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.
Health psychology is the study of psychological and behavioral processes in health, illness, and healthcare. It is concerned with understanding how psychological, behavioral, and cultural factors contribute to physical health and illness. Psychological factors can affect health directly. For example, chronically occurring environmental stressors affecting the hypothalamic–pituitary–adrenal axis, cumulatively, can harm health. Behavioral factors can also affect a person's health. For example, certain behaviors can, over time, harm (smoking or consuming excessive amounts of alcohol) or enhance health (engaging in exercise). Health psychologists take a biopsychosocial approach. In other words, health psychologists understand health to be the product not only of biological processes (e.g., a virus, tumor, etc.) but also of psychological (e.g., thoughts and beliefs), behavioral (e.g., habits), and social processes (e.g., socioeconomic status and ethnicity).
Psychology is the science of behavior and mind, including conscious and unconscious phenomena, as well as feeling and thought. It is an academic discipline of immense scope and diverse interests that, when taken together, seek an understanding of the emergent properties of brains, and all the variety of epiphenomena they manifest. As a social science it aims to understand individuals and groups by establishing general principles and researching specific cases.
The great shift … is the movement away from the value-laden languages of … the “humanities,” and toward the ostensibly value-neutral languages of the “sciences.” This attempt to escape from, or to deny, valuation is … especially important in psychology … and the so-called social sciences. Indeed, one could go so far as to say that the specialized languages of these disciplines serve virtually no other purpose than to conceal valuation behind an ostensibly scientific and therefore nonvaluational semantic screen.
Thomas Szasz, Anti-Freud (1990), p. 44
You must all advance by taking good care of your health. Only by taking good care of your health, you can gain success. The fact is that if your health is not good, how can you do your service? Taking care of your health is as important as any of the other duties of your life. It is your duty towards your body. If your body does not work, how will you function and advance?
Haidakhan Babaji, The Teachings of Babaji, 9 January 1984.