Atheroslerosis, cognitive impairment, and depression in old age.
Vinkers, D.J.Citation
Vinkers, D. J. (2005, September 15). Atheroslerosis, cognitive impairment, and depression in old age. Retrieved from https://hdl.handle.net/1887/3386
Version: Corrected Publisher’s Version
License: Licence agreement concerning inclusion of doctoral thesis in theInstitutional Repository of the University of Leiden Downloaded from: https://hdl.handle.net/1887/3386
Chapter 2
The linear mixed model
Vinkers DJ, Gussekloo J, W estendorp RG. Leisure activities and the risk of dementia.
Chapter 2
16
Introduction
Participation in cognitive leisure activities may reduce the risk of dementia in subjects above 75 years1. We examined the relation between cognitive leisure activities and cognitive decline in subjects above 85 years within the Leiden 85-plus Study2. The association of cognitive leisure activities and cognitive function was analyses with linear mixed models.
M ethods
Mixed modelsWe analysed the association of cognitive leisure activities and cognitive function with linear mixed models adjusted for sex, level of education, and level of income. M ixed models use all available data during follow-up, can properly account for correlation between repeated measurements, and can handle missing data more appropriately than traditional models. They allow also for the use of time-independent and time-dependent covariates. The flexibility of mixed models makes them the preferred choice for the analysis of repeated-measures data3. Cognitive function was entered in the models using the annual obtained testscores. All models included the number of cognitive leisure activities at baseline, time, and the interaction of the number of cognitive leisure activities at baseline and time. The estimate for "number of cognitive leisure activities at baseline" reflects the cross-sectional impact of cognitive leisure activities on cognitive function. The estimate for "time" reflects the annual change of cognitive function. The estimate for "interaction" of the number of cognitive leisure activities at baseline and time reflects the additional annual impact of cognitive leisure activities on cognitive function per cognitive leisure activity extra per week. All models were adjusted for sex, level of education, and level of income.
Other measurements
Cognitive leisure activities included participating in organized work and social activities, reading, puzzling, handicrafting, and visiting a restaurant or theatre. All participants were visited annually for measurements of global cognitive function (M ini-M ental State Examination), attention (Stroop Test), processing speed (Letter Digit Coding Test), immediate recall memory (Word Learning Test Immediate Recall) and delayed recall memory (Word Learning Test Delayed Recall).
Resul
ts and discussion
The linear mixed model
17 Table 2.1 shows that participation in cognitive leisure activities is associated with a reduced decline of global cognitive function, a reduced decline of attention, and a reduced decline of processing speed. In contrast, cognitive leisure activities did not preserve the decline of immediate and delayed recall memory. These findings are in line with the effects of cognitive training intervention being stronger for speed and reasoning than memory4.
Table 2.1 Effects of cognitive leisure activity on cognitive decline in subjects aged 85 years.
Cognitive Test Cross-sectional effect Additional annual effect
Estimate (± SE) P value Estimate (± SE) P value Global cognitive function (points) -0.04 ± 0.06 .49 0.06 ± 0.02 .01
Attention (seconds) -0.04 ± 0.50 .93 -0.31 ± 0.07 .01
Processing speed (digits) 0.32 ± 0.15 .03 0.06 ± 0.03 .04
Immediate Memory (words) 0.13 ± 0.10 .21 -0.01 ± 0.03 .64
Delayed Memory (words) 0.03 ± 0.05 .53 0.01 ± 0.01 .42
At baseline, all 102 participants had a Mini-Mental State Examination score of 29 points and a 15-item Geriatric Depression Scale score < 4 points. Rates of decline were estimated by linear mixed models adjusted for sex, level of education, and level of income. Effect of cognitive leisure activity is expressed as the difference in mean annual rate of decline for one cognitive leisure activity per week extra. Cognitive leisure activity included participating in organized work and social activities, reading, puzzling, handicrafting, and visiting a restaurant or theatre (Median: 14 activities per week, Interquartile Range: 8 - 15 activities per week).
References
1 Verghese J, Lipton RB, Katz MJ, et al. Leisure activities and the risk of dementia in the elderly. N Engl J Med 2003; 348: 2508-16.
2 van Exel E, Gussekloo J, Houx P, et al. Atherosclerosis and cognitive impairment are linked in the elderly. The Leiden 85-plus Study. Atherosclerosis 2002; 165: 353-59.
3 Gueorguieva R, Krystal JH. Move over ANOVA: progress in analyzing repeated-measures data and its reflection in papers published in the Archives of General Psychiatry. Arch Gen Psychiatry 2004; 61: 310-17.
