The definition of epidemiology as the study of the causes of disease in human population is based on two main concepts: population and disease. This paper discusses these concepts as perceived by epidemiologists. It also discusses the life-style theory as the disease causation theory that guides modern epidemiological studies. The paper emphasizes the instrumental aspect of disease concepts and of causation theories, and discuss the relationship between epidemiology and public health, and between epidemiology and social sciences. This paper points that disease do not have a cause but mechanism of production. The production of disease is a result of genetic determined organic responses to environmental exposures. The cause is a choice of some aspect of this mechanism.
Life style; epidemiology; theory of causation