People living with air pollution have higher rates of depression and suicide, a systematic review of global data has found, The Guardian reports.

Cutting air pollution around the world to the EU’s legal limit could prevent millions of people becoming depressed, the research suggests. This assumes that exposure to toxic air is causing these cases of depression. Scientists believe this is likely but is difficult to prove beyond doubt.

The particle pollution analysed in the study is produced by burning fossil fuels in vehicles, homes and industry. The researchers said the new evidence further strengthened calls to tackle what the World Health Organization calls the “silent public health emergency” of dirty air.

“We’ve shown that air pollution could be causing substantial harm to our mental health, making the case for cleaning up the air we breathe even more urgent,” said Isobel Braithwaite, at University College London (UCL), who led the research.

Meeting the EU limit could make a big difference, she said. “You could prevent about 15% of depression, assuming there is a causal relationship. It would be a very large impact, because depression is a very common disease and is increasing.” More than 264 million people have depression, according to the WHO.

“We know that the finest particulates from dirty air can reach the brain via both the bloodstream and the nose, and that air pollution has been implicated in increased [brain] inflammation, damage to nerve cells and to changes in stress hormone production, which have been linked to poor mental health,” Braithwaite said.

Joseph Hayes, also at UCL and part of the research team, said: “The evidence is highly suggestive that air pollution itself increases the risk of adverse mental health outcomes.”