Population studies on depression in the elderly. Prevalence, incidence and relation to cognitive function and dementia

Abstract

Aims: To study the prevalence and incidence of depression in relation to cognitive function, dementia and brain atrophy in a representative sample of elderly persons. Methods: 70 and 74-year-old women (n=501) were studied in 1992-93 as part of the fourth phase of the Prospective Population Study of Women in Gothenburg, Sweden. These women had previously been examined in 1968-69, 1973-74 and 1980-81. Another representative sample (N=392, 166 men and 226 women) was studied at the age of 70, in 1970-71, as part of the Gerontological and Geriatric Population Studies in Gothenburg, Sweden (H70). These subjects were invited for follow-up examinations at 75, 79, 81, 83, 85 and 88 years of age. An extended sample was examined at the age of 85 (n=494), including 100 of the original sample. The investigation included a psychiatric examination, interview of a close informant, a neu-ropsychological examination and a CT scan of the head. The diagnoses were made according to the DSM-IIIR criteria. Dementia syndrome was diagnosed according to the ICD-9 in the longitudinal examinations. Case records were examined regarding information on lifetime depression and dementia. Results:Paper I. The prevalence of depression in 70 and 74-year-old women was 11.6 %, including 8.4% with major depression (MDD). Among those who were currently mentally healthy, 43.0 % had a history of previous depression. Women with current major depression had lower scores on the MMSE than the mentally healthy women. This association was only found in women with the lower level of education. Current depressives, previous depressives and mentally healthy women without a history of depression did not differ regarding brain atrophy or white matter lesions on CT. The association between MDD and lower cognitive performance was independent of structural brain changes on CT.Paper II. The incidence of depression was 12/ per 1000 person-years in men and 30/ per 1000 person-years in women between the ages of 70 and 85 (p=0.001). The incidence increased from 17/ per 1000 person-years (men 8.7, women 23.2, p=0.007) between the ages of 70 and 79 to 44/ per 1000 person- years (men 27.0, women 52.8, p=0.166) between 79 and 85 (age difference RR 2.6; p< 0.001, men RR 3.1; p=0.036, women RR 2.3; p=0.003). A diagnosis of depression was associated with increased mortality and refusal rate during the 15-year follow-up. Previous episodes of depression were associated with an increased risk of new episodes. The prevalence of depression increased from 5.6% at the age of 70 to 13.0% at the age of 85. The lifetime prevalence of depression was 23% in men and 45% in women. Paper III. Among 85-year-olds with low education, the depressed performed worse than the mentally healthy in the Mini Mental State Examination, whereas this distinction was not evident among individuals with higher education. Measures of brain atrophy were similar in depressed and mentally healthy 85-year-olds. Early-onset major depression but not late-onset depression was associated with an increased three-year incidence of dementia.Paper IV. Individuals with major depression performed worse than those mentally healthy in tests of verbal ability, inductive logical reasoning, spatial ability, perceptual speed and secondary memory. There were no differences between the groups regarding basic arithmetics and primary memory. There were no differences between early and late-onset depressives. Individuals with low motivation during the neuropsychiatric examination were more cognitively impaired in the psychological tests. Decreased concentration and psychomotor retardation were the individual symptoms of MDS that typically contributed to lower test scores. Paper V. History of depression did not increase the risk of dementia in men and women compared to those never depressed during the 18-year follow-up period.