Study Finds Dementia in a Twin May Shorten Sibling’s Lifespan

As reported in HealthDay News, a study by U.S. and Swedish researchers involving twins suggests that if you have a sibling who develops dementia, this might lead to a shorter lifespan for you. This is true even if you do not develop dementia yourself. The lead study author, Jung Yun Jang, said this finding came as a surprise because “We expected that, in twins where one developed dementia and the other did not, the difference in life span would be just like we see in unrelated people.” The initial object of the study, funded by the National Institutes of Health, was to assess typical life span after a dementia diagnosis, which is about seven years. The study involved 90 pairs of identical twins and 288 pairs of fraternal twins, all from a 40-year database out of Sweden known as the Swedish Twin Registry. In all sets of twins used in the study, one twin had developed dementia while the other had not. In this study, life span post-diagnosis was roughly similar for the identical twins where one is diagnosed with dementia, but among fraternal twins, when one is diagnosed with dementia, the twin unaffected by dementia had a slightly shortened life span, compared to people who have no sibling with dementia. The study team said it’s not clear why simply having a sibling with dementia would lower a person’s life span, although the shared environment siblings grow up in could play a role. For example, both might have had unhealthy dietary or other habits in childhood that could lead to a shared risk for heart disease decades later, which is known to raise dementia risk.