Children growing up in families that are chronically stressed are more likely to have feverish illnesses compared with other children, a new study suggests.

Dr. Mary Caserta at the University of Rochester Medical Center in Rochester, N.Y., and her colleagues looked at the incidence of fever in 169 children ages five to 10.

In general, people develop fevers when their immune systems are trying to fight off infections.

Children from the stressed families also showed a boost in immune system cells that offer the first line of defence against infections, the team reports in the March issue of the Archives of Pediatric and Adolescent Medicine.

It surprised the researchers because theseso-called natural killer cells tend to be weaker when adults are stressed.

"These findings are somewhat surprising to me but also exciting because they show us possible new avenues for improving children's health," Caserta said in a news release.

The researchers said more research is needed to know why the children's immune systems react differently to stress than adults' systems. It may bebecause the children's immune systems are still developing, they suggested.

Researchers gave parents digital thermometers and asked them to record their temperatures, as well as general health and that of their children every week.

Parents also completed surveys about their stress and that of their families, as well as stressful conditions such as violence in the home or neighbourhood,and unemployment.

When the parents' stress level went up by one unit, the rate of general illness among children went up by 11 per cent, and the rate of illness with fever increased by 36 per cent, the researchers said.

The study's authors aim to determine what types of parental and family stresses lead to increased illnesses, so they'll have clues to design interventions that lower stress and help families cope better in the hopes of improving children's health.