New York, Nov 7 : The risk of heart attack, chest pain and related hospitalisation is higher during winter compared to summer, shows a study, amid the increasing air pollution levels in India, particularly in the national capital. The study explained that the rising levels of PM2.5 during winter inversions is a weather phenomenon where a mix of cold and warm fronts trap air pollution from motor vehicles, factory emissions and other human sources. The study found for heart attacks, there was a significant association between elevations in PM2.5 air pollution and increased same-day hospitalisations during the wintertime -- 10 per cent higher for each person in the population on each day they were exposed to an orange-level air quality index for PM2.5 air pollution compared to the green-level air quality index. Orange-level air quality is categorised as unhealthy for people in sensitive populations -- people with heart or lung disease, children and teenagers, people who are active outdoors and older adults. Green-level air quality is considered as posing little to no public health risk. Rise in air pollution during winters also raised the risk of unstable chest pain. However, they were most likely to wait up to two weeks before seeking medical treatment. Further, the study showed that pollution brought majorly by wildfires during the summer season raises no significant risk in hospitalisations for heart attacks. However, it raised the risk of an increase in unstable chest pain. For unstable chest pain, during the summertime, same-day risk of hospitalisation was about 45 per cent higher for each person in the population on each day they were exposed to an orange-level air quality index for PM2.5. "Air pollution is widely recognised as a significant contributor to cardiovascular disease and death and one we can modify by reducing exposure. Reversing the negative impacts of poor air quality on cardiovascular health is essential," said Joel D. Kaufman, Professor of environmental and occupational health sciences at the University of Washington in Seattle. "Summertime wildfire smoke does not cause the PM2.5 to rise as much as pollution from human sources during the winter inversions. However, the biological response to the particulate matter that is produced by wildfire smoke has been shown to be different from the response of PM2.5 produced by other sources, such as cars and businesses," added lead study author Benjamin D. Horne, from the Intermountain Medical Center Heart Institute in Salt Lake City, Utah. The findings will be presented at the American Heart Association's Scientific Sessions 2023, to be held between November 11 and 13, in Philadelphia. For the study, the team evaluated health records for nearly 22,000 adults (average age of 66 years) who were treated for heart attack or unstable chest pain between 1999 and 2022 at 11 hospitals. /IANS