Ageing and the epidemiology of multimorbidity

Abstract

The world's population is ageing and an important part of this demographic shift is the development of chronic illness. In short, a person who does not die of acute illnesses, such as infections, and survives with chronic illnesses is more likely to develop additional chronic illnesses. Chronic respiratory diseases are an important component of these diseases associated with ageing. This article reviews the relationship between ageing and chronic respiratory disease, and also how certain chronic diseases cluster with others, either on the basis of underlying risk factors, complication of the primary disease or other factors, such as an increased state of inflammation. While death is inevitable, disabling chronic illnesses are not. Better understanding of how individuals can age healthily without the development of multiple chronic illnesses should lead to an improved global quality of life.

Figure 1

Total world population growth from 1800–2050. Reproduced from [1].

Figure 2

Relationship of life expectancy at birth in years and fertility (children born per females) at three points of time worldwide. Each dot represents a country, with the size of that dot proportional to the country population. Free material from www.gapminder.org.

Figure 3

The ageing pyramid is a graphic representation of population composition changes between a, b) 1970, c, d) 2013 and e, f) 2050 projection, stratified by less (a, c, and e) and more developed regions (b, d and f), sex, and age strata. Reproduced from [4] with permission from the publisher.

Figure 4

a) Comparison of causes of death in 1990 and 2010 expressed as percentage of total deaths. Data from [7]. b) Leading causes of death worldwide for both sexes and all ages. UI: uncertainty interval. Data from [8]

Figure 5

Global distribution of disability-adjusted life-years (DALYs) ranking in three different age groups: a) 15–49 years, b) 50–69 years, and c) 70 years and older) at two time points (1990 and 2010). DALYs are calculated as years of life lost plus years lost due to disability (table 1). UI: uncertainty interval. Data from [8].

Figure 6

Chronic obstructive pulmonary disease prevalence by region. Data from [17, 18].

Figure 7

Global prevalence of chronic obstructive pulmonary disease (COPD) and risk factors. PM10: particulate matter <10 μm in diameter; TB: tuberculosis. Data from [17, 18].

Figure 8

Number of chronic comorbidities by age stratum. The number of comorbidities increases with age and is larger in individuals 65 years and older. Reproduced from [28] with permission from the publisher.

Figure 9

US Medicare claims disease network map. Nodes are diseases classified according to International Classification of Diseases (ICD)9 codes at the five-digit level. Link weight corresponds to the association between diseases. The blue area represents the respiratory disease neighbourhood and the grey area represents the interlinked comorbidities neighbourhood. Reproduced and modified from [41].