18. The expanding frontier of survival
The maximal age attainable by man is naturally a matter of great interest and has been the subject of speculation ever since the classical era. Without entering this time-honoured and extremely wide field of literature we shall mention only a few carefully reasoned estimates based on reliable cases. Extrapolating his data on four European countries with reliable information, the French demographer Paul VINCENT (1951) set the maximal age under the circumstances then present, at 110, and Françoise DEPOID (1973), using the same method but newer data, at 117 for men and 119 for women. OLSHANSKY et al. (1993) considered that there is no indication that humans are capable of living much past the age of 110. DUCHENE and WUNSCH (1988) considered that the intrinsic aging process leeds to a maximal life span of 115 years. Other, equally serious estimates have arrived at ages 125 - 130. The maximal age attainable depends closely on the trajectory of the mortality curve at extremely high ages which is the subject of another monograph in this series by THATCHER et al. (forthcoming).
The highest so far known and properly verified case of longevity is that of Jeanne Calment (subject of a book by ALLARD et al., 1994) who was born on 21 February 1975 in Arles, France. Her age was verified from official documentation in loco on her 120th birthday by B. Jeune, J. Vaupel and this author.
The remarkable decline in old age mortality inevitably raises the question of what can be expected in the future. Answers will be sought in the following by calculating what effects a continuing mortality decline would have on the oldest-old population.The effects will be measured in terms of stationary population and the calculations do not constitute actual population projections which would have to be geared to observed age distributions which are historical results of events and influences which the populations in question have lived through in the past 100 years or so. In the countries of our database, the history has by no means been uniform.
An actual projection would require assumptions regarding the annual inflow of 80-year-old to the oldest-old population. The application of the stationary population concept assumes this flow to be constant. In the actual countries, it will tend to rise for some time though with fluctuations due to shortfall of births during World War I and losses in male cohorts incurred in World War II. In the longer run, the increases will generally slow down or stop, different countries evolving in their separate ways. It was, however, demonstrated in Chapter 17 that at ages 100 and over - the true frontier of survival - the growth in numbers does not depend to any great extent on what happens before age 80.
The basic assumption for the forward calculations which will follow is that the recent decline in oldest-old mortality will continue. Using the mortality decline observed between 1960-70 and 1980-90 inthe thirteen countries with best information as standart, we measure the changes in stationary population which will result if this decline is repeated one, two or three more times. These shall be called Scenarios 1,2 and 3. With mortality change we shall understand the relative change in annual agespecific probability of dying (No. 1 of the seven mortality change indicators in Chapter 16) because a constant decline per population-at-risk would soon lead to negative mortality. The resulting q values are given in Table 38.
The mortality decline of the last two decades which is used as standard, accounted among men to an annual reduction of 0.95 percent at age 80, gradually slowing to 0.64 percent at age 100. Among women, the progress at 80 was twice as fast, 1.84 percent and slowed down by age 100 to approximately the same 0.64 as for men.
No time frame is imposed for the scenarios. If the development continues at the same pace during the last two decades, the scenarios will take 20, 40 and 60 years respectively to unfold. If the decline accelerates or slows down, they will simply be realized in either less or more time.
Projection of past change into the future ignores the possibility of fundamental breakthroughs in science which might profoundly reduce the mortality from specific causes or slow the process of senescence. It also ignores the possibility of deteriorating environment with adverse effects on health as well as that of possible appearances of new diseases or more virulent strains of existing ones.
It is very common in population projections to give pride of place to alternatives where ongoing changes in demographic parameters will run their course in a short period and give way to constant rates. Such caution does not seem to be called for regarding the oldest-old today. The decline has gathered strong momentum, the considerable international differences have so far not narrowed and large inequalities in death rates have been found to exist between social groups in the same country. In a modern state, there is no excuse for the existence of large social inequalities in health and survival which to an increasing extent depend on health-related behaviour: smoking, diet, physical excercise etc. The expectation is that people will continue to improve their chances of survival by modifying their lifestyle accordingly and by taking advantage of improvements in medical and public health practices. There is of course no certainty that they will do so and powerful special interests are at work to prevent some aspects of it.
Of the successive scenarios, No. 1 can be considered very likely, in fact almost assured since it is already well underway from its central point 1985 and, according to all indications, mortality decline is continuing. Scenario 2 may also be considered realistic while Scenario 3 is more uncertain based as it is on age-specific death rates so low that their plausibility may be questioned.
The depth of the mortality transformation under the various scenarios can be seen in the first lines in Table 39. Scenario 1 implies mortality reductions of 12 - 17 percent for men and 12 - 31 percent for women which translate into mortality shifts of 2.1 and 2.7 years respectively. Thus, while the scheduled mortality reductions are much larger for women than men, they cause age shifts of more equal size and are, therefore, in a sense, equally deep-going.
A second repetition of the last 20 years' development would lead to death rates up to one-third lower for men and one-half lower for women than the most recent ones. The third scenario would reduce the death rates of 80-year-old women to only one-third of the present level - the likelihood of this to happen may be questioned. In the same scenario, persons of 86-87 years of age would be subject to the mortality of today's 80-year-old. So large an age shift which would be an expression of a commensurate delay in aging would be easily noticeable by people in their daily lives.
Another indicator, the modal length of life, i.e. the most common age at death would increase almost exactly in step with the age shift and, in females, would surpasss 90 years.
The probability of surviving from age 80 to 100, at present still very small, would grow for each sex by a factor of 7 or 8, thereby approaching 5 percent for men and surpassing 10 percent for women.
Life expectancy at age 80 would increase under these conditions but less than spectacularly for males from 6.25 to 9.05 and for females from 7.80 to 12.14 according to Scenario 3. How much would this increas contribute to life expectancy at birth, would depend on what proportion of the newborn survive to age 80. In 1986-88, these proportions were in France 0.37 for males and 0.63 for females. If we apply the ratio 0.5 to males and 0.7 to females - levels that may be reached in some countries early in the next century - the benefits are modest: in the last scenario 1.40 and 3.04 years would be added to the life expectancy of newborn boys and girls respectively.
If and when survival to age 80 increases, the gains are compounded. Under the quite extreme assumption that the last 20 years' decline is repeated, no less than five times - corresponding to 100 years of mortality decline at present speed - the female life expectancy at age 80 would increase to 14.84 years or a full 7 years more than at present. The eradication of all mortality before age 80 would give to newborn girls a life expectancy of 94.8 years.
Next in Table 39, we give the prospective percentage gains in years to be lived at various ages in a stationary population. The relative gain in life-years that can be expected from further mortality decline is quite modest in low eighties but progressively greater in the older age groups reaching a tenfold growth in centenarians - and this without any increase in numbers reaching 80. The overall gain would be larger for females because of their older age distribution.
A striking similarity between male and female growth percentages may be noted at all ages in all scenarios.
The last group of numbers in Table 39 gives the actual years of life to be gained under the different scenarios. In contrast to the relative gains which rise exponentially with age, the absolute gains accrue mostly to ages between 85 and 95 and are much larger for women than men. The phenomenally high growth rates of the oldest have a relatively modest impact because of the low base values. The number of centenarians might be multiplied by ten but it still would not make them a large population group. Even according to Scenario 3 they would make up only 1.4 percent of the males and 2.5 percent of the females at ages 80 and over (figures not shown in the table). They would constitute less than one percent of the total population but they would not be rare cases as they are today.
The message of these conditional results is that further decline in oldest-old mortality would profoundly affect not only the size but also the characteristics of the aged population. Aging, as reflected in mortality, would be significantly delayed.
Gains to be made in life-years would be differential by age so that (a) measured against lives now lost they would be greatest among the youngest but (b) measured against present lifetimes they would be largest among the oldest while (c) measured against an individual's life course or in a stationary population, they would be greatest between ages 85 and 95. It must be added, though, that any reduction of death rates before age 80 would be felt more at age 80 than later and would thus possibly alter the balance of the gains.
For a closer look at what might be called the dominion of death, in Figure 37, the survival curve has been inverted so that years lived are counted from the top. It constitutes the dividing line between life and death for those who reached age 80. If the corresponding lines for the three scenarios were shown, each one would be a little farther to the right but other differences would not be very obvious. We have therefore shown the putative gains in life-years at the bottom. The largest gains for both sexes (of which only the female is shown) always fall to ages slightly below 90. The present dominion of death would be quite significantly reduced at ages 80 to 85 but the inroads to be made into it at highest ages would be minor indeed. Decline of mortality before age 80 would accentuate this feature. A corresponding figure for males would be essentially similar.
Regarding methodology, a note may be appropriate here. The exercise seems to justify the most commonly used approach in projections, namely that of observed relative sex-age-specific change - which may be modified so as to alter the speed or gradually to stop it - as a valid and reasonable way to project future mortality. A time frame is not essential when dealing with a stationary population. In this case, the repetition of an observed 20-year change one, two and three times gave results which were internally consistent.
A further mortality decline from the present level would produce a large age shift but this would not be matched by an equal increase in life expectancy. In the third scenario, the age shift for males would be 6.2 years but the gain in life expectancy only 2.8 years. For females the corresponding figures would be 7.0 and 4.3 years.
Unless scientific breakthroughs occur, the extension of human life will meet resistance in the aging process which, even when pushed back, ultimately prevails.
Updated by V. Castanova, 1 November 1999