A new study by an international team including University College London (UCL) researchers, has found that long-term exposure to toxic air can substantially weaken the health benefits of regular exercise.

Findings of the study are published in the journal ‘BMC Medicine’. The study which analysed data from more than 1.5 million adults tracked for more than a decade in countries including the UK, Taiwan, China, Denmark and the United States, found that the protective effect of regular exercise on people’s risk of dying over a specific period—from any cause and from cancer and heart disease specifically—appeared to be reduced, but not eliminated, for those who lived in high pollution areas.

The researchers looked at levels of fine particulate matter—tiny particles known as PM2.5 with a diameter of less than 2.5 micrometers across. These particles are so small they can get stuck in the lungs and enter the bloodstream, reported the’Medical Xpress’.

The health benefits of exercise significantly weakened, the team found, where the yearly average level of PM2.5 was 25 micrograms per cubic meter (μg/m³) or higher. Nearly half (46 per cent) of the world’s population live in areas exceeding this threshold.