Sharp Verbal and Other Cognitive Declines Signal Impending Death

By Michael Smith
GOTEBORG, Sweden, 28 aug 2008 -- Even in the absence of frank dementia, cognitive abilities begin to drop off sharply several years before death, researchers here said.
The so-called "terminal decline" in verbal ability begins to occur on average 6.6 years before death, according to Valgeir Thorvaldsson, M.Sc., of Goteborg University and colleagues.
Declines in spatial ability and perceptual speed begin on average 7.8 years and 14.8 years before death, respectively, they reported online in Neurology ahead of the Sept. 16 issue.
"There is substantial acceleration in cognitive decline many years prior to death among individuals without dementia, the researchers concluded, and the "time of onset and rate of terminal decline vary considerably across cognitive abilities."
The terminal decline is an accelerated change in abilities associated with mortality and differs from the changes associated with simple aging, the researchers said.
Thorvaldsson said the terminal decline in mental skills may be associated with several possible factors.
"Cardiovascular conditions such as heart disease or dementia that is too early to be detected could be factors," he said. "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 finding emerged from a 30-year study of people in this Swedish city, who were born in 1901 and 1902. They were enrolled at the age of 70 and followed until death, with up to 12 measurements of verbal, spatial, and perceptual speed abilities.
The researchers analyzed the results of the measurements in relation to two time-dependent changes -- age and proximity to death.
The study found that the so-called "age slopes" -- the average annual changes in the three domains relative to age:
Did not change significantly for verbal ability until the terminal decline began 6.6 years before death.
Declined by 0.031 standard deviations for spatial ability until the terminal decline started at 7.83 years before death, which was significant at P<0.05.
Declined by 0.022 standard deviations for perceptual speed until the terminal decline started at 14.83 years before death, which was significant at P<0.05.
On the other hand, once the terminal decline started, the rate of change was significantly greater (at P<0.001) for all domains. The slope of the post-change curve was:
13 times larger than the age slope for verbal ability
Almost twice as large as the age slope for spatial ability
Twice as large as the age slope for perceptual speed
One implication of the findings is that verbal ability, which remains almost constant until the terminal decline starts, might be a sign of worsening health, Thorvaldsson said.
"People remain stable in their verbal abilities unless they are experiencing disease processes that also increase their mortality risk," he said. "A change in verbal ability might therefore be considered a critical marker for degeneration in health in older people."
The researchers cautioned that the findings might not generalize to other birth cohorts, whose onset and rate of terminal decline might differ. They added that test-retest effects might be present.
The study was supported by Swedish Brain Power and the Swedish Council for Working Life and Social Research. The researchers made no disclosures.
Primary source: NeurologySource reference:Thorvaldsson V, et al "Onset of terminal decline in cognitive abilities in individuals without dementia" Neurology 2008; 71: 1-1.