By Piriya Mahendra
Exposure to ozone for as little as 2 hours could induce physiologic changes associated with cardiovascular disease, say US researchers.
Their study findings imply that exposure to ozone could be a major cause of the 2 million deaths associated with air pollution that occur worldwide.
Robert Devlin (US Environmental Protection Agency, North Carolina) and team found that individuals exposed to 0.3 parts per million (ppm) of ozone showed a significant increase in blood levels of interleukin (IL)-1β, a decrease in plasminogen activator inhibitor 1 (PAI-1) and plasminogen, and changes in heart rhythm, immediately after exposure and during the following morning.
Specifically, they experienced a 55.7% increase in IL-1β immediately after exposure and a 103.8% increase 24 hours after exposure. There was a 32.8% decrease in PAI-1 levels immediately after exposure, which persisted for 24 hours, after which there was a 42.7% decrease. In addition, a 41.5% decrease in plasminogen levels occurred immediately after exposure.
The study included 23 individuals aged 19-33 years who underwent two controlled exposures - one to clean air and one to ozone - at least 2 weeks apart. During each exposure, participants alternated 15-minute periods of stationary cycling and rest.
The results also showed that a 51.2% reduction in the high frequency (HF) component of heart rate variability occurred immediately after ozone exposure and a trend toward decreased HF was present 24 hours following exposure. There was also an ozone-induced 5.8% decrease in the complexity of the QRS wave immediately following exposure.
As reported in Circulation, none of the participants reported complaints or physical symptoms after inhaling ozone and there were no significant changes in biomarkers after exposure to clean air.
"This study provides a plausible explanation for the link between acute ozone exposure and death," commented Devlin in a press statement.
He added: "People can take steps to reduce their ozone exposure, but a lot of physicians don't realize this."
According to current Environmental Protection Agency guidelines, when the Air Quality Index shows that ozone levels are unhealthy, individuals should avoid exposure to ozone by reducing the time they are active outdoors and limiting outdoor activity to the morning or evening.
They should also substitute intense activities such as playing basketball and chopping wood for less intense activities such as playing tennis and doing light garden or construction work.
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