The dynamic relationship between cognitive function and positive well-being in older people: a prospective study using the English Longitudinal Study of Aging

Abstract

There is evidence that having a stronger sense of positive well-being may be a potential resource for healthier aging as represented by slower physical decline, reduced risk of frailty and longer survival. However, it is unclear whether positive well-being is protective of another crucial component of healthy aging, cognitive function, or whether it has a bidirectional relationship with cognitive function. We use multilevel models with within-person centering to estimate the within- and between-person association between cognitive function and positive well-being in 4 waves of data from the English Longitudinal Study of Ageing (ELSA), (N = 10985, aged 50-90 years at wave 1). Our findings show that, although most variation in cognitive function was explained by age, and most variation in well-being was explained by depression, small but significant associations between cognition and well-being remained after variation in age and depression were controlled. In models where cognition was the outcome, the association was mainly because of variation in mean levels of well-being between persons. In models where well-being was the outcome, the association was mainly because of within-person fluctuation in cognitive test performance. Exercise and depression were the most important moderating influences on the association between cognition and positive well-being. Depression had greater effect upon this association for those with higher well-being, but exercise protected cognitive performance against the adverse effects of lower well-being.

Figure 1

Model-predicted trajectories of age-related change in cognition and well-being. Note: The trajectories were predictions of the full models (reported in Tables 5 and 6) with all other covariates held constant at their respective means (equivalent to residualizing). The four panels show: A, General cognition; B, Executive function; C, Memory; D, Processing speed. Solid lines show trajectories of cognition with gray bands indicating how this was moderated by a difference of one standard deviation in person-mean well-being (the PM effects reported in Table 6). For example, the vertical distance at age 70 from the solid line to the upper band in panel A is 0.098 (see Table 6). Dashed lines show trajectories of well-being with gray bands indicating a difference of one standard deviation in within-person cognition (the WP effects reported in Table 5).

Figure 2

The effects of exercise and depression on the relationship between cognition and well-being. Note: The graph shows the cognition outcome for a range of person-mean well-being predicted using the fitted model of cognition reported in Table 6. The scales are in standard deviation units and person-mean well-being was mean-centered so 0 represents the average. The solid line represents the predicted outcome with all other independent variables held constant at their centered values. The dashed lines represent the effect for persons with 1 standard deviation greater exercise (upper dashed line) and depression (lower dashed line). The slope of each dashed line is the slope of the solid line (0.0982) plus the respective interaction effects (−0.0303 and −0.0242, see Table 6). The intercept differences between the solid and dashed lines are the respective main effects (0.0661 and −0.0497, see Table 6).