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Human longevity, individual life duration, and the growth of the oldest-old population

Montpellier, 23-25 October 2000

Abstracts of communications

Patterns in Mammalian Aging: Demography and Evolution
Steven N. Austad, university of Idaho, Moscow, USA

Evolutionary theory provides a coherent conceptual framework for understanding the diversity of aging rates in nature. unfortunately, our knowledge about the form or extent of aging in natural populations is limited by technical problems of monitoring large populations of animals throughout life. The limited knowledge we do have, however, is sufficient to conclude that contrary to earlier hypotheses, measurable aging does occur in the wild. Furthermore, natural life spans in excess of two centuries have now been documented in mollusks, fishes, and mammals. Humans are by no means the longest lived animals. Demographic on captive mammal populations are surprisingly sparse, but allow the following conclusions: (1) large mammal species are typically longer-lived than small species; (2) certain taxonomic groups such as bats, primates, and monotremes are exceptionally long-lived for their body size; (3) within a species, a rough trend exists for genetically smaller individuals to live longer than large individuals; (4) female mammals usually, though not universally, live longer than males. The demography of laboratory rodents has been exceptionally thoroughly documented, particularly with inbred strains in which all individuals are genetically identical. This allows us to ask whether there is evidence for biological compression of mortality associated with longer life, while controlling environmental and genetic variation to an extent impossible for humans. An investigation of four mouse and three rat genotypes under standardized conditions, found that caloric-restriction extended mean longevity in all genotypes from as little as 11 to as much as 54%. Longer life in the calorically-restricted groups is not associated with a universal reduction in variation in age-at-death (as measured by coefficient of variation). In mice, mortality was compressed in 7 of 10 cases, whereas in rats mortality was expanded in 6 of 8 cases. Clearly there is no biological necessity for longer life to be associated with mortality compression at least in laboratory rodents.

Mortality at Extreme Ages and Data Quality : The Canadian Experience
Robert Bourbeau and Bertrand Desjardins, université de Montréal, Canada

Recent studies point to a lower old age mortality in North America, but a shadow is cast over them because of uncertainties in data accuracy. Results from the first stage of a study aiming to verify Canadian data, focusing on the validation of data from Quebec for the 1985-1999 period on the basis of parish registers, are presented. They suggest that Quebec data on age at death is very good, at least among Catholic French Canadians. A measurement of mortality at very old ages for Quebec is proposed and compared to some European countries and to Japan. This comparison gives more support to the existence of a North American mortality pattern, characterized by a lower mortality among the oldest-old.

Life Span Extension in Humans is Self-reinforcing: A General Theory of Longevity
James R. Carey and Debra S. Judge, university of California, Davis, USA

We propose that longevity is not merely the result of an absence of mortality but a self-reinforcing and positively selected life history trait in social species. We develop the argument that a small increase in longevity is amplified as (1) reductions in mortality at young ages increases natural selection for mechanisms of maintenance and repair at all older ages as well as increasing the potential for intergenerational transfers; (2) intergenerational transfers of resources from old to young increase fitness (e.g. through improved health, skill, and competitive ability) of the young and thus favor the presence of older individuals in a population; and (3) the division of labor increases both efficiency and innovation at all levels resulting in increased resources that can be invested. This is a theory framed around the longevity-oriented question posed two decades ago by George Sacher "Why do we live as long as we do?" rather than the more prevalent question today "Why do we age?" We describe the foundational principles and the main phases of our model for the evolution of longevity mediated through social organization and apply the concept specifically to human populations.

Explanation of the Decline in Mortality among the Oldest-old: a Demographic point of view
Graziella Caselli , Department of Demography, university of Rome "La Sapienza"
James W. Vaupel, Anatoli I. Yashin, Max Planck Institute for Demographic Research, Rostock

In many highly developed countries, remarkable progress has been made in recent decades in reducing death rates, especially at older ages. New statistical data on mortality over time and up to the highest ages have revealed the time and age pattern of these improvements. These data have permitted reliable estimation of the age-trajectory of mortality, which turns out to follow a logistic pattern with deceleration at advanced ages. Individuals are heterogeneous with regard to their chances of death, and the frail tend to die first. Deeper understanding of the age-trajectory of mortality and the pattern of mortality improvements hinges on the development of statistical models that incorporate such mortality selection. This paper surveys the dynamics of mortality over age and time, reviews some "frailty model" approaches to analyzing these dynamics, and presents some illustrative findings from studies of Danish twins and of the surface of Italian mortality over age and since 1895. Our goal is to participate in the debate on longevity from a demographic point of view and disclose the underlying features of accelerating human longevity. We are of the opinion that an analysis of this nature could help reveal the triggering factors. The study is a first step towards achieving this goal.

Genetic Factors Associated with Individual Life Duration: Heritability
Kaare Christensen, Odense university, Denmark
Anne Maria Herskind, Odense university Hospital, Denmark

Heritability is defined as the proportion of the total variance in a population that is attributable to genetic differences between individuals. Hence, a high heritability for a trait indicates that a large proportion of the individual differences in the trait is caused by genotypic or allelic differences, while a low heritability suggests that the reasons for the phenotypic differences are primarily to be sought in differences in environmental exposures or in stochastic processes. In this way heritability estimates are useful in pointing towards the potentially most fruitful research directions.

The current evidence based primarily on Nordic contemporary populations suggests that approx. a quarter of the variation in adult lifespan can be attributed to genetic factors, i.e. the heritability of lifespan is about 25%. The age-specific susceptibility to death (’frailty’) has a heritability of about 50%. The available twin data suggest that the genetic factors affecting lifespan are acting non-additively, i.e. the effect of various gene variants depends on other gene variants.

Importance of the age group choice in the analysis of the family component of longevity
Amandine Cournil, université de Lyon, France

Various gender effects on the resemblance between parents and offspring for their life span have been reported in the literature. A review of the different studies suggested that a part of the inconsistency in the results might be explained by the choice of different age groups for the offspring sample. This hypothesis was tested on a sample of 811 families coming from a French rural region during the 18th to 20th centuries. The results showed that the gender pattern in the familial resemblance was indeed influenced by the sampling of the age group for the offspring generation. The general trend observed was a weak father-daughter resemblance when early mortality is taken into account and a larger resemblance between parents and daughters than between parents and sons when later mortality (above age 50) was analysed.

Marital status and family support for the oldest old in Great Britain
Emily Grundy and Michael Murphy, London School of Hygiene and Tropical Medicine

In this chapter the authors present projections of the marital status distribution of the oldest old population and of the proportion of women with no, one or two surviving children under various mortality assumptions. These show the extremely favourable position of those attaining oldest old ages in the next twenty years and the much less favourable longer-term prospects. The influence of marital status on living arrangements, including transitions to institutions, and on perceived social support is analysed in the second half of the chapter. Results suggest that changes in marital status composition will have major implications for the well being of the oldest old population and on the demand for long-term care.

Causes of Death among the Oldest-Old: Distributions and Age Variations
Shiro Horiuchi, Rockefeller university, New York

Although death rates from most degenerative diseases increase with adult age, they follow significantly different age trajectories. Thus the cause-of-death distribution among the elderly changes notably with age. This analysis of U.S. mortality data shows that the cause-of-death structure at younger old ages is dominated by some major diseases such as cancer, myocardial infarction, and cirrhosis. However, various causes that are uncommon at younger old ages become increasingly common at older old ages, thereby diversifying causes of death at older ages. Those causes include septicemia, nutritional deficiency, anemia, mental disorder, pneumonia, influenza, peptic ulcer, skin disease, accidental fall, and inhalation and ingestion accident. This diversification seems to reflect the old-age frailty: the general ability to maintain homeostasis declines with age, making the oldest-old highly vulnerable to various kinds of physiological stress.

Explanation of the decline in mortality among the oldest old: a medical point of view
Bernard Jeune, university of Southern Denmark

Despite the complexity of an explanation of the decline in mortality among the oldest-old, it seems reasonable to find an explanation in the declining CVD mortality. A thorough review of the literature on the epidemiology of CVD led to the conclusion that this decline is attributable to a combination of

1. a declining incidence, including a substantial reduction in out-of-hospital deaths, due to improvement of primary prevention, especially in the prethrombolytic period (before the mid-1980s),
2. a declining case-fatality due to improvement of treatment which increased markedly in the thrombolytic period (since the mid-1980s),
3. a declining recurrence rate due to improvement of secondary prevention, mainly in the thrombolytic period.

Although primary prevention is far from exhausted, especially among elderly people, we may also expect an increasing contribution of improvements in treatments and secondary prevention, particularly among the oldest-old.

Social Determinants of Mortality in the Oldest-Old: Social Class and Individual Way-of-Life
Marja Jylhä, university of Tampere, Finland
Tiina Luukkaala, Tampere university Hospital Research unit, Finland

Social factors largely explain differences in life expectancies both between countries and between different groups of population in each countries. Convincing evidence shows that, individual lifestyles, social networks, styles of relating to life, and in particular, social class, are major determinants of mortality at least from childhood to early old age. This literature is reviewed in the first part of the paper. Mainly due to methodological reasons, however, the data on possible social predictors of mortality in the oldest-old is scarce. Some studies suggest that due to the selective mortality earlier in life, determinants of mortality would be different at the late old age (the "crossover" phenomenon). In the TamELSA Study we examined mortality during 10 years in a population aged 80-89 years at baseline. Adjusted for age, gender, and health status, both not taking physical exercise and, in particular, low level of social participation, were significant predictors of mortality. Social class showed a suggestive, but not significant association. Our study indicates that same social factors found to be important at younger ages also predict mortality in the oldest-old, although the association may be weaker.

Central and dispersion indicators of individual life durations : new methods
Vanö Kannisto, Max Planck Institute for Demographic Research, Rostock

The life expectancy at birth can be complemented by late life mode which imparts relevant and valuable information that the former fails to give. For the dual phenomenon of compression of mortality and rectangularization of the survival curve it is proposed to measure each one separately by an unambiguous indicator : compression by a set of C-indicators which give the shortest age interval in which a given proportion of all deaths occur, and rectangularity by a set of R-indexes which give the proportion under survival curve in a rectangle cut off at the point where 0.01 of the original population is still alive. Applied to a wide variety of situations they give consistently a firm and precise answer to the question whether these phenomena are taking place.

Marital status and family support for the oldest-old in Canada
Jacques Légaré, université de Montréal
Laurent Martel, Statistique Canada

using data from the uNECE/PAu data base on older persons and the Canadian General Social Survey (Cycle 11- 1996), the authors look at the social network around elderly. First, they used data available to establish an age threshold for the oldest-old. For many reasons, seniors aged 80 years and over were in the present study considered as oldest-olds. Among the principal results, living with a spouse shows even at these ages a protective effect. Also, living with others is mostly a way to cope with a lost of autonomy. However, living with others is just the tip of the iceberg in terms of possible help received by the oldest-olds. The social network has an important role. Finally, oldest-olds are not only care-receivers but that one over four is also a caregiver, mainly in a context of shared activities.

Genetic Modulations of Human Life Span: An Overview
George Martin, university of Washington

We consider several classes of gene action that can modulate human life span. Longevity assurance genes evolved as by-products of the need to keep the soma alive for longer periods of development and/or longer periods of active reproduction, in response to new ecological conditions. A second category of "good" genes involves deleterious effects late in the life course, thus escaping the force of natural selection. "Good" genes may also be down-regulated for good reasons, as a response, for example, to the need to cease growth at the time of maturation. But there are also "bad" genes that do not show their true colours until late in the life span, again because those effects escape the force of natural selection. Numerous classes of amyloidosis fall into this category, including the beta amyloid that many believe cause dementias of the Alzheimer type.

Looking for a working definition of frailty
JP Michel, Geneva university Hospital

Clinicians say that they can easily distinguish a FRAIL from a NON-FRAIL older. And, it is true. To do so they use a set of factors such as age (appearance), nutritional status (thin, loss of weight), subjective rating (health perception), level of performance (cognition, fatigue), list of impairments (vision, hearing, strength), current functional status (I.A.D.L., A.D.L.), current use of care (# medications, hospital).

But there is no "working" definition that would assist the identification of this high-risk subset of the population prior to the onset of these adverse outcomes. One major reason is that there is probably not only one kind of frailty, but a variety of possible expressions of frailty: physical, mental, affective, nutritional and sensory. An important problem is to determine which is the first component involved and which is the most important. How is it possible to explain that one single organ dysfunction can precipitate the loss of physiological reserve, preventing the older to cope with stress.

To go ahead putting in operation a definition of frailty it will be necessary to target the objective (population or individual ?), the setting (community or hospital ?) and the purpose (clinical or research ? screening or intervention ?).

However a working definition of frailty will be very useful to identify the older that would be the most likely to benefit of a comprehensive evaluation, preventive interventions and team-based care.

A better understanding of the frailty process is indispensable. A lot of work needs to be done to perfectly differentiate robust ageing to frail process.

Social integration and contribution of the oldest old: a study of the nonagenarians and centenarians of India
P.K.B.Nayar, Center for Gerontological Studies, Kochulloor, Trivandrum, India

The paper gives as background a brief account of the ageing scenario in India and then presents the findings of two identical studies conducted by the author in late 1990s on the 90+ population of Kerala (India). A socio-economic profile of the 90+ including pattern of residence and health, activity and functional disability statuses is given followed by a section on social integration, role and contribution of the subjects. These include respondent’s family role and status, satisfaction with them and with care giving received from family members, family and social network support, respect and importance in the family and attitude to life. Findings include continued prevalence of elder-friendly traditional values and young-old bonds. The old get honourable treatment in the family though the bond with the society decreases with advance of age. Progressively increasing span of life without adequate provision for welfare is contributing a new dimension to ageing in India.

Recent trends in life expectancy and rectangularization of the survival curve at advanced ages in the Netherlands
Wilma J Nusselder, Erasmus university Rotterdam

This study examined the recent developments in old-age mortality in the Netherlands, by looking at life expectancy and compression of mortality in the period 1970/74-1995/99. Our results show that life expectancy at age 60 increased during the whole period, but that in men life expectancy at age 85 declined in the 1980s and 1990s, whereas in women it remained virtually constant. Analyses on compression of mortality, based on Keyfitz’ H and its numerator, indicated that compression of mortality took place in a relative sense during the whole period in women and since 1975/79 in men. Since 1980/84 in both sexes compression of mortality took place in an absolute sense as well. The combination of the increasing life expectancy at age 60 and compression of mortality in an absolute and a relative sense means that rectangularization took place in a relative sense and an absolute sense. During the second half of the 1990s, the lack of increase in life expectancy at advanced ages and the processes of compression of mortality and rectangularization continued.

Rectangularization of the survival curve: an assessment in Switzerland
Fred Paccaud, Institut universitaire de médecine sociale et préventive, Lausanne

Objective: To check if signs of rectangularization of the survival curve appeared during the last decades in Switzerland, i.e., if the life expectancy is approaching a maximum with a clustering of age at death around an average value (the so-called "compression of mortality").

Methods: Descriptive analysis of age of death and its trends over 26 years, as characterised by the modal value, median and various percentiles beyond the median.

Population : All deaths occurring after the 50th birthday in Switzerland between 1969 and 1994 (N=1,390,362).

Main results: The age at death is increasing at a sustained rate at all percentiles equal or greater than 50, without any slowdown in the trend during this period. The increase is more marked among women. Rates of increase are diminishing as the percentiles of age at death are higher, suggesting some clustering of deaths beyond the median value. However, the maximum age at death, if any, seems to be far from the current median values, even for females who enjoy a relatively high median age at death

The Built Environment, Health and Longevity: Multilevel Salutogenic and Pathogenic Pathways
Andrew Wister, Simon Fraser university, Vancouver, Canada

This chapter reviews interdisciplinary literature that investigates the influence of the built environment on a variety of aspects of subjective and objective health status that may improve both the quality and quantity of remaining years of life. We begin with conceptual definitions of longevity, health and the built environment, followed by a discussion of the development, expansion and synthesis of person-environment models and related theoretical frameworks. Salutogenic and pathogenic pathways are identified through which the built environment may influence health, the disablement process, and longevity. These pathways are elucidated by examining key environmental contexts drawn from the literature on relocation, housing characteristics and well-being, the meaning of home, delay of institutionalization, technological devices, falls and other injuries, and healthy communities. It is concluded that the built environment interacts dynamically over the life course with social environments (e.g., social network, neighbourhood and community), and individual adaptive processes. Furthermore, it may act as a medium for health and illness (e.g., clean or contaminated water); function as a stress-reducer or stressor (e.g., design elements of an institutional environment); operate directly as a source of safety or danger (e.g., falls and injury); enable or facilitate health (e.g., assitive technology, home automation, and home health care); and serve as a health resource (e.g., community home support services).

Mortality trajectory of oldest old in China
Zeng Yi, Center for Demographic Studies, Duke university
James W. Vaupel, Max Planck Institute for Demographic Research, Rostock

This paper confirms that the phenomenon that death rates decelerate at oldest old ages found in the developed world also exists in China, a developing country. We tried to fit different relevant models to the Han Chinese mortality rates from age 80 to 109, and found that the logistic model performs better than the other models do. While the male and female Han Chinese mortality rates at oldest old ages are generally higher than the Japanese and Swedish rates, the curves converge and slightly crossover at ages 97 and 98 for males and females, respectively. Based on previous studies on age validation and a comparison with the U.S. black-white mortality crossover, we believe that the convergence of the Chinese mortality rates with Japanese and Swedish ones at ages 97-98 is mainly due to heterogeneity selection. However, it is possible that a marginal proportion of Han Chinese oldest old may inaccurately report their ages; this may also contribute to the convergence.

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