WEDNESDAY, Aug. 27 (HealthDay News) -- In their golden years, men and women who remain free of dementia will nonetheless undergo an accelerated drop in key mental skills as much as 15 years before their death, a new study reveals.

Verbal ability, spatial reasoning and perceptual speed are the specific victims of this cognitive decline, which is not, the researchers stressed, a routine part of the aging process.

Instead, this so-called "terminal decline phase" preceding death appears to be the slowly unfolding product of several underlying factors, perhaps including early heart disease, insufficient physical and mental exercise, or even dementia that is so nascent as to be undetectable.

"Before we conducted these analyses, we knew, based on evidence from previous studies, that we might expect acceleration in decline on cognitive abilities before death," said study author Valgeir Thorvaldsson, from the department of psychology at Goteborg University, in Sweden. "[And] our findings clearly showed there to be a pattern of terminal decline, even among relatively healthy individuals, that the brain changes that influence our cognitive abilities in old age occur over a relatively long period of time, even among individuals who remain non-demented until they die."

Thorvaldsson and his colleagues discussed their work in the Aug. 27 online issue of Neurology.

The researchers uncovered evidence of a non-dementia-related dip in mental acuity by tracking the mental skills of 288 Goteberg residents from the age of 70 to their death --which occurred, on average, by age 84.

Over a 30-year period, each male and female participant underwent a maximum of 12 mental health tests, while continuously being evaluated for the possible onset of dementia.

The Swedish team concluded that elderly mental skills do indeed begin to deteriorate independent of both age and dementia. And they expressed some surprise at how much in advance of death such mental decline seems to begin.

Verbal ability, they noted, appeared to start a sharp accelerated decline more than six years prior to death, while a slide in spatial reasoning started to manifest nearly eight years out. However, perceptual speed --or the ability to correctly and quickly compare figures -- was the first to go, beginning to drop off as much as 15 years before death.

The mapping of such occurrences could ultimately help to establish identifiable markers for medical professionals to look for when assessing the possible degeneration of mental health among their elderly patients, the researchers said.

Meanwhile, Dr. James S. Goodwin, director of the Sealy Center of Aging at the University of Texas Medical Branch at Galveston, said the study's principal value is the way in which it drives home the distinction between the normal aging process and the dying process.

"Typically, when you ask the question, how does mental function change with age the older you get, it's easy to mix up people who are merely old with people who are, in fact, dying," he noted. "But the two are not the same."

"And this study," Goodwin added, "illustrates very clearly that there is a certain period before death from so-called natural causes where mental function declines at an accelerating pace. And while most investigators had thought that this kind of decline begins between three to five years before death, this study shows that it, in fact, can be traced back to a starting point that is a lot earlier than previously thought."

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