Twins live longer than the general population, according to an analysis of almost 3,000 pairs of twins published in the journal PLOS ONE.
Identical twins had the biggest advantage, researchers at the University of Washington found. The reason, they suggested, was the social support that came with having a twin.
The study looked at Danish twins born between 1870 and 1900 who all survived past the age of 10, using data from the Danish Twin Registry.
Lead author David Sharrow, a postdoctoral researcher in aquatic and fishery sciences at the University of Washington, said: ‘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.’
The strongest benefit for male twins came in their mid-40s, when they had a six percentage point advantage over non-twins. That is, if 84 out of 100 men were still alive aged 45, then for twins that number would be 90. For women the benefit was highest when they were in their 60s. The difference was 10 percentage points.
‘Our results lend support to a big body of literature that shows that social relationships are beneficial to health outcomes,’ said Sharrow.
The study separated acute causes of death (ie, accidental or behaviour-related deaths) from deaths of natural causes. Female twins only had lower mortality for the first category. Male twins had a longevity advantage for both causes of death.
Sharrow suggested the difference was down to the cumulative effect of male twins making healthier choices thanks to the support of a significant other.
‘Males may partake in more risky behaviours, 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 behaviours,’ he said.
This interesting population-based study suggests there appears to be a survival advantage to being a twin.
Specifically it found that monozygotic twins (twins that result from a single egg, fertilised by a single sperm with the subsequent cell mass splitting off into two and are hence identical) live longer than dizygotic twins (twins resulting from two eggs being fertilised and are hence non-identical) who, in turn, live longer than individuals who are not twins.
Any population-based study usually establishes correlation and not causation, and in this case we have no direct data to support why being a twin appears to be advantageous. It is possible that the close bond between twins manifests itself in health habits that are perpetuated due to the mutual support available, in the manner of gym partners who encourage each other through arduous workouts. There may be a genetic basis as well, with twins inheriting hardier genes, manifestly more so in monozygotic twins who genetically can be almost identical. Socioeconomic factors may also play a role, along with many other possible factors.
Whether this study is applicable to more heterogenous populations remains to be seen. Denmark is relatively homogenous — about 90 per cent of the population are of Danish descent — something not necessarily reflected in the ethnic make-up of other European countries.