A new study reinforces the growing body of evidence on health disparities between men and women and may possibly shed light on why socially isolated men are more vulnerable to disease and death than isolated women.

The study by the Universities of Chicago and Wisconsin, has found that socially isolated female rats that experience stress have a much stronger response to infection than similarly isolated and stressed males.

The researchers suggest that the females strong response may stem from the demands motherhood makes on them.

Lead researcher Gretchen L. Hermes from the the University of Chicago, says previous studies have already established a link between stress and immune function, but their study looked at the long-lasting effect that three months of isolation which would be the equivalent of chronic social stress, and one 30-minute episode of acute physical stress had on the inflammatory response, the body’s innate immune response to bacteria, viruses, and parasites.

The authors say they found that a full two to three weeks after being subjected to isolation and the acute physical stress, male rats showed a markedly slower healing response when injected with a foreign body compared to female rats.

Senior study author Martha McClintock, director of the Institute for Mind and Biology at the University of Chicago, says the finding is significant because the inflammatory response is an important immune response involved in many diseases, including heart disease, cancer, and infectious disease.

In the experiment Norway rats were used because they are a particularly social species of rats which live in large colonies of closely spaced burrows with cooperative grooming, feeding and rearing of offspring.

As Hermes says they are not just any old rat but are particularly gregarious, especially the females of the species and removing them from their social context produces a profound effect.

The study covered a three month period, a significant portion of the rat’s life span, and showed the lasting effects of an acute stressor superimposed on the chronic social condition of isolation, says Hermes, and was a more like a real ‘life’ study.

The research complements other studies which have found that in times of stress, rats are more likely to give birth to female offspring than male offspring, which suggests says McClintock that male offspring are less likely to survive under stressful circumstances.

The study also fits with human studies, which found that socially isolated men are more likely to become ill and die sooner than similarly isolated women.

The authors speculate that the reason females heal more quickly than males under stress may be a protection feature that evolved in the context of females protecting their offspring.

The team also say another possibility is that male and females experience stress differently.

The study is published in the February issue of the American Journal of Physiology.