(CNN) More than 95% of the world's population is breathing unhealthy air and the poorest nations are the hardest hit, a new report has found.

The report says exposure to air pollution led to strokes, heart attacks, lung cancer and chronic lung disease, causing many of those premature deaths.

It also says that air pollution is the fourth-highest cause of death among all health risks globally, coming in below high blood pressure, diet and smoking.

Indian commuters make their way through heavy smog in Amritsar in November, 2017.

"Air pollution takes a huge personal toll worldwide, making it difficult to breathe for those with respiratory disease, sending the young and old to hospital, missing school and work, and contributing to early death," Bob O'Keefe, vice president of HEI, said in a statement.