Diabetes' Effect on Cognitive Function Spans Age Groups

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Diabetes' Effect on Cognitive Function Spans Age Groups
January 05, 2009
By Charles Bankhead
MedPage Today

EDMONTON, Alberta, Jan. 5 -- Cognitive functioning for adults with diabetes begins slowing down early in the disease process and persists for decades, suggested a longitudinal study.
Action Points

* Explain to patients that this study suggested that diabetes adversely affects specific aspects of cognitive functioning.

* Point out that the adverse effects of diabetes appeared to persist across age groups.

* Note that the findings came from an observational study, which cannot prove that diabetes causes cognitive dysfunction.

Compared with nondiabetic adults, those with diabetes performed significantly worse on tests of executive functioning and speed of mental processing, Roger A. Dixon, Ph.D., of the University of Alberta, and colleagues reported in the January issue of Neuropsychology.

The differences were apparent in baseline assessments and remained significant all the way to age 90.

Current trends in diabetes epidemiology suggest the findings have potentially major implications for aging populations, according to the authors.

"Given the modern Western lifestyle, associated health risks, and growing populations of older adults, type 2 diabetes will likely increase as a common aging-related challenge to neurobiological and cognitive health," they said.

"Future studies examining longitudinal trends in neuropsychological sequelae of diabetes will help determine whether different patterns of cognitive decline occur across both health condition . . . and neuropsychological domain."

Few studies had examined the nature of diabetes' adverse effects on cognitive function (broad versus specific) or whether the effects differ across age groups, the authors noted.

Building on an existing database, Dr. Dixon and colleagues examined cognitive functioning in a cohort of 465 participants ages 53 to 90 at enrollment. At baseline, the participants were relatively healthy and "generally cognitively intact," and 41 had type 2 diabetes.

Participants were followed at three-year intervals, and assessments encompassed physical and mental health.

Assessments of cognitive functioning comprised episodic memory, semantic memory, verbal fluency, executive functioning, and neurocognitive speed. Each parameter was evaluated by multiple neurocognitive tests.

The diabetic participants performed significantly worse on two of four tests of executive functioning (P=0.013, P=0.003) and had a trend toward worse performance on a third test (P=0.072). Additionally, individuals with diabetes had significantly worse scores on all three tests of semantic speed (P=0.038 to P=0.008).

In a separate analysis, the investigators examined test scores by age, dividing the cohort into age groups of 70 and younger versus older than 70. The older study participants had significantly worse scores on all but four of the 20 individual tests, which spanned all domains of cognitive functioning.

The second analysis also corroborated the first by showing worse scores among diabetic versus nondiabetic participants. On the basis of the comparison of the age-stratified groups, the authors speculated that diabetes might exacerbate age-related effects on cognitive functioning.

The authors noted that the studies were limited by the population studied and were not necessarily representative of the general population. In addition, the diagnosis of type 2 diabetes was not based upon precise biological information.