Definition of normal Ageing

Ageing, the process of growing old, is defined as the gradual biological impairment of normal function, probably as a result of changes made to cells (mitotic cells, such as fibroblasts and post-mitotic cells, such as neurons) and structural components (such as bone and muscle). These changes would consequently have a direct impact on the functional ability of organs (such as the heart, kidney and lungs), biological systems (such as the nervous, digestive and reproductive system) and ultimately the organism as a whole.

The following is a description setting out five criteria’s for ageing, as proposed by Strehler (1962).

Cumulative: Effects of ageing increase with time.
Universal: All members of a species display signs of ageing.
Progressive: Ageing is a series of gradual changes.
Intrinsic: Changes would take place even in a “perfect” environment.
Deleterious: Changes which occur compromise normal biological functions.

Like ageing, disease is also defined as an impairment of normal function within a living organism. Since the ageing process leads to biological impairment, it would not therefore be a surprise if some of these age-associated changes manifest themselves as disease. Evidence providing a link between ageing mechanisms and age-related disease development/progression is gradually increasing (discussed at a later date).