Secular trends in the prevalence of dementia and depression in Swedish septuagenarians 1976-2006

Background. It is not clear whether the prevalence of dementia and depression among the elderly has changed during the past 30 years. Method. Population-based samples from Gothenburg, Sweden were examined with identical psychiatric and neuropsychiatric examinations at age 70 years in 1976-1977 (n=404, response rate 78.8%) and 2000-2001 (n=579, response rate 66.4%), and at age 75 in 1976-1977 (n=303, response rate 78%) and 2005-2006 (n=753, response rate 63.4%). Depression was diagnosed according to DSM-IV and dementia according to Kay's criteria. General linear models (GLMs) were used to test for differences between groups. Results. Dementia was related to age but not to birth cohort or sex. Major depression was related to sex (higher in women) but not to birth cohort or age. Minor depression was related to birth cohort, sex (higher in women), age (higher at age 75) and the interaction effect of birth cohortxage; that is, the prevalence of minor depression increased with age in the 2000s but not in the 1970s. Thus, the prevalence of minor depression was higher in 2005-2006 than in 1976-1977 among 75-year-olds for both men (12.4% v. 3.7%) and women (19.1% v. 5.6%) whereas there were no birth cohort differences at age 70. Conclusions. Secular changes were observed only for minor depression, which is considered to be related more to psychosocial factors than major depression. The high prevalence of minor depression in later-born birth cohorts emphasizes the importance of detecting minor depression in the elderly.