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"We found accelerated changes in people's mental skills that indicated a terminal decline phase years before death," Valgeir Thorvaldsson, of Goteborg University, Sweden, noted in a statement issued by the Academy.
The start of the terminal mental decline is different for various cognitive abilities, Thorvaldsson and colleagues found.
For example, perceptual speed - a measure of how quickly people can compare figures - begins to decline nearly 15 years before death, whereas spatial ability starts its downward trend nearly 8 years before death. An older person's verbal ability starts declining about 6 to 7 years before death.
"Based on previous studies, we expected to see this type of pattern of change to start about 4 to 6 years before death," Thorvaldsson told Reuters Health. "Interestingly, however, our data showed that the terminal decline onset was as early as 15 years before death. This varies though across individuals and abilities, but it is much earlier than we had expected," the researcher noted.
Other health factors to consider
A number of factors may explain this terminal decline in mental skills. "Cardiovascular conditions such as heart disease or dementia that is too early to be detected could be factors," Thorvaldsson pointed out in the statement. "Increased health problems and frailty in old age often lead to inactivity, and this lack of exercise and mental stimulation could accelerate mental decline."
The study findings also suggest older people remain stable in their verbal abilities unless they are burdened by diseases that also increase their risk of death. "A change in verbal ability might therefore be considered a critical marker for degeneration in health in older people," Thorvaldsson said.
The findings are based on a study of 288 people without dementia who were followed from age 70 to death, which occurred, on average, at age 84. The participants' mental skills were measured up to 12 times over a period of 30 years.
"The sample consisted of a group of initially healthy individuals that never received a diagnosis of dementia over their lifetime. These findings therefore indicate that, even among healthy individuals, the brain changes that affect our cognitive abilities operate over a long period of time," Thorvaldsson told Reuters Health. - (Megan Rauscher/Reuters Health)
SOURCE: Neurology, online August 27, 2008.
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