Longevity index (LI%) and centenarity index (CI%): new indicators to evaluate the characteristics of aging process in the Italian population.

Centenarians represent a group of population displaying the most rapid expansion. This progressive increase of the presence of centenarians is a multi-factorial phenomenon, which is due to the improvements of the environmental conditions and the life style and also to the progress of the medical science. In order to obtain a more reliable estimate of the longevity per gender and territorial entities, we propose two new indicators. (i) The ratio between the ultranonagenarians and the total population above 65 years old (called longevity index: LI%); (ii) the ratio between the centenarians and the total population above 90 years old (called centenarity index: CI%). An analysis of the data of the Italian National Office of Statistics (ISTAT, ) using these two indicators demonstrates that the subjects above the age of 90 are more frequent in the regions of Central and Northern Italy, which are more developed regarding the economic conditions and technological progress. Nevertheless, the Southern and Insular regions of Italy have a higher occurrence of centenarians among the ultranonagenarian population, and also a higher prevalence of male centenarians, as compared to the northern regions. This demonstrates that achievement of the threshold of 100 years old does not require only particular socio-economic conditions, but also an adequate climate and environment, as well as a favorable genetic composition.