The researchers measured the perceived age of the twins from photographs and physical and cognitive tests, along with the use of the length of leucocyte telomeres, which are a molecular biomarker of aging.
A telomere that is of a shorter length usually signifies that a person will age faster.
These shorter-length telomeres have also been linked with larger numbers of diseases in individuals, when compared to longer-length telomeres in other individuals.
In the study, the twin that was perceived as being younger than the other sibling had longer telomeres.
As of January 2008, 675 of the subjects of the 1,826 total (37%) had died over a seven-year period.
The twin that was ranked as looking younger than the other twin tended to outlive their older-looking sibling.
The researchers found that the perceived age of each twin was significantly associated with survival and life span. Extraneous factors such as chronological age, sex, professional career, and the general environment did not change the results.
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