Identical twins live longer

Identical twins live longer than other people, a new study shows. And for the rest of us, there’s marriage.

A pair of researchers in the US compared Danish identical twins’ lifespans to non-identical twins and the general population. They found that at every age, identical twins win out when it comes to survival rates.

The average lifespan increase for identical twins, according to the research, is similar to the increase that’s predicted by people who are married, suggesting that companionship could be one key to a longer life.

To produce the findings, published in the journal PLOS One, David Sharrow and James Anderson at the University of Washington in the US used data from the Danish Twin Registry, a comprehensive record of the country’s twins, identical and non-identical, born in Denmark between 1870 and 1900.

The time period was chosen, the paper states, because “all twins born in the 1870-1900 cohort are now deceased and thus the length of their life is known”.

This was compared with data from the Human Mortality Database, which records deaths in Denmark, for the general population born between 1870 and 1900.

Sharrow and Anderson then applied a detailed “vitality model” to account for variance in the demographics, including historical and social factors.

The research divides cause of death into two groups: intrinsic and extrinsic factors, where “intrinsic” refers to the deterioration of health and general ageing, and “extrinsic” is an environmental or external cause of death.

When it came to external causes of death, twins had a higher survival rate at almost every age, and across both sexes, than other people. Identical twins scored the highest.

According to the findings, male identical twins are more likely to survive external factors until age 70, when the advantage of being a twin appears to reverse.

Interestingly, in males of older ages, survival rates are higher among identical twins, suggesting their ageing and deterioration occurs at a slower rate than non-identical twins, and the rest of the population.

The paper states that a plausible explanation for this survival among older males could be “that the social closeness of [identical] twins over [non-identical] twins may encourage cumulative health behaviours throughout life (e.g. avoidance of smoking) that translate to higher survival portions at advanced ages”.

The research compares its findings to ‘marriage protection’ – a statistics-based phenomenon that suggests “married adults are generally healthier and at lower mortality risk than unmarried adults”. According to the research, marriage protection occurs at a similar rate to the ‘protection’ of being an identical twin.

The researchers point out that the marriage protection phenomenon is potentially flawed because healthier people may be more likely to get married.

But in the case of twins, there’s no self-selection to counter the findings.