Health is one of the most important aspects of human life and therefore of special concern to individuals, but also the subject of discussion in many disciplines such as biology, medicine, psychology, sociology, anthropology, philosophy, and spiritual schools (religions). Nevertheless, not only today, but throughout history, many experts contributed to shedding light on the questions concerning human health: defining meaning of health, causes of health diminishing and restoring of good health condition.
The term “health” comes from the term "wholeness, being whole”. This means that only the state in which you feel whole, and your body, your mind, your emotions and your energy are aligned and balanced, you can also consider yourself healthy.
This is partly reflected in contemporary health definitions:
According to the World Health Organization (WHO), the health is "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity."
Another definition is derived from evolutionary biology, and measures the state of health with the ability of individual to adapt and manage physical, mental and social challenges throughout life.
While the first definition considers health to be the state in which absolute capacity is attained at every level (physical, mental or social), the second definition considers health as an absolute adaptation to internal and external effects, independent of individual capacity. Although both definitions capture some important meanings of health, they both distinguish between physical, mental and social aspects and are therefore prone to misinterpretations.
Why is the right definition of health important?
Because, the way health and well-being are define and measured affects not only the diagnostics and development of healing treatments, but also how society evaluates and manages individual health condition. It also influences how we assess our health, what we think about our own condition, and how much responsibility we take considering our health condition.
In order to develop the right definition of well-being and heath, we need to understand the intertwining of the physical, mental and emotional aspects and the mutual interactions between and within single individual, nature and society. Nevertheless, we must also recognise that these interactions are much too complex to be assessed, measured and treated only by conventional methods, and that the only measure of well-being that really matters is the extent of personal suffering.
 World Health Organization. Constitution of the World Health Organization as adopted by the International Health Conference, New York, 19–22 June 1946; signed on 22 July 1946 by the representatives of 61 States (Official Records of the World Health Organization, no. 2, p. 100) and entered into force on 7 April 1948. In Grad, Frank P. (2002). "The Preamble of the Constitution of the World Health Organization". Bulletin of the World Health Organization. 80 (12): 982.
 Fitness is measured by level of adaptation of an individual or a genotype to its environment