May 11, 2006 -- Women generally outlive men, and researchers are exploring the reasons why.
Evolution may play a role, researchers note in the journal Human Nature. But other factors also work in women's favor, and it's possible for anyone -- male or female -- to work toward a longer, healthier life.
First, take a look at the latest snapshot of U.S. life expectancy. In 2004, the most recent year for which such statistics are available, life expectancy from birth was 77.9 years. In 2004, life expectancy for U.S. women was 5.2 years longer than men.
Women don't just outlive men in the U.S. In April, researchers in England predicted that 2006 may be the year in which women outlive men all over the world, even in the world's poorest countries.
Vying for Attention
Here's the short version of the study, published in Human Nature: Male animals often have to compete for female attention -- witness the male peacock's showy tail and the male moose's battle-ready antlers; vying against other suitors can be risky.
The University of Michigan's Daniel Kruger, PhD, and Randolph Nesse, MD, wrote the paper. They argue that men are much more likely than women to engage in risky and sometimes violent behavior, ultimately raising men's death rate.
More men than women die in car accidents, other types of accidents, homicides, and suicides, the researchers note. They add that in the U.S., the gender gap in death rates peaks in young adulthood and is mainly due to behavior.
Kruger and Nesse took a big-picture look at how evolution may contribute to male-female death rates.
They don't claim that all men engage in risky behavior to impress women, or that all women look at daredevils and think, "I'd like him to father my children." They also don't dismiss women's health risks.
However, Kruger and Nesse note that men, particularly those experiencing uncertainty or deprivation, "may develop riskier life strategies, leading to higher mortality rates." Of course, many men may not act that way when facing uncertainty or harsh conditions.
The male-female gap in death rates may be a sign of male-male competition in a society, the researchers also suggest.
"Up until very recently in human terms, life expectancy for men was greater than for women," Carol J. Hogue, PhD, MPH, tells WebMD.
Hogue is a professor of maternal and child health and of epidemiology at Emory University's Rollins School of Public Health.
"I'm not talking about elderly people and whether the next year they're going to be alive," she explains. "I'm talking about the average number of years lived for a baby born. That's life expectancy at birth." Kruger and Nesse's study tracked death rates, not life expectancy from birth.
Why did women overtake men in life expectancy? "The difference is maternal mortality," Hogue says. Maternal mortality includes women's deaths during or associated with childbirth.
Maternal mortality improved in the developed world in the early 20th century and followed suit in most of the developing world, "although there are still areas in the developing world that have very high rates of maternal mortality," Hogue says.
It's "certainly true," Hogue says, that "males are much more at risk of violent death and associated with taking risks." She says "that may be part of the explanation as to why life expectancy at birth is now better for women than men."
"The major killer in early life for women was maternal mortality, and that has been tamed considerably, whereas the major killer for men is violence and accidents, and that has not gone down as dramatically as childbirth deaths have gone down," Hogue says.
Women shouldn't take their longer life expectancy for granted. The 2004 gender gap in U.S. life expectancy was the smallest it's been since 1946. If women continue to adopt unhealthy habits like smoking, the gap may narrow further.
"Also, now that obesity is such a major player in life expectancy, I don't think we know what impact that's going to have," Hogue says. She adds that some scientists have theorized that women may have greater genetic protection against premature death.
Boosting Your Life Expectancy
Men and women can take steps toward a longer, healthier life.
"You can change your life expectancy if you start today exercising, eating right, reducing stress through one or another stress-reduction methods like meditation, avoiding risky behavior, wearing your seatbelt, not cutting people off in traffic," Hogue says.
"In other words, you have your own destiny in your own hands, up to a point," she says.