Keeping mentally active may help stave off Alzheimer's disease, but once patients are diagnosed with the condition, "brain exercise" may actually speed up cognitive decline, researchers said -- adding that that may not be a bad thing.
Among more than 1,000 older individuals in a large, longitudinal cohort study, scores on a measure of cognitive activity were significantly correlated with the rate of worsening in global cognitive function, according to Robert S. Wilson, PhD, of Rush University in Chicago, and colleagues.
For each one-point increase in cognitive activity scores in Alzheimer's disease patients, the rate of cognitive decline increased 42% (P<0.001), they reported online in Neurology.
But in patients with no cognitive impairment, each point in cognitive activity scores was associated with a 52% reduction in the rate of cognitive decline (P=0.003), confirming previous studies indicating that mental activity reduces the risk of dementia.
"More frequent cognitive activity was related to slower cognitive decline in those without cognitive impairment and more rapid cognitive decline in Alzheimer's disease, with no effect in mild cognitive impairment," Wilson and colleagues wrote.
They argued that such an effect should not be a total surprise.
Other researchers have suggested that mental activity maintains cognitive abilities even as the underlying pathologic burden continues to grow with age.
But, Wilson and colleagues noted, "cognitively active people do develop dementia," presumably when the pathologic burden becomes overwhelming.
"If cognitive activity does somehow allow the brain to tolerate more pathologic changes, those with high premorbid cognitive activity are likely to have a higher pathologic burden than those with low premorbid activity at the time of dementia onset and therefore to experience a more rapidly progressive dementia course," they theorized.
"In effect, these results suggest that the benefit of delaying the initial appearance of cognitive impairment comes at the cost of more rapid dementia progression."
Wilson and colleagues analyzed data from the Chicago Health and Aging Project, an ongoing cohort study that began in 1993. At baseline, participants were 65 or older and were free of cognitive impairment.
The current analysis focused on 1,157 of the participants with 12 years of follow-up. After six years in the study, participants had been tested for cognitive impairment and categorized as cognitively normal, mildly impaired, or having Alzheimer's disease. They were then followed for another six years, undergoing periodic mental status evaluations.
At baseline, participants also rated how often they participated in seven cognitive activities: watching television, listening to the radio, reading newspapers, reading magazines, reading books, playing card or board games, and going to museums.
Cognitive function was evaluated periodically with four brief assessments including the Mini-Mental State Exam, tests of immediate and delayed word recall, and the Symbol Digit Modalities Test.
Wilson and colleagues calculated that the interaction of baseline cognitive activity score with changes in cognitive function scores and time was -0.075 in the Alzheimer's disease patients (SE 0.022), whereas in the participants with no cognitive impairment at follow-up the interaction estimate was 0.029 (SE 0.010).
"These observational data suggest that interventions designed to enhance cognitive plasticity may prove beneficial in compressing the cognitive morbidity of Alzheimer's disease," the researchers wrote.
In other words, "brain exercise" may shorten the period of time in which patients must live with a diagnosis of Alzheimer's disease, as they remain mentally healthy deeper into old age and then decline quickly.
They also noted that, to be effective, cognitive enrichment interventions may need to be initiated before the development of cognitive impairment," since any degree of cognitive deficit probably means an already substantial pathological burden.
Wilson and colleagues cited several limitations to their analysis: the possibility of unmeasured differences between the diagnostic subgroups, the lack of detail in the cognitive function tests used, and a relatively small number of follow-up evaluations.
No commercial funding for the study was reported.
Wilson serves as consulting editor for two other neurology journals and reported several NIH grants. Other authors reported consulting or other relationships with pharmaceutical companies including Pfizer and Eli Lilly.
- Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner