Young adults with asthma appear to be at greater risk of becoming obese later in life - and childhood depression may play a role in the connection, according to researchers.

Their study of nearly 600 men and women found that those who had asthma symptoms at the age of 20 were three times more likely than their non-asthmatic peers to become obese by age 40. Also, depression during childhood or adolescence appeared to be a common factor.

All of this suggests that early depression may somehow contribute to the development of both asthma and excessive weight gain, according to Dr. Gregor Hasler of the University Hospital Zurich in Switzerland.

Hasler and his colleagues report the findings in the current issue of the International Journal of Obesity.

A number of studies have suggested that obesity raises the risk of developing asthma, but some researchers have argued that this is not necessarily a one-way relationship. The current findings support this idea by showing that “asthma also may precede obesity,” Hasler told Reuters Health.

And, in fact, the study found no evidence that obesity in young adulthood increased the risk of developing asthma later on. This was an unexpected finding, Hasler said, given that past studies have pointed to obesity as a risk factor for asthma.

Exactly why asthma may contribute to excessive weight gain is not clear. Some asthma medications may cause people to put on extra pounds, the researchers note, but the study lacked detailed information on any treatments asthmatic participants were taking.

People with asthma may also be less likely to exercise - though study participants’ activity levels, reported at two separate times in their 20s, did not explain the connection between asthma and later obesity.

On the other hand, a history of depressive symptoms during childhood or adolescence did explain a large share of the asthma-obesity relationship, the researchers found.

It’s not yet known why the three are linked. One possibility, Hasler speculated, is that early depression is a marker of a stressful family life.

“Since psychological stress early in life is a risk factor for the development of both obesity and asthma,” he said, “it may explain why asthma and obesity co-occur in an individual more frequently than expected by chance.”

It’s also possible that certain genes affect the risks of early depression, asthma and obesity alike, according to the researcher.

For instance, Hasler explained, all three disorders are marked by widespread inflammation in the body, a product of immune system activity. So some genes that help regulate this inflammatory process may also contribute to depression, asthma and obesity.

Most likely, Hasler said, some combination of genes and environment explains the connections between early depression and later asthma and weight gain. He and his colleagues call for more research to unravel the relationships among the three.

SOURCE: International Journal of Obesity, February 21, 2006.