According to Taiwanese researchers, as many as 1 in 14 suicides among Taiwanese youth may have been caused by asthma, a condition that affects about 10 percent of children.
"It points out another negative part of air pollution," said Dr. Wayne Katon, a psychiatrist at the University of Washington in Seattle.
"In a way, suicide is a proxy for a bad effect on the whole society," added Katon, who was not involved in the new research.
Particle pollution - such as smoke, dust and heavy metals — is known to irritate the airways and worsen asthma, and several studies have linked it to heart disease. Why it would make people more likely to kill themselves, however, is unclear.
One possibility is that worsening physical health might push vulnerable people over the edge, especially if they already have chronic disease, said Katon.
He said both studies, published in the American Journal of Psychiatry, highlight the need to treat body and mind as a whole, noting that psychological problems often go hand in hand with bad physical health.
"All patients with chronic illness should be screened for depressive symptoms," he told Reuters Health.
In one study, researchers examined more than 4,000 suicides in seven major cities in South Korea. They found that spikes in particle pollution upped suicide risk by as much as 10 percent.
Overall, Dr. Changsoo Kim from the Yonsei University College of Medicine and colleagues write, about 23 in 100,000 South Koreans commit suicide.
Breaking down the data, those people who had been treated for heart disease in the year before they killed themselves seemed to be more influenced by pollution, with a 19 percent increase in suicide risk.
The researchers say particle pollution is known to cause inflammation in the body. Perhaps, they speculate, this could boost inflammation from the underlying heart disease to aggravate depressive symptoms.
According to Katon, however, "it could be that air pollution worsens patients' perception of their health, which could then cause more psychological problems."
The asthma study, published by Dr. Chian-Jue Kuo of the National Taiwan University, also points to the importance of psychological factors.
Among nearly 163,000 high school students followed over 12 years, wheezing and other asthma symptoms surprisingly turned out not to increase the students' chances of dying from diseases such as cancer and heart problems.
However, during that time, asthma symptoms doubled suicide rates, from about five in 10,000 to one in 1,000.
That means about 1 in 14 suicides among the Taiwanese youth may have been caused by asthma — a condition that, in the U.S., affects about three children in a classroom of 30, the researchers note.
"Suicide is a relatively rare but tragic outcome, and associations with asthma might well reflect more common levels of mental distress," they write. "School staff, clinical staff, and family members should be reminded of the need for awareness of, and prevention measures to improve, mental health in young people, particularly those with more severe and persistent asthma symptoms."