A very long-running study, in which 800 Swedish women (aged 38-54) were followed for 44 years, found that women with a high level of mental activities in midlife were 46% less likely to develop Alzheimer's disease and 34% less likely to develop dementia overall, compared with women with the low level of mental activities. Women who were physically active were 52% less likely to develop dementia with cerebrovascular disease and 56% less likely to develop mixed dementia, compared with women who were inactive.
Mental activities included intellectual activities, such as reading and writing; artistic activities, such as going to a concert or singing in a choir; manual activities, such as needlework or gardening; club activities; and religious activity.
Participants were given scores in each of the five areas based on how often they participated in mental activities, with a score of zero for no or low activity, one for moderate activity and two for high activity. For example, moderate artistic activity was defined as attending a concert, play or art exhibit during the last six months, while high artistic activity was defined as more frequent visits, playing an instrument, singing in a choir or painting. Low activity was defined as scores of zero to two and high activity as scores of three to 10 (44% and 56% of participants, respectively).
The physically active group ranged from light physical activity such as walking, gardening, bowling or biking for a minimum of four hours per week to regular intense exercise such as running or swimming several times a week or engaging in competitive sports. Most (82%) were in the active group.
Of the 438 women with the high level of mental activity, 104 (23.7%) developed dementia, compared to 90 (25.9%) of the 347 women with the low level of activity. Of the 648 women with the high level of physical activity, 159 (24.5%) developed dementia, compared to 35 (25.5%) of the 137 women who were inactive.
I note that distinction between those with high and low levels of activity seems very broad-brush. I don’t know why the researchers didn’t analyze the data in a more refined manner — comparing the most active with the least active would be more usual, and would be more likely to show a greater effect. But perhaps that's the point — showing that even with this smaller distinction, a significant effect is still found.
During the study, 194 women developed dementia. Of those, 102 had Alzheimer's disease, 27 had vascular dementia, 41 had mixed dementia, and 14 had other dementias. 81 (41.8%) of those with dementia also had cerebrovascular disease.
Full text available at https://n.neurology.org/content/early/2019/02/21/WNL.0000000000007021
(2019). Cognitive and physical activity and dementia.
Neurology. 92(12), e1322.