A crossword a day keeps Alzheimer's away...

Alzheimer’s disease is the leading cause of dementia in older persons yet few risk factors have been identified. The study being discussed, performed by Dr. Robert S. Wilson and colleagues, intends to test the hypothesis that frequent participation in cognitive activities is associated with a reduced risk of AD. The forthcoming information is extracted from Wilson’s methods and findings. It included a total of 801 older (65+ years) Catholic nuns, priests, and brothers without dementia at enrollment, recruited from 40 groups across the United States. Longitudinal observations and evaluations were made between January 1994 and July 2001 with a mean follow-up of 4.5 years. Out of the 801 participants, follow-up information on AD was available for only 733 due to incidents such as death with other participants. Each participant was evaluated annually by examiners with a mean of 5.5 evaluations per person. Evaluations included medical history, neurological examination, assessment of cognitive function, and review of brain scan when available.

Cognitive activity is very hard to define considering people come from different cultural and socioeconomic backgrounds. Respondents therefore rated their current and past frequencies in activities that involved seeking or processing information. The participants were asked how much time each spent doing certain activities including: watching television, listening to radio, reading newspapers, reading magazines, reading books, playing games such as cards, checkers, crosswords, or other puzzles, and going to museums. Frequency was rated on a 5 point scale, 5 being everyday, and 1 being one time or less a year.

A scale from 1.57 to 4.71 (mean, 3.57) was observed as a measurement of cognitive activity with higher scores indicating more frequent activity. The results showed that during an average of 4.5 years follow-up, 111 participants developed Alzheimer’s disease. From the 1.57 – 4.71 cognitive activity scale, a 1 point increase was associated with a 33% reduction in risk of AD. Of the 111, 101 met NINCDS/ADRDA criteria for probable AD and 10 for possible AD (because of cognitive impairment due to stroke in 5 and to Parkinson disease in 5). Table 1 demonstrates baseline characteristics of those participants who did and did not develop AD.

So as already stated the relative risk (RR) of developing AD decreased by 33% for each 1-point increase in the composite measure of cognitive activity; Table 2 illustrates the RR under certain criteria.

The RR is set to change from a baseline of 1, for example, as the asterisk below the table points out, a 1 unit increase in cognitive activity score will show a .33 decrease in RR (i.e. decrease from baseline 1 to 0.67 = .33) and for every 1 year increase in age the RR increases by .14. So as an example for the participants, compared with a person with activity frequency at the 10^th percentile (score = 2.86), the RR of AD was reduced by 28% in a person whose activity was in the 50^th percentile (score = 3.71) and by 47% in a person whose activity was in the 90^thpercentile (score = 4.29). Education was not related to disease risk in this model (i.e. change from baseline 1 to 1.02 was negligible). The article makes other comparisons and accounts for variables that needed to be addressed such as early onset AD, depression, physical activity, and the presence of the ApoE epsilon4 allele which is a known risk factor for AD.

Along with the study, cognitive activity was compared to the change in cognitive function starting at the manifestation of AD in the patients that had developed it. The analysis used the global measure of cognition, which ranged from -1.765 to 1.374 at baseline, with higher scores indicating better function. Each point of cognitive activity score was associated with 0.128 units in the global cognitive score. On average, the global cognitive score declined 0.043 units per year of evaluation and this rate decreased by 0.020 units (~47%) for each 1-point increase in cognitive activity score. Table 3 demonstrates the results.

So basically on average, a person with activity frequency at the 10^th percentile declined 0.046 units per year in global cognition; the rate was reduced by 0.014 units (~30%) for an activity frequency score at the 50^th percentile and by 0.026 units (~60%) for an activity frequency score at the 90^th percentile. The table also shows correlations between cognitive activity and other domains of cognition. So on average performance declined in each domain, as shown by the terms for time. Every 1-unit increase in cognitive activity however showed a decrease in the decline rate as illustrated by the “cognitive activity x time” portions of the table. As is exemplified cognitive activity was associated with lower rates of decline in working memory and perceptual speed. The change in semantic memory and visuospatial ability was not significantly related to cognitive activity.

The study showed a correlation between cognitive activity and development of AD yet the association between the two is still uncertain. As directly stated in the article, one hypothesis is that cognitive activity is protective. One version of this hypothesis is that with repetition some cognitive skills become more efficient and less vulnerable to disruption by AD pathology. Alternatively, frequent cognitive activity may strengthen processing skills such as working memory and perceptual speed, which may help to compensate for age-related decline in other cognitive systems. So if cognitive activity is protective, reduced cognitive activity should be an early sign of disease.

Reference:

Wilson, Robert S., Carlos F. Mendes De Leon, Lisa L. Barnes, Julie A. Schneider, Julia A. Bienias, Denis A. Evans, and David A. Bennett. "Participation in Cognitively Stimulating Activities and Risk of Incident Alzheimer Disease." The Journal of the American Medical Association 287 (2002): 742-48. JAMA. Web.