This thesis explored social and psychosocial factors from different phases in the lifespan and their relation to the occurrence of dementia and Alzheimer s Disease (AD) in late-life. Early life circumstances, such as education, midlife factors such as occupation, and an active and socially integrated late-life were investigated in relation to dementia and AD risk. All five studies are based on the Kungsholmen Project, a longitudinal population-based study of aging and dementia. The initial population consisted of all registered inhabitants who were 75 years and older and living in the Kungsholmen Parish in 1987. The major findings from the five research papers included in this thesis are summarized below.
Study I. We found that frequent (daily-weekly) engagement in mental, social, or productive activities was inversely related to dementia incidence. Relative risks (RR) and 95% confidence intervals (CI) were 0.54 (95% CI: 0.34-0.87), 0.58 (95% CI: 0.37-0.91), and 0.58 (95% CI: 0.38-0.91), respectively. Similar results were found when these three factors were analyzed together in the same model.
Study II. Less-educated subjects had a RR of 3.4 (95% CI: 2.0-6.0), and subjects with lower socioeconomic status (SES) had a RR of 1.6 (95% CI: 1.0-2.5) of developing AD. Low SES at 20 years of age, even when high at 40 or 60 years, was associated with increased risk. When both education and SES were introduced into the same model, only education remained significantly associated with AD.
Study III. A mental, social, and physical component score was estimated for each leisure activity. RR of dementia for subjects with higher mental, physical, and social component score sums were 0.71 (95% CI: 0.49-1.03), 0.61 (95% CI: 0.42-0.87), and 0.68 (95% CI: 0.47-0.99), respectively. The most beneficial effect was present for subjects with high scores in all or in two of the components.
Study IV. We found that inactivity, depressive symptoms, but not social network, were independently associated with increased risk of dementia. However, to be inactive, have depressive symptoms, and simultaneously have a limited/poor social network compared to having none of these factors showed the strongest association to dementia (RR=5.4, 95% CI: 2.1-13.9).
Study V. Complex work with data and people was associated with reduced risk of dementia (RR = 0.85, 95% CI: 0.75-0.96, RR = 0.88, 95% CI: 0.80-0.97 respectively). When education was included in the model these associations were no longer significant. The association between education and AD/dementia, however, was modified by the highest levels of complexity which had a protective effect even among lower-educated subjects (RR = 0.52, 95% CI: 0.29-0.95).
Summary. The five studies in the thesis identified several sources of cognitive stimulation throughout the lifespan and indicated that education above elementary level, higher levels of work complexity, and a broad spectrum of activities in old age are all related to decreased risk of dementia. The cognitive reserve model can be applied throughout the life course, from childhood to adulthood and late-life, and cognitive ability is modifiable at all stages of life. Conversely, dementia risk is increased by inactivity, loneliness, and low mood; and social isolation intensified the effect of these factors.
© Anita Karp, 2005