Ageing and disease.

The concept of disease has a long and changing history, and has accumulated implications that can be unhelpful. The traditional distinction made between 'normal ageing' and 'disease' identifies research into the impact of an ageing population as having arisen within clinical medicine with its tradition of dichotomous thinking. The model is inappropriate for clinical practice among the elderly where diseases should be relegated to the role of mechanisms producing functional problems, and where interventions may not be of the traditional medical form. In this context the concept of 'normal ageing' can act as an excuse for inaction. For gerontological research the basic model is of the interaction between extrinsic and intrinsic factors. We lack the means at present to identify intrinsic processes, although they may be found among the residual ageing effects when extrinsic processes have been excluded. Intrinsic ageing processes may ultimatedly be identifiable on the basis of biological theory. Until this is possible we should study age-associated phenomena without prematurely conceived notions about their origins.