Breathing in air pollution, and having asthma generally, may increase people's risk of suicide, according to two new East Asian studies.

In the first study, researchers from Taiwan showed that there was a statistical link between asthma and about 8% of suicides.

Wayne Katon, a psychiatrist at the University of Washington in Seattle, said that the study highlighted the negative effect pollution has on society.

He said that you could tell how hard life was for people by their suicide rate.

The researchers said that their study was the first to link air pollution to suicide risk.

However, it is not the first study to link air pollution to poor health.

Particle pollution from smoke, dust, and heavy metals has previously been linked to heart disease.

Other studies have also linked particle pollution to asthma severity.

For the Taiwanese researchers, it is a mystery why suicide risk should be linked to asthma and poor air quality.

Katon said that he believed one reason for the connection could be that the people who killed themselves were already vulnerable to a chronic disease.

Katon said that anyone who had a chronic illness should be screened for depression, since poor mental health went hand-in-hand with poor physical health.

In the second study, researchers in Korea also established a link between air particle pollution and suicide risk.

In analysing data from seven big Korean cities, the Korean researchers found that heavy air pollution was a factor for about 10% of 4,000 people who killed themselves.

Lead researcher Changsoo Kim, from the Yonsei University College of Medicine, said that particle pollution was known to cause inflammation in the body.

Leaving asthma out of the equation, Kim and his colleagues speculated that inflammation due to poor air quality caused depression, if people had underlying heart disease.

The Korean researchers said that, in their data set, people who had been treated for heart disease were fully 19% more likely to commit suicide.

Katon said that air pollution could cause people to misperceive their own health, making the issue of health a psychological problem.

Chian-Jue Kuo of the National Taiwan University and his colleagues said that linking suicide to asthma might well reflect more common levels of mental distress.

The researchers said that people needed to be aware of the link between suicide and asthma.

For their study, the Taiwanese researchers analysed data from about 163,000 high school students, taken over a 12-year span.

The researchers found that wheezing and other asthmatic symptoms did not increase people's risk of heart disease.