Epidemiology
Epidemiology is the study and analysis of the distribution (who, when, and where) and determinants of health and disease conditions in defined populations.
Health
Health is the ability of a biological system to acquire, convert, allocate, distribute, and utilize energy with maximum efficiency. The World Health Organization (WHO) defined human health in a broader sense in its 1948 constitution as "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity." This definition has been subject to controversy, in particular as lacking operational value, the ambiguity in developing cohesive health strategies and because of the problem created by use of the word "complete", which makes it practically impossible to achieve. Other definitions have been proposed, among which a recent definition that correlates health and personal satisfaction.
Hygiene
Hygiene is a set of practices performed to preserve health. According to the World Health Organization (WHO), "Hygiene refers to conditions and practices that help to maintain health and prevent the spread of diseases." Personal hygiene refers to maintaining the body's cleanliness.
Health
There are more disorders of the mind than of the body, and they are of a more dangerous nature.
Marcus Tullius Cicero, Tusculanae Disputationes (c. 45 BCE), Book III, Section III, p 93, translated by Charles Duke Yonge (1877 edition)
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