Researchers at the University of Utah report in the journal Proceedings of the Royal Society B that women who have twins are more likely to live longer, have more children over their lifetime and have offspring closer together, compared with women who had singletons.
The catch is that these women had twins naturally, in the era well before the advent of contraception or infertility treatments like in-vitro fertilization that now make multiple births relatively common.
The scientists worked with a unique collection of health records known as the Utah Population Database, which includes vital statistics on 1.6 million people who lived in Utah from the early 1800s to the 1970s. The university group divided their data into two population cohorts — those born before and after 1870, when contraceptives started to emerge. In the end the researchers analyzed data on 58,786 non-polygamous women who lived to age 50 or longer.
Women who were born before 1870 and had twins had a 7.6% lower risk of dying each year than women who had singletons. Women born after 1870 who had twins also enjoyed lower mortality, but with only a 3.3% reduction in risk compared with moms of singletons.
Evolutionarily, says the study’s lead author, Ken Smith, director of the Utah Population Database and a professor of family consumer studies at University of Utah, living longer provides a selective advantage. “The argument is that people have to live long enough to bear children and rear them so the offspring live long enough to reach sexual maturity so they in turn can reproduce,” he says. “People who are less able to do that are selected against, and they tend to disappear from the population.”
Mothers of twins, in other words, may be fitter for survival. Having multiple births clearly takes a toll on the mother; previous studies have shown that women who have twins, triplets or other sets of multiples suffer more complications at birth and many long-term effects from carrying more than one child in utero. (Not to mention the headache of raising two babies at once.) But, says Smith, if women are able to survive giving birth to twins, that may indicate that she is endowed with some combination of genetic, physical and physiological characteristics that may contribute to a longer life.
So rather than directly playing a role in longevity, having twins may be a marker of some yet unknown factor that leads to long life. “It’s not that you can go out and have twins in order to live longer,” says Smith. “It’s more that twinning is a reflection of an innate feature that we can’t yet identify that leads to longer life.”
Does this matter to women who may not have twins, or to men? Yes, says Smith. If you’re interested in whether long life is in your genes, you can look into your family tree for any history of twins. “Twinning may be a part of the longevity recipe that people might want to know,” says Smith. Long live twins!