It’s twin power. Identical twins are less likely to die young from unexpected causes, perhaps because of the close social bond between them.

and at the University of Washington in Seattle have examined data on Danish twins born between 1870 and 1900. By comparing the fate of these twins with the general population from that time, they say they have identified a “twin protective effect”, which seems to boost the likelihood of twins surviving into their 60s.

Up until this age, they found that twins are less likely to die unexpectedly. But in later years, genetic factors become more important in determining how likely someone is to die at any given age.

“The effect does appear to be strong,” says Sharrow. For example, the proportion of female twins that live into their early 60s is 10 per cent higher than the average for females.

He believes this is down to the relationship that twins share, which might boost a person’s likelihood of survival because they get material help or emotional support from their twin.

I’ll be there for you

Identical twins seem to benefit from a stronger protective effect than non-identical twins. This could be because they share a deeper bond. “There is some evidence that than non-identical twins,” says Sharrow.

The most protected individuals seemed to be male identical twins, who, unlike female twins, were less likely to succumb to chronic diseases that develop over time. Sharrow thinks this could be because men are generally more likely to have unhealthy lifestyles, doing things like smoking, so a close social bond that pulls them away from bad habits would have more of an effect.

Other studies have shown that people who are or have a larger circles of friends live healthier lives. Some have argued that this might be because healthy people are more likely to find a partner and make friends, but this is unlikely to be the case for twins, because they are twins regardless of their health.

“There is mounting evidence supporting the beneficial health effects of social interaction,” says at University College London. “Even with non-twin siblings, which accounts for about 84 per cent of the total UK population, we can invest in their social relationships to promote their health and well-being.”

But Cable says there may be other explanations for the boosted survival of the twins. “Twins are likely to be born prematurely,” she says. This may mean that any that survived their first days pre-war, when health inequalities were starker, may have been more generally biologically resilient, or had richer parents or a more privileged lifestyle, which are often linked to longer life.

Journal reference: PLOS One, DOI: 10.1371/journal.pone.0154774

Read more: Heal thyself: Trust people

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