Occupation type as a predictor of cognitive decline and dementia in old age

OBJECTIVE: To assess whether an individual's main occupation predicts cognitive decline or dementia. METHODS: The data were taken from a longitudinal study of 518 men aged 70 or over. Main occupation was coded into one of John Holland's six occupational categories. The subjects completed four cognitive tests and were diagnosed for dementia on two occasions three and a half years apart. The cognitive tests were the Mini-Mental State Examination, Episodic Memory Test, Symbol-Letter Modalities Test and National Adult Reading Test. Informants also completed the Informant Questionnaire on Cognitive Decline in the Elderly. Dementia was diagnosed by the American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders, 3rd edition, revised (DSM-III-R) and ICD-10 criteria using the Canberra Interview for the Elderly. RESULTS: Cross-sectional analysis of the wave 1 data showed that the realistic occupations, which include trade, technical and some service occupations, had poorer cognitive performance and a higher prevalence of DSM-III-R dementia. These differences held even when age, education and native English were statistically controlled. The greatest occupational difference was on the National Adult Reading Test, which estimates pre-morbid ability. By contrast, there were no occupational differences in longitudinal change in cognitive test performance, informant reports of cognitive decline or incident cases of dementia over three and a half years. CONCLUSION: Cross-sectional occupational differences on cognitive tests and in dementia prevalence are due to differences in pre-morbid ability rather than to differences in rate of cognitive decline.