Cognitive Impairment in the Non-demented Elderly. Occurrence, Risk Factors, Progression



This doctoral thesis investigated different issues related to cognitive impairment (CI)  in the nondemented elderly, including occurrence of CI, risk factors leading to CI  development, and progression of CI to dementia. Data were derived from the  Kungsholmen Project, a community-based study of 75+ years old (Studies II and IV),  and from the HARMONY Study (Studies I and III), a nation-wide, population-based  study of twins in Sweden. The major findings are summarized below. Study I. The prevalence of subjective cognitive impairment (SCI) and cognitive  impairment no dementia (CIND) was estimated among nondemented elderly twins.  Prevalence rates of SCI and CIND were 39 (38 to 39) and 25 (24 to 25) per cent. SCI  was more prevalent among married people with higher education and occupational  SES. A reverse pattern was observed in CIND. Both SCI and CIND were more  prevalent among older compared to younger old. Probandwise concordance and  tetrachoric correlations for SCI and CIND did not differ between monozygotic and  dizygotic same-sex twins. Study II. The incidence of amnestic mild cognitive impairment (aMCI), other  cognitive impairment no dementia (oCIND), and dementia was estimated using 9-year follow-up data. Incidence rates per 1,000 person-years of aMCI, oCIND and  dementia were 11.4 (8.6 to 15.1), 33.8 (28.7 to 39.8), and 70.4 (64.0 to 77.4). Both  aMCI and oCIND incidence increased with advancing age in a nonlinear fashion.  When correcting for attrition due to death, the increase with age appeared more linear  and was similar to that observed for dementia. Study III. The association of common chronic diseases with SCI and CIND was  investigated, taking into  account familial factors.  In fully adjusted models, mental,  musculoskeletal, respiratory, and urological diseases were associated with increased  odds of both SCI and CIND. Gastrointestinal disorders were related to SCI, while  endocrine diseases were associated with CIND. Multimorbidity was associated with 100% and 50% increased odds of SCI and CIND, respectively. In co-twin control  analyses, the chronic diseases-SCI association remained significant, but the  association with CIND was largely attenuated. Study IV. Low mood was investigated in relation to aMCI and oCIND and their  progression to dementia. People with low mood at baseline had a 2.7-fold (95% CI  1.9 to 3.7) increased risk of developing MCI at follow-up. The association was  stronger for aMCI (HR 5.8; 95% CI 3.1 to 10.9) compared with oCIND (HR 2.2; 95%  CI 1.5 to 3.3). Low mood at baseline was associated with a 5.3-fold (95% CI 1.2 to  23.3) increased risk of progression to dementia in aMCI. Conclusions. Cognitive impairment is highly frequent in the elderly population.  Rates increase with age, especially when detected longitudinally and corrected for  attrition. Other sociodemographic factors can also affect the distribution of CI among  the nondemented. Co-morbid chronic diseases and multimorbidity are associated to  increased odds of subjective and objective CI, while low mood is a strong predictor of  CI development and progression in the cognitively healthy elderly. Familial factors  contribute to non-dementia CI in a complex fashion.

© Barbara Caracciolo, 2011.