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K. CHRISTENSENa & J. W. VAUPELb From abOdense K. CHRISTENSENa & J. W. VAUPELb From abOdense University Medical School, Odense, Denmark; bSanford Institute, Duke University, Durham, NC, USA; and aThe Danish Epidemiology Science Centre, The Steno Institute of Public Health, Department of Epidemiology and Social Medicine, Aarhus University Hospital, Aarhus, Denmark
Abstract. Christensen K, Vaupel JW (Odense University Medical School, Odense, Denmark; Sanford Institute, Duke University, Durham, NC, USA; and The Danish Epidemiology Science Centre, The Steno Institute of Public Health, Department of Epidemiology and Social Medicine, Aarhus University Hospital, Aarhus, Denmark). Determinants of longevity: genetic, environmental and medical factors (Review). J Intern Med 1996; 240: 333–41.
This review focuses on the determinants of longevity in the industrialized world, with emphasis on results from recently established data bases. Strong evidence is now available that demonstrates that in developed
Introduction
The determinants of longevity might be expected to be well understood. The duration of life has captured the attention of many people for thousands of years; an enormous array of vital-statistics data are available for many centuries. Life-span is easily measured compared with other health phenomena, and in many countries data are available on whole populations and not just study samples. Knowledge concerning determinants of human longevity, however, is still sparse, and much of the little that is known has been learned in recent years. This review
countries the maximum lifespan as well as the mean lifespan have increased substantially over the past century. There is no evidence of a genetically determined lifespan of around 85 years. On the contrary, the biggest absolute improvement in survival in recent decades has occurred amongst 80 year-olds. Approximately one-quarter of the variation in lifespan in developed countries can be attributed to genetic factors. The influence of both genetic and environmental factors on longevity can potentially be modified by medical treatment, behavioural changes and environmental improvements.
Keywords: centenarians, life expectancy, lifespan, mortality.
focuses on genetic, environmental and medical factors as determinants of longevity in developed countries and discusses alternative paradigms concerning human longevity.
How should longevity be measured?
Longevity can be studied in numerous ways; key questions include the following. How long can a human live? What is the average length of life? Are the maximum and average lengths of life approaching limits? Why do some individuals live longer than others? In addressing these questions, it is useful to
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study the maximum lifespan actually achieved in various populations, the mean lifespan, and the variation in lifespan. Estimating the maximum lifespan of human beings is simply a matter of finding a well-documented case report of a person who lived longer than other welldocumented cases. The assessment of mean lifespan in an actual population requires that the study population is followed from birth to extinction. An alternative approach is to calculate age-specific death rates at some point in time for a population, and then use these death rates to determine how long people would live on average in a hypothetical population in which these death rates prevailed over the course of the people’s lives. This second kind of mean lifespan is generally known as life expectancy. The life expectancy of the Swedish population in 1996 is the average lifespan that would be achieved by the 1996 birth cohort if Swedish mortality rates at each age remained at 1996 levels for the entire future life of this cohort. Assessment of determinants of life expectancy and variation in lifespan amongst individuals rely on demographic comparisons of different populations and on such traditional epidemiological designs as follow-up studies of exposed or treated versus nonexposed or nontreated individuals. Designs from genetic epidemiology – such as twin, adoption and other family studies – are useful in estimating the relative importance of genes and environment for the variation in longevity.
Determinants of extreme longevity
Numerous extreme long-livers have been reported in various mountainous regions, including Georgia, Kashmir, and Vilcabamba. In most Western countries, including the Scandinavian countries, exceptional lifespans have also been reported. Examples are Drachenberg, a Danish–Norwegian sailor who died in 1772 and who claimed that he was born in 1626, and Jon Anderson, from Sweden, who claimed to be 147 years old when he died in 1729. There is noconvincingdocumentationfortheseextremelonglivers. When it has been possible to evaluate such reports, they have proven to be very improbable [1, 2]. In countries, like Denmark and Sweden, with a long tradition of censuses and vital statistics, remarkable and sudden declines in the number of
extreme long-livers occur with the introduction of more rigorous checking of information on age of death, as the result of laws requiring birth certificates, the development of church registers and the establishment of statistical bureaus [3, 4]. This suggests that early extreme long-livers were probably just cases of age exaggeration. Today (March 1996), the oldest reported welldocumented maximum lifespan for females is 121 years [5] and for males 113 years [6]. Both these persons are still alive. Analyses of reliable cases of long-livers show that longevity records have been repeatedly broken over past decades [3, 6]; this suggests that even longer human lifespans may occur in the future. There has been surprisingly little success in identifying factors associated with extreme longevity. A variety of centenarian studies have been conducted during the last half century. As reviewed by Segerberg [7], most of the earlier studies were based on highly selected samples of individuals, without rigorous validation of the ages of reputed centenarians. During the last decade several more comprehensive, less selected centenarian studies have been carried out in Hungary [8], France [9], Finland [10] and Denmark [11]. A few specific genetic factors have been found to be associated with extreme longevity. Takata et al. [12] found a significantly lower frequency of HLA-DRw9 amongst centenarians than in an adult control group in Japan, as well as a significantly higher frequency of HLA-DR1. The HLA-antigens amongst the Japanese centenarians are negatively associated with the presence of autoimmune diseases in the Japanese population, which suggests that the association with these genetic markers is mediated through a lower incidence of diseases. More recently, both a French study [13] and a Finnish study [14] found a low prevalence of the e4 allele of apolipoprotein E amongst centenarians. The e4 allele has consistently been shown to be a risk factor both for coronary heart disease and for Alzheimer’s dementia. In the French study [13], it was also found that centenarians had an increased prevalence of the DDgenotype of angiotensin-converting enzyme (ACE) compared with adult controls. This result is contrary to what was expected as the DD-genotype of ACE has been reported to be associated with myocardial infarction. Only a few genetic association studies concerning extreme longevity have been published... |