Identical twins live longer, especially boys

Identical twins live longer, possibly because they have a BFF from birth, according to researchers from the University of Washington, Seattle, WA. Furthermore, this effect is greatest in male identical twins, according to results from their recent study, published in the journal PLOS ONE.

"We find that at nearly every age, identical twins survive at higher proportions than fraternal twins, and fraternal twins are a little higher than the general population," said lead author David Sharrow, a UW postdoctoral researcher in aquatic and fishery sciences.

Close social connections may provide this significant health benefit, suggested Sharrow and fellow researchers. For this study, they collected data from the Danish Twin Registry, and assessed 2,932 pairs of same-sex twins who were over 10 years old and born in Denmark between 1870 and 1900. They compared age at death from these twins with data from the general overall Danish population.

In men, the peak mortality benefits of being a twin occurred in their mid-40s, with a difference of about 6 percentage points. That is, if 84 out of 100 boys in the general Danish population were alive at age 45, 90 twins would still be alive. In women, these benefits occurred in their early 60s, with a difference of roughly 10 percentage points.

"Our results lend support to a big body of literature that shows that social relationships are beneficial to health outcomes. There is benefit to having someone who is socially close to you who is looking out for you," said Sharrow. "They may provide material or emotional support that lead to better longevity outcomes."

In addition, researchers used their model to separate acute causes of death from natural causes, and found that female twins only had lower mortality for earlier acute causes. Male twins, on the other hand, enjoyed greater longevity than females because they had lower mortality rates for acute causes in their early years and lower rates for mortality from natural causes after the age of 65.

According to Sharrow, this may be due to the immediate and cumulative effects of male twins making healthier choices.

"Males may partake in more risky behaviors, so men may have more room to benefit from having a protective other—in this case a twin—who can pull them away for those behaviors," Sharrow said.

Longevity was also longer in identical as compared to fraternal twins, possibly due to the strength of the social bond.

"There is some evidence that identical twins are actually closer than fraternal twins," Sharrow said. "If they're even more similar, they may be better able to predict the needs of their twin and care for them."

Sharrow and fellow researchers are currently working on validating these results in other data sets, but, if they do so, the implications and importance of a strong social structure may be valid not only for twins, but singletons as well.

"Research shows that these kinds of social interactions, or social bonds, are important in lots of settings. Most people may not have a twin, but as a society, we may choose to invest in social bonds as a way to promote health and longevity," concluded Sharrow.

This study was funded by the National Institutes of Health's National Institute on Aging.