ABSTRACT
In a similar vein, identification of "preclinical dementia" is no easy task, and even after 7 years, possible prodromal effects may still be operating. There is the possibility, for example, that depression may be either a prodrome for dementia, or a reaction to early cognitive impairment. Depression is, of course, linked to reduced activity levels, and may also be an important factor to take into account. Evidence regarding the effects of depressive symptoms on cognitive decline and the development of Alzheimer's disease is emerging from both the Religious Orders cohort and the Chicago biracial cohort. Wilson et al. (2002c) report that in the Religious Orders cohort, the greater the number of depressive symptoms at baseline, the greater the risk of developing Alzheimer's disease (with the risk increasing by 19% per depressive symptom). Depressive symptoms were also related to greater change on an index of global cognitive function. This finding was replicated in the Chicago cohort (Wilson, Mendes de Leon, Bennett, Bienias, & Evans, 2004) with number of depressive symptoms at baseline predicting cognitive decline in a group of 4392 older people followed up for an average period of 5.3 years, and controlling for education and initial level of cognition. Wilson et al. conclude that their findings do not reflect a depressive reaction to cognitive impairment but that "chronic experience of even relatively low levels of depressive symptoms may compromise the hippocampus and perhaps other neural systems...."
