Centenarians

Several research teams have attempted to estimate the prevalence of centenarianism, that is, the proportion of the population who are one hundred years and older. Since the number of centenarians is growing much faster than the total population, the prevalence of centenarianism will likely increase in the coming decades. Among the population-based studies with rigorous age verification conducted in the 1990s, the prevalence ranged from 38 per million total population (in Sweden) to 135 per million (in Sardinia). Census-based studies give larger prevalences, but there are concerns that, at these extreme ages, the census data may not be accurate.

These data are all from Western nations. The limited population-based data from other countries suggest that centenarian prevalence is much lower in non-Western nations. This will likely change as these countries experience the demographic shift that has already occurred in the West, the transition from predominantly young to predominantly older populations.

Mortality rates increase exponentially with age; that is, one's chance of dying is higher in each successive year of one's life, and the rate of increase also rises each year. This is known as the Gompertz Law of Mortality. Centenarians, however, do not comply with this law. At around age ninety the rate of increase seems to slow, and at age 110 mortality rates actually decline. Figure 1 illustrates this. Note that the y-axis is logarithmic. The black line is the exponential increase predicted by the Gompertz Law. The red line is the actual observed data, from Japan and western Europe. The blue line is the equation that best fits the mortality data at all ages; the green line provides the best fit for those 105 and older.

Figure 1 Age trajectories of death rates. SOURCE: Vaupel, J. W.; Carey, J. R.; Christensen, K.; Johnson, T. E.; Yashin, A. I.; Holm, N. V.; Iachine, I.A.; Kannisto, V.; Khazaeli, A. A.; Liedo, P.; Longo, V.D.; Zeng, Y.; Manton, K. G.; and Curtsinger, J. W. "Biodemographic Trajectories of Longevity." Science 280 (1998): 857.