The average survival time for people diagnosed with dementia is about four and a half years, with age, sex, and existing disability all having an effect on life expectancy, according to a new research.
Researchers from the University of Cambridge also found that those diagnosed before the age of 70 typically live for a decade or longer.
In order to learn more about survival characteristics among patients with Alzheimer's disease or other dementias, the research team followed 13,000 people who were aged 65 and older for 14 years.
They recorder the factors known to have an association with mortality, such as age, sex and marital status, accommodation type, education level, social class, self-reported health and disability.
During the follow-up, 438 of the study participants developed dementia and 356 of these people died, reports BMJ.
Overall, women lived slightly longer than men after a diagnosis of dementia, around 4.6 years vs. 4.1 years, and frailer patients died sooner than healthier ones.
There was nearly seven years difference in survival between the youngest and the oldest people with dementia - 10.7 years for those aged 65-69 and 3.8 years for those aged 90 or over.
But being married, living at home, and even degree of mental decline were not found to have a big impact on survival, the researchers found.
They also showed that those with higher education had slightly shorter survival than those with lower education, but this did not reach statistical significance.
The authors pointed out that being aware of the factors that influence the length of survival after onset of dementia is important.
They added that their findings would be of value to patients, carers, service providers and policy-makers.
The study is published in the British Medical Journal.