The association between occupational complexity and the risk of dementia: Results from case-control and twin analyses

The purpose of this study was to investigate the association between occupational complexity and the risk of dementia in two sets of analyses—matched case-control (N = 315 cases, N = 814 controls) and co-twin control (N = 102 pairs). Participants were all members of the Swedish Twin Registry aged 65 years or older who were screened for cognitive impairment the years of 1998 and 2002. For a majority of participants, information about midlife occupation was collected prospectively in 1967 or 1973. In 326 participants, for whom prospective data were not available, occupational information was obtained retrospectively. Occupational complexity was measured along four separate dimensions: substantive complexity of work, and complexity of work with data, people, and things. Results indicated that participants who had held occupations that involved greater complexity of work with people were at approximately 50% lower risk of dementia than participants whose occupations were low for complexity with people, independent of age, gender, and education. This finding was consistent across matched case-control and co-twin control analyses. Results were similar for men and women. Substantive complexity of work and complexity of work with data were also found to be protective, but their effect on the risk of dementia was inconsistent across analyses and was not found in the co-twin control analyses, which control for genetic and other unmeasured early environmental influences shared by siblings. Complexity of work with things was associated with dementia only when category Housewives was included. Multivariate analyses indicated that complex work with people was protective when the effects of complexity of work with data and with things were taken into account. Overall, findings suggest that greater complexity of midlife occupation, particularly on the dimension of work with people, may reduce the risk of dementia. This finding holds even when age, gender, education and familial factors shared by twins are taken into account.