Exposure to high levels of air pollution increased stress hormone levels and negative metabolic changes in otherwise healthy, young adults in a recent study conducted in China. Air purifiers appeared to lessen the negative effects, according to new research published in the American Heart Association’s journal Circulation.Researchers focused on fine particulate matter (PM2.5) – a component of air pollution emitted from vehicles, factories, power plants, fires and smoking – because many studies have suggested this type of major air pollutant might lead to cardiovascular and metabolic health consequences, according to Haidong Kan, M.D., Ph.D., study author and professor of environmental health sciences at Fudan University in Shanghai, China.