Twins live longer than the general population read more at here http://www.spinonews.com/index.php/component/k2/item/649

Twins not only have a bestie from birth they also live longer than singletons. According to University of Washington twins have lower mortality rates for both sexes throughout their lifetimes.

The data comes from the Danish Twin Registry, one of the oldest repositories of information about twins.

For men, they found that difference is about 6 percentage points, meaning that if out of 100 boys in the general population, 84 were still alive at age 45, then for twins that number was 90. For women, the peak mortality advantage came in their early 60s, and the difference was about 10 percentage points.

The authors believe their results reflect the benefits of social support, similar to the marriage protection effect. But one question surrounding is marriage protection hypothesis, is whether marriage really makes you healthier, or whether healthier people are just more likely to get married.

David Sharrow, a UW postdoctoral researcher and his co- author, were looking to tune a mortality model using the data from twins. But when they ran the numbers they stumbled upon an unexpected discovery.

Their model separates acute causes of death, such as accidents or behavior-related causes, from natural causes in old age. Female twins only had lower mortality for the earlier, acute causes. Male twins got a bigger overall longevity boost than women because they had lower mortality rates both for acute causes during their early years.

These reflect the immediate and cumulative effects of male twins making healthier choices.  

The lifespan was also extended more for identical rather than fraternal twins, which may reflect the strength of the social bond.

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

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.