Department of Public Health, Erasmus University Rotterdam, The Netherlands.
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Abstract |
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Methods We used data on the population and the number of deaths by age, sex and underlying cause of death for 19701994. Life expectancy at age 60 and 85 was estimated using standard life-table techniques. The contribution of different ages and causes of death to the change in life expectancy during the 1970s (1970/74 1980/84) and the 1980s (1980/841990/94) were estimated with a decomposition technique developed by Arriaga.
Results Life expectancy at age 60 increased in the 1970s and 1980s, whereas life expectancy at age 85 decreased (men) and stagnated (women) in the 1980s, and has decreased in both sexes since 1985/89. The decomposition by age showed that constant mortality rates in women aged 8589, and increasing mortality rates at ages 85+ (men) and 90+ (women) have caused this lack of increase in life expectancy. The decomposition by cause of death showed that smaller mortality reductions from other cardiovascular and cerebrovascular diseases, which contributed most to the increase in life expectancy at age 85 in the 1970s, and mortality increases from, amongst others, chronic obstructive pulmonary disease (COPD), mental disorders and diabetes mellitus produced the decrease (men) and plateau (women) in life expectancy at age 85.
Conclusions Life expectancy at advanced ages stopped increasing during the 1980s in The Netherlands due to mortality increases at ages 85+ (men) and 90+ (women). Cause-specific trends suggest that, in addition to (past) smoking behaviour in men, changes in the distribution of morbidity and frailty in the population might have contributed to this stagnation.
Keywords Old-age mortality, life expectancy, cause-of-death, decomposition by age, decomposition by cause of death
Accepted 17 August 1999
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Introduction |
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This impressive increase in length of life has been accompanied by substantial changes in the age-at-death and cause-of-death patterns. Changes in the cause-of-death pattern from mainly infectious diseases to chronic diseases were accompanied by a shift in the age pattern of mortality from younger ages to older ages.5 Since the early 1970s, declines in mortality from chronic diseases at older ages have caused sharp rises in life expectancy of the elderly population.57 Uncertainty abounds as to whether the decline in mortality at older ages will continue to generate substantial increases in life expectancy.
Two opinions are prevalent. One group of researchers, known as the proponents of the limited-lifespan paradigm, believes that average life expectancy will not increase beyond 85 years of age.810 Further substantial reductions in death rates at advanced ages are constrained by biological barriers (e.g. senescence) and/or by societal barriers (e.g. environmental deterioration). The increasingly rectangular shape of the survival curve, seen as a manifestation of the fact that the natural limit to human life has almost been completed,9 and the enormous reductions in mortality rates which would be needed to achieve a life expectancy at birth of 85 years10 are used as arguments in support of this view.
Others, known as proponents of the mortality-reduction paradigm,1115 argue that the decline in mortality rates will continue and may even accelerate, including also the most advanced ages. A life expectancy at birth of 100 years or more is considered to be within reach somewhere in the near future.12,13 The observed decrease in mortality at advanced ages of 12% per year, and the very low mortality rates in subpopulations with healthy life styles, are used as arguments in favour of substantial future increases in life expectancy.11,13
Several studies have reported rapid declines in oldest-old mortality.7,11,1618 In the Netherlands, too, a country with traditionally low mortality and reliable mortality data at advanced ages,19 life expectancy of the elderly (65+) and the oldest old (85+) has increased.20 This study aims at obtaining a better understanding at the recent changes in mortality in the Dutch elderly population. The central questions are: (1) did the increase in life expectancy of the elderly population accelerate, continue or stagnate in past years and (2) which age- and cause-specific mortality dynamics underlay these recent changes in the life expectancy? We will use total and cause-specific Dutch mortality data of the population aged 60 in 1970/741990/94.
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Methods |
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Methods
We started with a description of the change in life expectancy at age 60 and age 85 in The Netherlands in 1970/741990/94. Life expectancies were estimated from complete life tables with age 105 as oldest age group. These life tables, each covering five calendar years, were constructed for both sexes from total mortality and population data, using standard demographic techniques.23,24
Next, we looked for explanations of the change in life expectancy at age 60 and 85 in the 1970s (1970/741980/84) and the 1980s (1980/841990/94) by examining the contribution of different age groups and causes of death to the change in life expectancy. This contribution was estimated from ageand cause-specific mortality data using a method developed by Arriaga,25,26 which decomposes the change in life expectancy into the contribution to this change of different age groups and/ or causes of death. Although changes in age and cause-specific mortality rates also give an indication of the contribution of different ages and causes to the change in life expectancy, we prefer the Arriaga method for two reasons. First, this method takes into account substitution between competing causes of death. Second, it takes into account the fact that similar changes in mortality rates at different ages influence life expectancybeing a population health measureto a different extent. The magnitude of the effect of (changes in) age- and cause-specific mortality rates on life expectancy is weighted (1) by the size of the life-table population in a certain age group exposed to the (changed) rate, and (2) the remaining life expectancy of that age group. Due to this implicit weighting in the life table, changes in mortality rates that are not important for the health of the population, for instance because the population at risk being exposed to these rates is rather small, are not weighted heavily. In general, changes at young ages have a larger impact on life expectancy than changes at advanced ages.27,28 This is due to the fact that (1) only a small proportion of the population is exposed to changes in mortality rates at advanced ages, as not everyone survives up to these ages and (2) the remaining life expectancy at older ages is much smaller, reflecting the high risks of mortality at older ages. It merits attention that life expectancy (and thus changes in life expectancy) is unaffected by the age distribution of the actual population, which enables comparisons to be made over time and between groups (e.g. by sex). The age distribution of the life-table population is only determined by the mortality rates.
Notwithstanding the favourable properties of life table based methods like the Arriaga method, examining changes in age- and cause-specific mortality rates is useful as well. Having assessed which age groups and causes of death contributed most to the change in life expectancy, looking at changes in age- and cause-specific rates will provide more insight into the exact changes. Therefore we also calculated directly standardized death rates (using the population of 1990/94 by 5-year of age up to age 95+ as standard) for each 5-year period. We expressed changes in standardized mortality rates as ratios of comparative mortality figures (CMF). To assess whether these changes in the ratios of CMF were statistically significant, we calculated 95% CI of the CMF ratios.29 In the presentation of the outcomes of the age-specific changes in total mortality, we focus on the change in CMF by 10-year age groups since 1970/74. Results for specific cause-of-death groups are not shown separately in Tables or Figures. Only cause-specific changes in mortality are presented separately for the age group 85+ in the 1980s, because changes in mortality in the oldest old have been striking since 1980/84 in The Netherlands30 and deserve a closer inspection.
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Results |
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Table 2 shows the contribution of different age groups to the change in life expectancy at ages 60 and 85 calculated with the Arriaga method. A positive contribution indicates that a mortality reduction in the relevant age group contributes to an increase in life expectancy, whereas a negative contribution indicates that a mortality increase contributes to a reduction of life expectancy. In the 1970s mortality reductions in all age groups contributed to the increase in life expectancy at age 60 and age 85, although the size of these contributions differed. The most striking development in the 1980s was that mortality changes at age
85 (men) and at age
90 (women) contributed negatively to the increase in life expectancy at age 60. At age 85, the same changes in mortality were responsible for the stagnating increase in life expectancy among women (0.02 years) and for the decline in life expectancy among men (0.22 years). That life expectancy at age 60 continued to increase was due to mortality reductions in the age groups between 60 and 84 years of age, which have a larger impact on life expectancy at age 60. For men, larger mortality declines at ages 6579 produced an even larger increase in life expectancy at age 60 in the 1980s, despite the unfavourable developments at older ages. For women the increase in life expectancy at age 60 was smaller than in the 1970s because the positive impact of mortality reductions below age 90 also shrank.
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Changes in age- and cause-specific mortality
Figure 1 shows the ratios of the standardized mortality rates (CMF) by 10-year age groups since 1970/74, using 1970/74 as reference (i.e. 1970/74 = 1). The developments in the 1970s and 1980s in mortality for each age group are clear at a glance. Whereas in the 1970s, mortality rates in all age groups decreased, in the 1980s only mortality rates in the age groups 6069 and 7079 continued to decline. In the age groups 8089 mortality rates stagnated (women) or increased slightly, but not significantly (men). Above 90+ a significant increase was observed in both men and women in the 1980s. As could be expected, the age groups which showed a mortality increase or a decline, are the same as those picked out by means of the Arriaga method. However, comparison of Figure 1 and Table 2 makes it clear that caution should be exercised when looking at changes in mortality rates in order to explain changes in life expectancy. For example, Figure 1 shows that the reduction in the CMF for age group 90+ was largest for men in the 1970s, whereas Table 2
shows that this age group did not contribute most to the increase in life expectancy at age 60. After all, the contribution of age group 7079 (0.1) was higher than that of 90+ (0.03).
Table 4 focuses on recent changes in mortality rates above age 85 from specific causes. For the ease of interpretation, we expressed the change as the ratio of the CMF in 1990/94 to that in 1980/84 (i.e. 1980/84 = 1). A ratio larger than 1 indicates an increase in mortality as compared to 1980/84, whereas a ratio smaller than 1 indicates a decline. Some causes of death showed mortality declines in the 1980s, but overall the situation was one of mortality increase. Significant increases in mortality above age 85 from mental disorders, diabetes mellitus and other endocrine, nutritional and metabolic diseases, COPD, diseases of the nervous system, diseases of blood and blood-forming organs, ill-defined conditions, prostate and other cancers, infectious/ parasitic diseases and pneumonia/influenza took place. These causes also contributed in a negative sense to the decline (men) and plateau (women) in life expectancy at age 85 (Tables 3a, 3b
).
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Discussion |
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Before turning to the meaning and implications of our results, it must be emphasized that the findings, which are based on underlying cause-of-death data, might be subject to coding and classification errors. First, at advanced ages, underlying causes of death are difficult to assess and may therefore be unreliable.31 Furthermore, estimates of the magnitude of the effects of IHD and other heart diseases might be biased, due to the ICD Revision of 1979. The number of deaths from these causes by calendar year showed a small increase for other heart diseases mirrored by a decrease for IHD between 1978 and 1979. Finally, the effect of diabetes mellitus and mental disorders might be overestimated due to a more frequent classification of diabetes mellitus32 and senile dementia (part of mental disorders; personal communication Statistics Netherlands) as underlying cause of death in The Netherlands since 1983 and 1992, respectively. The number of deaths from diabetes by calendar year showed an increase in diabetes deaths in the years immediately after 1982. For senile dementia the increase started before and continued after the change in classification. Despite these uncertainties related to cause-of-death data, our findings indicating a lack of improvement in life expectancy at advanced ages are based on Dutch total mortality rates. Total mortality rates in The Netherlands are considered to be very reliable even for the oldest-old age groups,19 because mortality and population data are derived from municipal population registers that have been kept in The Netherlands since 1850.22 At birth a personal card based on the birth certificate is made and all changes in vital status, including death, are recorded on this card. This guarantees a high validity of age recording and since population registers not only provide data on mortality, but also on the population at risk by single year of age and sex, a single source is used to estimate mortality rates, which avoids biases.
Moreover, differences in the contribution of each age group to the change in life expectancy (based on the Arriaga method) and changes in age-specific mortality rates (based on the CMF method) merit attention. The outcomes of both methods might not always lead to the same conclusion. Comparison of the contribution of different age groups to the change in life expectancy (Arriaga) and the standardizd mortality rates (CMF) by 10-year age groups shows that although the direction of the effect is the same, its relative importance can differ. For a full understanding of the changes in mortality, information derived from both approaches is needed. To explain changes in life expectancy, which was the primary focus of this paper, the Arriaga method is the most appropriate of the two, because, like life expectancy, it takes into account the fact that changes in mortality in different age groups affect life expectancy to a different extent. The magnitude of the effect depends upon the size of the population in a certain age group being exposed to the (changed) mortality rate and the remaining life expectancy of this age group. On the other hand, changes in age-specific mortality rates provide more insight into changes in the age structure and size of the elderly population. In addition, looking at changes in age- and cause-specific mortality rates is indispensable to discovering possible determinants of the changes in mortality.
Studies for other low mortality countries have found no rises in mortality in the oldest old.6,11,18 Only in Norway did mortality at advanced ages increase slightly between 1986/90 and 1991/94.33 Explanations for the recent rise in old-age mortality in The Netherlands (and Norway) are still being sought. More research on this topic is needed. As a start, we will elaborate on possible explanations for the recent rise in old-age mortality in The Netherlands. First, the increase in old-age mortality might have been caused by excess mortality due to influenza epidemics in 1989/90 and 1993.34,35 This is not likely, however. In 1975 and 1978, influenza also produced substantial excess mortality34 without seriously interrupting the mortality decline among the oldest old. In addition, our results are not very sensitive to annual perturbations due to influenza epidemics, for we used quinquennial data. Second, the alleged liberalization of euthanasia policy could have brought forward the average age at death. However, considering the low frequency of physician assistance in death at advanced ages (only 1.8% [1.32.5%] of all deaths above age 80) and the estimated small decrease in the length of life due to euthanasia (less than one week in 76% of these cases),36 we do not consider euthanasia a significant factor. Third, the increase in mortality from (lung) cancer and COPD among the oldest old suggests that (past) smoking behaviour might have contributed to the increase in mortality. A reconstruction of smoking prevalence by birth cohort37 showed that the percentage of (ex)smokers in men aged 85 was probably higher in 1990/94 than in 1980/84. However, although past smoking behaviour might have played a role, the evidence is not conclusive. After all, this factor cannot explain the increase in female mortality at advanced ages, as the percentage of (ex)smokers aged
85 was too small to have had a significant effect on old-age mortality.
The causes discussed so far cannot fully explain the increase in mortality at advanced ages and thus we should consider other causes, such as those relating to changes in the distribution of morbidity and frailty in the population. Less selection due to decreased mortality may have produced a frailer oldest-old population.38 The subsequent increase in mortality from mental disorders, ill-defined conditions and influenza/pneumonia might be a manifestation of this increased frailty. In addition, decreased mortality from circulatory diseases might have created a pool of people with circulatory diseases, who run a higher risk of developing severe stages of these diseases and dying from them.39,40 Finally, reduced mortality from circulatory diseases might have increased the prevalence of diseases that share the same risk factors or are themselves a risk factor for circulatory diseases, such as some cancers or diabetes mellitus. Although it is plausible that these factors have contributed to the increase in old-age mortality, it is not clear why these mechanisms, which may be expected to operate in other countries as well, have not (yet) caused old-age mortality to rise in these countries.
Further investigation into the determinants of the old-age mortality is necessary and may benefit from empirical data on the current developments in old-age mortality in The Netherlands and other low mortality countries. Monitoring of old-age mortality and cross-national comparisons should therefore receive high priority. In addition, an important, but in terms of data requirements very demanding step, would be to disentangle the changes in incidence, disease progression, and fatality of chronic diseases which have caused the mortality increases in the oldest old in The Netherlands.
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Acknowledgments |
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