Date Published: March 21, 2017
Publisher: Public Library of Science
Author(s): Linda Clare, Yu-Tzu Wu, Julia C. Teale, Catherine MacLeod, Fiona Matthews, Carol Brayne, Bob Woods, Bruce L. Miller
Abstract: BackgroundPotentially modifiable lifestyle factors may influence cognitive health in later life and offer potential to reduce the risk of cognitive decline and dementia. The concept of cognitive reserve has been proposed as a mechanism to explain individual differences in rates of cognitive decline, but its potential role as a mediating pathway has seldom been explored using data from large epidemiological studies. We explored the mediating effect of cognitive reserve on the cross-sectional association between lifestyle factors and cognitive function in later life using data from a population-based cohort of healthy older people.Methods and findingsWe analysed data from 2,315 cognitively healthy participants aged 65 y and over in the Cognitive Function and Ageing Study Wales (CFAS-Wales) cohort collected in 2011–2013. Linear regression modelling was used to investigate the overall associations between five lifestyle factors—cognitive and social activity, physical activity, diet, alcohol consumption, and smoking—and cognition, adjusting for demographic factors and chronic conditions. Mediation analysis tested for indirect effects of the lifestyle factors on cognition via cognitive reserve. After controlling for age, gender, and the presence of chronic conditions, cognitive and social activity, physical activity, healthy diet, and light-to-moderate alcohol consumption were positively associated with cognitive function, together accounting for 20% (95% CI 17%–23%) of variance in cognitive test scores. Cognitive reserve was an important mediator of this association, with indirect effects via cognitive reserve contributing 21% (95% CI 15%–27%) of the overall effect on cognition. The main limitations of the study derive from the cross-sectional nature of the data and the challenges of accurately measuring the latent construct of cognitive reserve.ConclusionsCross-sectional associations support the view that enhancing cognitive reserve may benefit cognition, and maintenance of cognitive health may be supported by a healthy and active lifestyle, in later life.
Partial Text: Cognitive health is a major factor in ensuring the quality of life of older people and preserving independence. Cognitive health is the development and preservation of the multidimensional cognitive structure that allows older people to maintain social connectedness, an ongoing sense of purpose, and the abilities to function independently, to permit functional recovery from illness or injury, and to cope with residual functional deficits . The key components of cognitive health are mental abilities and acquired skills, as well as the ability to apply these so as to engage in purposeful activity .
Descriptive information for sociodemographic factors, cognitive function, chronic conditions, and lifestyle factors is shown in Table 1. Among the 2,315 participants, the mean age was 74 y (SD: 6.3), and 51% were women. The mean CAMCOG score was 93.4 (SD: 5.4; median: 94; interquartile range (IQR): 7). The average score for cognitive reserve was 28.6 (SD: 6.8), with a range between 9.7 and 62.0.
This study investigated the potential mediating effect of cognitive reserve on the association between cognitive function and potentially modifiable lifestyle factors through cross-sectional analysis of data from a population-based cohort of older people in Wales. The hypothesis that cognitive reserve plays a mediating role was largely supported. Cognitive and social activity, physical activity, regular light-to-moderate alcohol consumption, and healthy diet were all positively associated with cognitive function and together accounted for 20% of the variance in cognitive test scores. Smoking, however, was not associated with cognitive function. The results of the mediation analysis showed that cognitive reserve, indexed by education and occupational complexity, was an important mediator of the association between the four lifestyle factors and cognition, with indirect effects via cognitive reserve contributing 21% of the overall effect.