According to a new study, siblings of people with dementia are at an increased risk of shortened life expectancy, even if they themselves are not diagnosed with the condition.
Researchers from the Dornsife College of Letters, Arts and Sciences at the University of Southern California (USC) in collaboration with researchers from the Karolinska Institutet in Sweden, based on data from the Swedish Twin Registry, found that a combination of genetic and environmental factors reduces life expectancy in dementia patients. According to the study published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association, the same combination can also shorten the lives of their siblings, even without dementia.
Dementia affects the ability to remember, think, or make decisions in daily life. The researchers began the study by estimating the average life expectancy of a person after a dementia diagnosis.
„One of the most frequently asked questions when a family member receives a dementia diagnosis is: How much time do we have?“ said lead author Jung Yun Jang. „We believed that answering this question for twins would help patients and their families make decisions about finances and end of life as they cope with this disease which leads to losses over time.“
From a large cohort of over 45,000 Swedish twins, the team examined 90 identical twin pairs and 288 fraternal twin pairs in which one twin had dementia while the other did not.
They found that the dementia diagnosis shortened a patient’s life expectancy by an average of about seven years after diagnosis, a finding that had been confirmed in earlier studies.
However, the study also revealed other interesting findings.
„When dementia is diagnosed in identical twins, both twins have a similarly shortened life expectancy. In fraternal twins, the one who did not develop dementia still has a slightly shortened life expectancy compared to someone who did develop dementia and had no sibling with dementia,“ the researchers stated in a press release.
„We expected a different result. We expected that in twins where one developed dementia and the other did not, the difference in life expectancy would be similar to what we would see in unrelated individuals,“ said Jang.
Researchers believe this is due to the fact that dementia itself is not the sole cause of a shortened lifespan, but rather a combination of shared genes and the environment.
„We assumed that the reason a person with dementia has a shorter life expectancy would be that dementia leads to other conditions that impact mortality. What we are seeing instead is that the increased mortality risk is not solely attributable to dementia itself but to a whole package of other influences that the person brings to their disease,“ Jang added.
„What happens early in life is really important. You may not be able to change that for yourself, but it looks like the message to parents is: Make sure your child is eating healthily, make sure your child is exercising, make sure your child is getting an education. You are actually contributing to that child having a lower risk of developing dementia 75 years later,“ said Margaret Gatz, a study author.