Thirteen studies were included in the review (sample size ranged from 60 to 5,055). There were eight cohort studies and five case-control studies. All studies satisfied at least half of the criteria for methodological quality. Follow-up (where reported) appeared to be conducted for up to 10 years. Some studies adjusted for confounding.
Five studies showed positive associations between participation in cognitive leisure activities in early and middle adulthood and reduced risk of Alzheimer's' Disease and other dementias. In particular, significant positive associations were noted between novelty-seeking activity such as learning a new skill or taking up a new hobby (OR 0.248, 97.5% CI, 0.139 to 0.443; one study), daily intellectual activity, such as completing jigsaws or crosswords (OR 0.84, 95% CI 0.72 to 0.98; one study) and decreased odds of developing Alzheimer's disease. Women were more likely than men to reduce their risk of Alzheimer's Disease after participating in intellectual-cultural activities (OR 0.42, 95% CI 0.18 to 1.00; one study). The absence of reading, writing and entertainment were all associated with significantly increased risks of Alzheimer's' Disease (two studies). A sixth study showed that television watching as an individual activity was associated with a significantly increased risk of developing Alzheimer's' Disease (OR 1.32, 95% CI 1.08 to 1.62; one study).
Six out of seven studies revealed a positive association between participation in a variety of cognitive leisure activities in later adulthood in terms of reduced risk for Alzheimer's' Disease and other dementias. One study found a significant association between reading and reduced risk of dementia (OR 0.49, 95% CI 0.35 to 0.68). Another study found that participating in three activities (including reading and television watching) was significantly more effective (RR 0.41, 95% CI 0.18 to 0.90) than two in terms of lower risk for dementia.