In the years between adolescence and adulthood, about three men die for every woman

University of MichiganMay 25 2004

In the years at the dangerous border between adolescence and adulthood, about three men die for every woman, according to a new University of Michigan study of the ratio of male to female mortality rates in 20 nations, including the United States.

The study, selected as a "hot topic talk" to be presented May 28 at the annual meeting of the American Psychological Society, also appears in the current issue of the journal Evolutionary Psychology.

"Being male is now the single largest demographic risk factor for early mortality in developed countries," said Daniel Kruger, lead author of the study and a social psychologist at the U-M Institute for Social Research (ISR), the world's largest academic survey and research organization. ISR researcher Randolph Nesse, professor of psychiatry at the U-M Medical School, is the co-author of the study.

Funding for the analysis was provided by the National Institute of Mental Health.

Kruger and Nesse used data from the National Center for Health Statistics, the World Health Organization and the Human Mortality Database to examine the difference between male and female mortality rates for 11 leading causes of death across age groups in the United States. They also studied the same mortality rates over the course of the lifespan in 20 countries, and over the past 70 years in five countries: the United States, the United Kingdom, Sweden, France and Japan.

In the United States, they found that in the year 2000 males had higher mortality rates than females for all 11 causes of death across the lifespan. "The magnitude of the sex difference is most starkly summarized by the numbers of deaths before age 50," Kruger said. "For every 10 premature female deaths, 16 men died prematurely."

The overall ratio of U.S. male to female mortality rates increased sharply at adolescence, peaking at 2.94 from ages 20 to 24 and slowly decreasing to 1.46 from ages 75 to 79.

The highest male-female mortality ratio for a specific cause was 9.03 for suicide from ages 75 to 79, meaning that nine men that age killed themselves for every woman who did. The next highest male-female mortality ratios were for homicide (5.72) and non-automobile accidents (4.91) from ages 20 to 24.

The researchers also compared cross-national data from 20 countries, finding higher male than female mortality for nearly all ages with a substantial peak at sexual maturity.

"This is the stage of life when males of many species engage in high levels of risk-taking and competitive displays that tend to increase their reproductive success," Kruger said. "The higher degree of mating competition among males is the evolutionary reason why females live longer on average in most animal species."

Finally, Kruger and Nesse analyzed historical patterns of age-related male-female mortality starting in 1930 in the United Kingdom, the United States and Sweden, and beginning after World War II in France and Japan. In all five cultures, they found two pronounced peaks in male to female mortality ratios, both increasing markedly in the mid-20th century. The first peak is sharp and centers at the age of sexual maturity, while the second, more rounded peak reaches a maximum around age 65.

"The results confirm our expectations that evolved sex differences interact with aspects of current environments and cultures to result in considerably higher mortality rates for men than for women, especially in early adulthood and especially for external causes of death," Kruger said.

"If male mortality rates could be reduced to those for females, one-third of all male deaths under age 50 would be eliminated. Since these deaths result from complex interactions of sex, behavior and culture, simple solutions are unlikely. Still, the general tendency for males to take greater risks ties together many preventable causes of death and is a worthy focus for interventions."