Demographic projections suggest that the populations of all countries are ageing, which will have wide-ranging effects on social, economical, and health systems. The world's population aged 60 years and older is set to rise from 841 million in 2013, to more than 2 billion by 2050, and exceed the number of children by 2047. By 2050, 21·1% of the world population will be 60 years or older, and 80% of this demographic group will live in low-income and middle-income countries, compared with about two-thirds at present. During the same period, global life expectancies are predicted to rise, reaching 83 years in high-income regions and 75 years in low-income and middle-income regions by 2045–50; when compared with life expectancy figures for 2010–15, the gap between life expectancies in more developed and less developed world regions is expected to narrow.1 The population aged 60 years and older in less-developed regions is projected to rise from 554 million in 2013 to nearly 1·6 billion by 2050, because the annual growth rate of this section of the population in these regions is almost three times that in more-developed regions of the world. This growth in the older population is taking place in parallel with increasing inequalities in income, disparities in access to health care and social-support systems, and widening health gaps as a result of complex patterns of disease burden and globalisation of health risks. In most developing countries, these issues are compounded by a lifetime of accumulated health risks associated with poverty and inadequate access to health care. The changing epidemiological profiles in low-income and middle-income countries are largely driven by a set of conditions, such as rapid urbanisation, and changing dietary habits and levels of physical activity, that are different from those that were prevailing when these shifts in profiles happened in the high-income countries. Older populations are showing an increase in the incidence and prevalence of chronic non-communicable diseases that occur before the onset of old age with a natural history that takes place in conditions of poverty—these have been referred to as post-transitional illnesses in pretransitional circumstances.
In view of these trends, there has been much speculation about the health that this ageing cohort will have, such as: will the years gained be productive and healthy, or will elderly people live longer lives in conditions of ill health? Three main hypotheses have been proposed to address this question.2 The compression of morbidity hypothesis posits a situation for which the age of onset of morbidity is delayed to a greater extent than life expectancy rises, thereby compressing morbidity into a short period at a late age.3 The expansion of morbidity hypothesis maintains the opposite, that increases in life expectancy are matched or exceeded by added periods of morbidity.4 Both compression and expansion of morbidity could happen in absolute or relative terms—ie, changes in the absolute number of years lived with disability—or in terms of healthy life expectancy as a proportion of total life expectancy.
Key messages
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Populations are rapidly ageing worldwide with major implications for health systems. This situation is more prevalent in low-income and middle-income countries
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A key question is whether older generations will be healthier than those who have preceded them. In other words, will we be adding life to years as populations age by ensuring maintained functioning and wellbeing?
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High-income countries show some evidence that a compression of morbidity (a reduction over time in the total lifetime days of disability) is taking place, as noted from trends of functioning and disability status. However, uncertainty remains about the health of future older generations in view of the different risk factor exposures in different cohorts and increases in the prevalence of chronic diseases
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Low-income and middle-income countries currently have no reliable evidence of compression, and morbidity might even be expanding, driven by lifestyle risk factors and increasing prevalence of chronic diseases
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In view of the shortage of data, robust evidence needs to be generated about these trends to ensure an appropriate response from health and social systems
Healthy life expectancy is a measure that combines mortality and morbidity information in one index, expressing the number of healthy years of life lost because of poor health, and incorporating a range of severities to quantify poor health, which are based on different weights being assigned to different severity levels of disability that have resulted from various disorders. Data from the Global Burden of Disease 2010 study5 show that from 1990 to 2010, as life expectancy rose healthy life expectancy increased more slowly, and little progress was made in the reduction of the non-fatal health effects of diseases. For example, during this period, men aged 50 years had a healthy life expectancy increase of 0·75 years for each year of increase in life expectancy. The corresponding rise in healthy life expectancy for women aged 50 years was 0·77 years. Although total life expectancy in Japanese women—currently the highest in the world with also some of the lowest disability levels in the world—increased by 3·9 years, healthy life expectancy increased only by 3·2 years during the same period.5
Evidence for the theory of equilibrium of morbidity lends support to a more multidimensional perspective, for which lessened progression and severity of morbidity are accompanied by rises in moderate or mild morbidity.6 Data suggest that although severe disability-free life expectancies might have decreased in some high-income countries during the past four decades, total disability-free life expectancy has stagnated.7 In fact, in older adults, morbidity might have expanded.8 Health interventions that are targeted at lethal diseases could lead to increased years spent with a disability, which suggests that dissemination and uptake of lifestyle change interventions that reduce risk across a range of chronic disorders are essential. The coexistence of many diseases in an individual could mean that when mortality due to one disorder is prevented, disability due to another might become increasingly important.
Although life expectancy is clearly rising, the patterns of increase have not been consistent, with variable surges and periods of stagnation.9 Whether gains in life expectancy will occur at a diminishing rate, or continue indefinitely, is under debate.6 Investigators of studies of morbidity trends have drawn conflicting conclusions, and the quality of studies themselves are subject to several design and contextual factors, including the definition of morbidity, period studied, and study population.9, 10 Several review studies from high-income country settings have reported a fall in disability during the past few decades,3, 11, 12 with concurrent increases in prevalence of chronic diseases;13, 14, 15, 16 however, these studies did not contain evidence from people aged 85 years and older.9
By contrast, in 2007, a review by the international Organisation for Economic Cooperation and Development (OECD) that used disparate data reported by countries, showed that although there is clear evidence of a reduction in disability in elderly people in five of the 12 countries studied, in other countries rates are increasing or stable. Although prevalence of most of these disorders and risk factors has increased, no clear judgment could be made about the link between chronic disorders and severe disabilities. The OECD investigation relied on a proxy operationalisation of severe disability— namely, one that was most clearly consistent with the available national, self-report, survey data, and was intuitively linked to long-term care needs. The study investigators concluded that “it would not seem prudent for policy makers to count on future reductions in the prevalence of severe disability in elderly people, but rather to expand national capacity in long-term care and programmes to prevent or postpone chronic conditions”.
The situation in low-income and middle-income countries is much less studied, with very few data available. Delineation of the path of health and morbidity in old age has important implications for public health and the economy in terms of aspects of medical spending,17 planning of social programmes,18 prediction of trends in the workforce,18 and the social patterning of poverty.19
We identified data for this Series paper, by searches of PubMed (Medline) and CABI Global Health Database on June 17, 2011. We used four classifications of search words, relating to older age; morbidity, activities of daily living, disability, impairment, length of hospital stay, chronic disease, and health status; life expectancy, and actuarial analysis; and trends. Only articles published in English between 1991 to present were included. Specifically, we aimed to answer these questions: have there been changes in the age of onset or severity of late-life morbidity, in relation to life expectancy? Which hypotheses of health and ageing trends have been supported by published work?
Second, we also undertook new analyses of publicly available crossnational datasets that contain harmonised items related to the health status of older adults during many periods. In these analyses we addressed several related questions—has the proportion of older adults with a disability remained stable, increased, or reduced over time? Is this change due to the effects of age or is it a cohort effect? What are the factors that affect these longitudinal trends? And how do these patterns compare across countries? We used data from all the years that are available for public use.
We focused our analysis on trends in functioning in older adults because the review by Prince and colleagues in this Series20 addresses the issue of trends in chronic diseases in far greater detail. An analysis of data from the Global Burden of Disease study5 shows that nearly a quarter of all disease burden globally is carried by those aged 60 years and older, and that the per person burden is higher in developing countries, driven mainly by cardiovascular and respiratory diseases, and sensory impairments.