If something is a disease then one should try to cure it. However, the question of what is a disease and what is not can be a slippery one, and sensitive to cultural perspective. For example, during much of the last century, gay people were viewed as mentally ill. Our view of ageing-related illness is also subject to such nosological elasticity. It was only in 1977 that late-onset Alzheimer's disease (occurring after age 65) was defined as a pathology, as opposed to the natural senility accompanying the second childhood of advanced old age. Is the logical endpoint of this process of redefining isolated components of the ageing process as pathology to view the entire ageing process as pathological?
Whether ageing should be viewed as a disease or a non-pathological process accompanying disease has been debated since classical times [2
]. Yet from the perspective of modern biogerontology, there is little to distinguish biological ageing from a disease state [3
]. Ageing is a process characterized by a broad spectrum of pathologies the sum of which leads inevitably to death [4
], and its biology by loss of homeostasis and accumulation of molecular damage [1
]. But is this sufficient grounds to consider it a disease?
Human health has been defined in terms not only of absence of disease, but also in terms of the presence of a level of function that is typical of human beings of a given age and gender [5
]. By this view, ageing is a normal process and therefore distinct from disease. Thus, although ageing is characterized by a broad spectrum of diseases, at the same time it is a normal process, and therefore not pathological.
Arguably, this apparent paradox may be resolved by reference to the evolutionary theory of ageing, which provides a biological perspective upon the function and significance of the ageing process [3
]. According to the evolutionary theory, ageing is a consequence of a reduction in the force of selection against mutations with deleterious effects later in life [6
]. This leads to accumulation within populations of alleles with deleterious effects later in life—particularly alleles that also have beneficial effects on reproductive fitness early in life [8
]. The evolutionary theory provides the bleak insight that ageing serves no purpose in terms of fitness, but instead is a lethal genetic disease that afflicts all human beings. Arguably, the significance of the universality of ageing is not that ageing is not a disease, but rather that it is a special form of disease. To argue that ageing is not a disease by virtue of its universality is as misleading as it is to argue that the Basenji is not a dog because it does not bark.
The clinical redefinition of ageing as a disease state would not only make sense, but it would also foster the development of therapies of benefit to older people. For example, it would provide incentive to drug companies to profit by developing effective anti-ageing therapies. It would also help to deter those marketing bogus treatments for ageing, and protect older people from being swindled [9
]. In the USA, for example, the Federal Drug Administration (FDA) is responsible for ensuring the safety and efficacy of medical products at the federal level. Because ageing is not viewed as a disease, orally administered drugs directed against ageing fall under FDA regulations for cosmetic medicine and are, therefore, not subject to same the rigorous testing requirements as other drugs that reduce disease [9
]. Redefinition of ageing as a disease would lead to proper safety and efficacy testing of anti-ageing treatments.