Why Women Live Longer Than Men

A new study that examined the records of 140,600 individuals using data from the Utah Population Database (UPDB) found that lowered birth rates across time have contributed to women living longer lives. The study, led by Elisabeth Bolund of Uppsala University in Sweden, mapped years lived for both men and women who were born between 1820 and 1919 in Utah. Over that decade, women went from having 8.5 to 4.2 children. This corresponded with an average adult lifespan increase of 12 percent for women, suggesting that the reduced stress of reproduction and its associated costs allowed women to live longer. For men, who don't physically bear as much of the cost of child birth as women—if any—lower birth rates only amounted to a 2 percent lifespan increase.

Bolund's findings support previous research that has shown women haven't always outlived men—and the fact that, in some countries, they still don't, according to data obtained by Bolund and her team of researchers from the Population Reference Bureau. Bolund's study clearly points to how lifespan as related to sex has changed over time. According to the dataset that Bolund pulled from the UPDB—a multi-generational database that has info on eight million individuals from the late 18th century to the present (due initially to the Mormon Church's penchant for record keeping)—the lifespan for women increased with each cohort. From 1820 to 1844, Utah men outlived women by one year. By 1845, as birth rates decreased slightly, women caught up. By 1870, women outlived men by two years and by 1895, four.

"We don't claim that birth rate explains everything," Bolund explained over the phone, "but it can explain part of the variation in sex differences in lifespan. It's only one of the reasons why today women live longer than men. Fertility explains some of the variation, but not all of it."

To control for various factors, like death during childbirth, the researchers also evaluated the lifespans of individuals born from 1820 to 1920 by mapping how many years an individual lived after age 55, or the end of the reproduction period, against the number of children an individual had. The graph of the results is illuminating: While men's lifespans weren't affected by the number of kids they fathered—the highest being 65 children (#polygamy)—women's lifespans drastically decreased after giving birth to more than four children. "There was no relationship whatsoever between how many children a man fathered and his subsequent lifespan after age 55, even at the extremes," Bolund said. On average, women who gave birth to 15 children or more lived six years shorter than women who only had one child.

But unfortunately, we'll have to wait a while until we can confirm what effect the efforts of reproduction still have an lifespan. With advances in modern medicine making childbirth a less stressful event now than it was in the 1800s, the researchers can't say, based on this study, if having less kids means you'll live longer. "If you want to look at lifespan, you have to wait until all the individuals in your study have passed away," Bolund said. "For humans, since our lifespan is so long, we cannot really look at these questions for individuals born after 1920. It could be possible that you wouldn't see these effects in women who are of reproductive age now."