The ageing population
An epidemiologic approach to a fundamental public health issue
The demographic structure and dynamic have been in focus among Swedish scientists and politicians on several occasions during the previous century. It is currently a prioritised issue because of the rapid increase in the number and percentage of old and very old people. This will have a big impact on society through increased demands on the health care system and through consequences for social security systems, including retirement age. A drastic reduction in the number of births in combination with a continuous reduction in mortality has led to the present population structure.
Mortality can be followed in Sweden for over 250 years. Over that period, life expectancy has increased from 40 to 80 years, an average of 2 months per year. This trend continues to date. Reduction in childhood mortality explains most of this change during the early period, but there have been reductions over the entire age span. Currently, mortality reduction among the old and very old attracts considerable interest. Two questions are at the forefront of interest among scientists.
First, is it reasonable to assume that the mortality reduction will continue or is it approaching an end; linked to this is the question of what causes the mortality reduction. A commonly held view is that the survival curve is becoming increasingly rectangular since more and more people survive to an age closer to maximum life span. If this were true, the life expectancy increase would gradually slow down as it approaches the maximum life span (1). However, this hypothesis is not supported by data which show that life expectancy (in the record keeping countries) continues to increase almost linearly with no indications of levelling off (2). An additional interesting piece of information comes from Swedish data. To test the hypothesis of a maximum life span, the age of the oldest person to die was analysed over time (3). It turned out that this oldest age of dying actually increased over time. This suggests that even if a maximum life span exists we are not quite there yet. Thus, the quest to find out how long the mortality reduction goes on.
Directly linked to this are questions about determinants of longevity. These questions are addressed from several different angles including molecular genetics using telomere length as a biomarker of ageing and of course by close scrutiny of mortality patterns (4). Doll and Peto discussed this in a BMJ paper in 1997 postulating that there is no such thing as ageing, but only a lifelong accumulation of risk factors (5).
The research area of longevity, its determinants and consequences is of major societal importance and at the heart of public health sciences. It is an area that links public health, epidemiology and demography. Sweden has unique data for research along these lines because of very long historical records and excellent current mortality data along with other relevant information.
Aims of project
The overall aim of this project is to investigate to what extent is the reduction in old age mortality due to a delayed onset of diseases, to a higher survival rate or a longer survival time among those with disease?
Another aim is to investigate how healthy the very old people will be in the future? The core of this question is whether it is reasonable to assume that age specific health will remain unchanged over time, despite the decrease in age specific mortality rates, or whether it is more likely to assume that age-specific disease rates (CHD and stroke) will decrease in parallel with decreasing mortality rates? This question is of utmost importance for society because it affects health care demands and retirement age
The studies will be based on Swedish national register data. It contains practically all individuals resident in Sweden, depending on birth year, and a linkage is made of several national registers such as the Register of the Total Population, the Population and Housing Census, the Cause of Death Register and the Hospital Discharge Register in order to obtain information about mortality and morbidity on an individual level.
The project has started up during 2010 and will continue for at least two years.