful if we target the full population.”

SOURCE: Circulation, online November 20, 2019.