On maximum human life span: interdisciplinary approach about its limits.
BACKGROUND
This is a theoretical approach on the question on how much maximally may extend the life of human individual. The starting point of this work was the biological consideration of two changes in human characteristics which took place during the last century up to now, namely human beings lived remarkably longer and are becoming taller.


METHODS
Demography data and Gompertz deduced mathematics, either related to growth or survival, were the two columns on which the basis of this study has been supported. Respective equations were adapted to the purpose searched applying parameters of. normal body growth and cell growth in vitro. Having individual age on the abscisse, that of its crossing point with ordinate value indicates the age in which no more cell activity should exist, either of proliferation or migration.


RESULTS
Despite rising life expectancy, whose extrapolation leads to remarkable enhance for future values, life span calculations with the help of our mathematic models do not indicate an extent beyond the limit of 120 years. Nevertheless hypothetically there is the exception of prolonging life out of the mentioned limit when growth and ageing would be proportional interrelated. Furthermore, when proliferation results of in vitro smooth muscle cell cultures were related to age of donor, its linear regression crosses the x-axis at an age of 110.16 years (mean value of different procedures of measurement) . This limit is not far from that using other cell activity parameters as migration (117.7 years when cessation) or such state of senescent (98 years when all cells involved). Nevertheless with the help of Gompertz equation putting growth in the ordinate (proliferation activity) instead mortality and donor age in the x-axis, the follow up of the curve is similar to that known of survival up to the age of 80. But this procedure does not seem adequate to obtain information on the limit of life potential because of later this curve becomes very flat reaching the end at age around 180; this seems not to be real but due to an artefact. Finally IGF-1 prolongs the cessation ( x-axis crossing point) of cell growing activity up to donor age of around 126.4 years.


CONCLUSIONS
Human life span seems to be limited up to around 120 years, but growth process modulating factors could theoretically enhance it.
Ruiz-Torres
A
A
University Research Institute of Gerontology and Metabolism, Madrid, Spain. iuigm.hlpr@salud.madrid.org
Beier
W
W
D015415:Biomarkers; D001827:Body Height; D002465:Cell Movement / Q000502:physiology; D049109:Cell Proliferation; D002478:Cells, Cultured; D006801:Humans; D008017:Life Expectancy; D008136:Longevity / Q000502:physiology*; D008962:Models, Theoretical; D032342:Muscle Cells / Q000502:physiology; D013030:Spain
D015415:Biomarkers