THE EFFECTS OF INTELLIGENCE AND EDUCATION ON THE DEVELOPMENT OF DEMENTIA - A TEST OF THE BRAIN RESERVE HYPOTHESIS

Background. A number of recent epidemiological studies have shown that the prevalence and incidence of dementia are increased in population strata with low compared to high levels of education. this has been ex plained as a consequence of a greater 'brain reserve capacity' in peop le with a high level of education. theoretically, however, brain reser ve capacity is better reflected by intelligence than by level of educa tion. Thus, the emergence of dementia will be better predicted by low pre-morbid intelligence than by low education. Methods. This predictio n was tested in a population based sample of elderly subjects (N = 206 3; age range 65-84; Amsterdam Study of the Elderly) who were followed over 4 years. Dementia was diagnosed using the Geriatric Mental State examination (GMS). Pre-morbid intelligence was measured using the Dutc h Adult Reading Test (DART), a short reading test which gives a good e stimate of verbal intelligence, and is relatively insensitive to brain dysfunction. The effects of age, gender, occupational level, number o f diseases affecting the central nervous system and family history of dementia or extreme forgetfulness were also examined. Results. Logisti c regression analysis showed that low DART-IQ predicted incident demen tia better than low level of education. A high occupational level (hav ing been in charge of subordinates) had a protective effect. Conclusio ns. This result supports the brain reserve theory. It also indicates t hat low pre-morbid intelligence is an important risk factor for cognit ive decline and dementia. Use of reading ability tests is to be prefer red over years of education as estimator of pre-morbid cognitive level in (epidemiological) dementia research.