ANN ARBOR—A man’s health and behavior are more adversely impacted by war and the associated disruption than a woman’s?as evidenced by the dramatic jump in non-combat mortality for Croatian men during the Croatian War of Independence, a new study shows.

It is commonly known that men bear a higher mortality burden from the results of combat, given the composition of most militaries. In the Croatian war, nine times as many men died because of war-related causes. However, a University of Michigan study shows Croatian men also experienced a dramatically greater increase than women in non-combat mortality from both behavioral and internal causes.

The study has implications for understanding male and female psychology, said study author Daniel Kruger, assistant research scientist in the U-M School of Public Health. Kruger co-authored the study with Dr. Randolph Nesse, a researcher in the U-M Institute for Social Research, professor of psychology and psychiatry and director of the Evolution and Human Adaptation Program.

“Conditions of uncertainty where the whole environment is disrupted?tend to make men shift toward riskier behavior,” Kruger said. The difference between male and female mortality rates for behavioral causes of death?accidents, homicides, and suicides?peaked one year after the most intense period of warfare.

Men are also more physiologically susceptible to stressors in the environment around them, Kruger said. That’s because the male body invests more in competition than it does in preserving and maintaining itself, because males have historically faced greater competition for mates. On the other hand, he said, females invest more in self- preservation for the sake of raising and caring for offspring.

The study infers that the rise in deaths during and after the war, which lasted from 1991-1995, occurred because men have evolved to have riskier behavior and riskier physiological responses than women when their surroundings are in turmoil, Kruger said.

Data collection is usually not a high priority for the health infrastructure during warfare. In this case, however, reliable high quality mortality data is available from the World Health Organization’s mortality database.

Kruger and Nesse analyzed data from 1998 to 2002 in 10-year age groups. In the period following the war, the ratio of male deaths to female deaths was as high as 4.5 to 1 in the 35-44 year old age group, the study showed. Usually, the peak sex difference in mortality happens in the younger age group of 25-34, Kruger said. But in the decade after the war, men who underwent those experiences may still have been living with the shadow of them, he said.

Under normal circumstances, for every Croatian woman who dies between the ages of 15-34, three men of the same age group will die. Earlier studies by Kruger and Nesse have shown that this ratio holds true across modern nations. “In many developed nations being male is the largest demographic risk factor for early mortality,” Kruger said.

The entire study appears in the latest issue of Psychological Topics.

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