Prevalence and impact of chronic diseases and multimorbidity in the aging population : a clinical and epidemiological approach

Abstract

Due to the aging of the population, the absolute number of subjects affected by age-related diseases is expected to increase as well as their coexistence known as multimorbidity.The aims of this thesis were to evaluate the prevalence, distribution and patterns of chronic multimorbidity in the elderly population, and its impact on disability, functional decline and mortality. The data were gathered from the Kungsholmen Project (Study I, II, and III) and from an Italian database on the hospitalized elderly (Study IV). The Kungsholmen Project is a longitudinal population-based study on 75+ year-old people, living in Stockholm, Sweden, who were clinically re-examined every three years. The Italian database includes clinical data from 923 patients, 65+ year-old, admitted to an acute geriatric ward in the Spedali Civili Hospital, Brescia, Italy.

Study I. Cardiovascular and mental diseases emerged as the most common chronic disorders in both men and women. However, cardiovascular diseases reached a plateau after 75 years (55%), whereas mental disorders continued to rise with increasing age from 18% in the 77-84 year-old to 36% in 85+ year-old subjects. The prevalence of multimorbidity was 55%. Older age, female gender, and lower education were independently associated with a more than 50% higher occurrence of multimorbidity.

Study II. Heart failure and visual impairments were the diseases with the highest comorbidity (mean: 2.9 and 2.6 co-occurring conditions, respectively) while dementia had the lowest (mean: 1.4 comorbidities). Further, heart failure very rarely occurred without any comorbidity (0.4%). The observed prevalence of comorbid pairs of conditions exceeded the expected one for many circulatory diseases, and also for dementia and depression, which were further correlated to hip fracture and cerebrovascular diseases. The cluster analysis showed five clusters, three of which grouped circulatory, cardiopulmonary, and mental diseases. The last two clusters included only one disease (diabetes and malignancy) together with their consequences.

Study III. During a 3-year follow-up, of 1099 old persons, 363 died and 85 showed functional decline. The number of chronic conditions incrementally increased the risk of functional decline. The Relative Risk (RR) increased from 1.5 in subjects with one disease to 8.0 in persons with 5+ diseases. However, this was not the case for mortality. Baseline disability had the highest impact on survival, independently of the number of diseases (RR= 7.8; 95% Confidence Interval (CI) = 4.6-13.4 in subjects with one disease; RR= 6.9;95% CI=4.2-11.3 in those with 2+ diseases) and amplified the effect of multimorbidity on further functional decline (RR= 11.6;95% CI= 4.1-32.9 for persons with both multimorbidity and disability).

Study IV. In a cohort of geriatric patients, older age, poor cognitive status, and depression were associated with functional disability at hospital discharge in all age groups, whereas multimorbidity was independently correlated with disability only in the older patients (75+ yrs) (OR=1.5;95%CI=1.2-2.0), in particular among those who were cognitively impaired (OR=4.0;95%CI=2.0-8.1). Cognitive impairment and depression showed an additive effect on disability especially in the younger patients (65-74 yrs).

In conclusion, multimorbidity is the most common clinical situation in the aging population, affecting mostly the very-old and women. Poor education is associated with an increased risk of multimorbidity, suggesting that risk behaviors learnt in early life may still affect the health status of old persons. Disability and functional decline increase with increasing number of chronic conditions. Moreover, the impact of multimorbidity on disability differs depending on age and could be severer in the cognitively impaired elderly. Finally, disability seems to have greater impact on survival than multimorbidity. Assessing multimorbidity, disability and depression leads to the identification of groups of old persons particularly at risk of functional decline who should be a target for clinical and preventative intervention.