For many years, health was defined merely as the absence of disease. However, it has become clear that health is an active process that depends on the supportive interaction of all the body's systems. Reflecting this concept, the World Health Organization (WHO) defines health as "the state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity." Many groups, such as the American Public Health Association, Worksite Health Promotion, and the National Wellness Association, have expanded the concept of health further to encompass wellness: the spiritual, social, mental, physical, and occupational needs for one to live life to the fullest.

The World Health Organization defines health as "the state of complete physical, mental, and social wellbeing and not merely the absence of disease or infirmity."
The World Health Organization defines health as "the state of complete physical, mental, and social wellbeing and not merely the absence of disease or infirmity."

In either sense, health is a state of action that includes prevention, care, and individual responsibility to achieve optimal health. The U.S. Department of Health and Human Services (HHS), in Healthy People 2010, divides the ten leading factors affecting health into two major themes. The first, lifestyle challenges, includes physical activity, avoidance of excess weight and obesity, abstinence from tobacco use or substance abuse, and responsible sexual behavior. The second, system enhancement challenges, include mental health, freedom from injury and violence, good environmental quality, immunization, and equal access to health care.


The state of health reflects the body's homeostasis, its attempt to maintain a relatively stable internal environment while confronted with changes in the external environment. One's ability to handle stress depends on the body's success in maintaining or returning to homeostasis. Failure to do so can result in abnormal function and disease.

Homeostasis involves negative feedback systems. The analogy to home heating and cooling systems is often made. When a house falls below a certain temperature, the system turns on to heat the house back to the set level. If it gets too warm, another system effects a change to cool the home off. Similarly, the human body senses changes from ideal conditions in variables, such as blood glucose , dehydration, blood calcium, carbon dioxide, heart rate, breathing rate, and fat deposition. The body also detects the presence of pathogens that alter homeostasis. When such factors disturb homeostasis, the body releases substances such as hormones , neurotransmitters , and antibodies to return conditions to normal.

Why is health important? The WHO states that it is fundamental to world peace and security as political strife can stem from inadequate food, medicine, or other resources. For the United States and other industrialized nations, the large increase in the older population calls for strategies to increase the number of quality years as people age. Living longer is not a positive goal if it means living longer with disease. HHS has made this one of two major goals in Healthy People 2010. The other is to eliminate disparities in health based on race or ethnicity. Too many segments of American society are not reaping the benefits from advances in medicine, technology, and health care.

Individual choices are important to health outcomes. Preventive medicine includes stress reduction, good nutrition, exercise, wearing seat belts and helmets, and having routine dental and physical screenings (for cholesterol level and blood pressure, for example). As science progresses in genetic engineering, important choices will be made about changing genes, thus altering the inheritance of many diseases.

SEE ALSO Alcohol and Health ; Cardiovascular Diseases ; Disease ; Environmental Health ; History of Medicine ; Homeostasis ; Public Health Careers ; Sexually Transmitted Diseases ; Smoking and Health

Karen E. Jensen


Donatelle, Rebecca J. Health: The Basics. Boston: Allyn and Bacon, 2001.

National Institutes of Health. <> .

World Health Organization. <http://www.who> .

The National Institutes of Health (NIH) is one of eight health agencies of the U.S. Public Health Service. The NIH was founded in 1887 with the goal to acquire new knowledge to help prevent, detect, diagnose, and treat diseases and disabilities. As one of the world's fore-most medical research centers, the NIH conducts research, supports research elsewhere, helps train researchers, and fosters communication about medical and health sciences information.

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