While demographers calculate the steady increase in life expectancy and debate
with biologists on the maximal human life span, gerontologists try to improve
their understanding of the complex mechanisms involved in the aging process,
a phenomenon that began with the origin of life about 3.5 billion years ago.
Aging corresponds to the accumulation of diverse deleterious changes over
the time throughout the cells and tissues which progressively impair function
and can eventually cause death (1).
But, as Robert BUTTLER said “we still don’t know
how to define aging per se” (2).
Several reasons explain the lack of a single definition of aging:
- Aging changes can be attributed to many events, namely: genetic defects, developments, diseases, environmental factors, and an even inborn process, the aging process (1). Aging can be considered from different levels, according to molecular, cellular, morphological, physiological, behavioural and social changes (3).
-
Moreover, there are important variability
and inequalities in the experience of aging and being old. People enter in the
last decades of their life span with the health disadvantage of past
experiences accumulated throughout their life course. There are clear
gradients of ill health in older persons according to the socio-economic
position measured at different time (in mid-life, in early retirement, or in
late life, when entering in institution) (4).
-
In the study of aging and
mortality, a number of issues are related to inter-individual variability and
the search for their solution can lead to a highly complex approaches (5).
Why aging
occurs, and why it develops in one way and not in another one, is a
longstanding enigma on the role of senescence in nature. Even after half a
century of progress, the elucidation remains unfolded. Evolution theory argues
strongly against programmed aging, suggesting instead that organisms are
programmed for survival, not death (6). Recent evidences from disciplines as
diverse as molecular genetics, biology, clinical epidemiology and demography,
provide a direct support to the validity of many of this assumption. So, time
is ripe to re-examine the proposed and sometimes conflicting theories about
aging and to rethink the scientific foundations of the field (7). Aging
appears today more like a general output due to almost all the biological,
social and stochastic factors involved in the life course.
The aim of
this paper is to illustrate this complexity through examples retrieved from
the literature at different levels from genes to individuals in the daily life
and dealing with four families of factors associated with aging: Firstly
genetics, Secondly oxidative metabolic damage, Thirdly pathology and risk
factors, and eventually functioning and disability in the daily life (8). In
addition we provide some examples of links and interactions between
metabolism, pathology and functioning in aging (8). Doing that we keep in mind
that the ultimate goal of gerontologists would be to slow down aging
indefinitely and in parallel to enhance the human well being, as stressed by
the 2010 health report (9).