Health is the level of functional and (or) metabolic efficiency of a living being. In humans, it is the general condition of a person in mind, body and spirit, usually meaning to being free from illness, injury or pain (as in “good health” or “healthy”).^[1] The World Health Organization (WHO) defined health in its broader sense in 1946 as "a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity."^[2][3] Although this definition has been subject to controversy, in particular as having a lack of operational value and the problem created by use of the word "complete", it remains the most enduring.^[4][5] Classification systems such as the WHO Family of International Classifications, including the International Classification of Functioning, Disability and Health (ICF) and the International Classification of Diseases (ICD), are commonly used to define and measure the components of health.

The maintenance and promotion of health is achieved through different combination of physical, mental, and social well-being, together sometimes referred to as the “health triangle”.^[6][7] The WHO's 1986 Ottawa Charter for Health Promotion furthered that health is not just a state, but also "a resource for everyday life, not the objective of living. Health is a positive concept emphasizing social and personal resources, as well as physical capacities."^[8]

Systematic activities to prevent or cure health problems and promote good health in humans are delivered by health care providers. Applications with regard to animal health are covered by the veterinary sciences. The term "healthy" is also widely used in the context of many types of non-living organizations and their impacts for the benefit of humans, such as in the sense of healthy communities, healthy cities or healthy environments. In addition to health care interventions and a person's surroundings, a number of other factors are known to influence the health status of individuals, including their background, lifestyle, and economic and social conditions; these are referred to as "determinants of health".

Determinants of health

Generally, the context in which an individual lives is of great importance on health status and quality of life. It is increasingly recognized that health is maintained and improved not only through the advancement and application of health science, but also through the efforts and intelligent lifestyle choices of the individual and society. According to the World Health Organization, the main determinants of health include the social and economic environment, the physical environment, and the person's individual characteristics and behaviors.^[9]

More specifically, key factors that have been found to influence whether people are healthy or unhealthy include:^[9][10][11]

An increasing number of studies and reports from different organizations and contexts examine the linkages between health and different factors, including lifestyles, environments, health care organization, and health policy - such as the 1974 Lalonde report from Canada^[11]; the Alameda County Study in California^[12]; and the series of World Health Reports of the World Health Organization, which focuses on global health issues including access to health care and improving public health outcomes, especially in developing countries.^[13]

The concept of the "health field", as distinct from medical care, emerged from the Lalonde report from Canada. The report identified three interdependent fields as key determinants of an individual's health. These are:^[11]

• Lifestyle: the aggregation of personal decisions (i.e. over which the individual has control) that can be said to contribute to, or cause, illness or death;
• Environmental: all matters related to health external to the human body, and over which the individual has little or no control;
• Biomedical: all aspects of health, physical and mental, developed within the human body as influenced by genetic make-up.

Focusing more on lifestyle issues and their relationships with functional health, data from the Alameda County Study suggested that people can improve their health via exercise, enough sleep, maintaining a healthy body weight, limiting alcohol use, and avoiding smoking.^[12]

The environment is often cited as an important factor influencing the health status of individuals. This includes characteristics of the natural environment, the built environment, and the social environment. Factors such as clean water and air, adequate housing, and safe communities and roads all have been found to contribute to good health, especially the health of infants and children.^[9][14] Some studies have shown that a lack of neighborhood recreational spaces including natural environment leads to lower levels of personal satisfaction and higher levels of obesity, linked to lower overall health and well being.^[15] This suggests the positive health benefits of natural space in urban neighborhoods should be taken into account in public policy and land use.

Genetics, or inherited traits from parents, also play a role in determining the health status of individuals and populations. This can encompass both the predisposition to certain diseases and health conditions, as well as the habits and behaviors individuals develop through the lifestyle of their families - also referred to as the "nature versus nurture" debate, in other words the role of factors which can or cannot be controlled. For example, genetics may play a role in the manner in which people cope with stress, either mental, emotional or physical.

Maintaining health

Achieving and maintaining health is an ongoing process, shaped by both the evolution of health care knowledge and practices, as well as personal strategies and organized interventions for staying healthy.

Role of science in health

Health science is the branch of science focused on health. There are two main approaches to health science: the study and research of the body and health-related issues to understand how humans (and animals) function; and the application of that knowledge to improve health and to prevent and cure diseases and other physical and mental impairments. The science builds on many sub fields, including biology, biochemistry, physics, epidemiology, pharmacology, medical sociology, and others. Applied health sciences endeavor to better understand and improve human health through applications in areas such as health education, biomedical engineering, biotechnology and public health.

Organized interventions to improve health based on the principles and procedures developed through the health sciences are delivered among practitioners trained in medicine, nursing, nutrition, pharmacy, social work, psychology, physical therapy and other health care professions. Clinical practitioners focus mainly on the health of individuals, while public health practitioners consider the overall health of communities and populations. Workplace wellness programs are increasingly adopted by companies for their value in improving the health and well-being of their employees, as are school health services to improve the health and well-being of children.

Role of public health

Public health has been described as "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals."^[16] It is concerned with threats to the overall health of a community based on population health analysis. The population in question can be as small as a handful of people or as large as all the inhabitants of several continents (for instance, in the case of a pandemic). Public health has many sub-fields, but typically includes the interdisciplinary categories of epidemiology, biostatistics and health services. Environmental health, community health, behavioral health, and occupational health, are also important areas of public health.

The focus of public health interventions is to prevent and manage diseases, injuries and other health conditions through surveillance of cases and the promotion of healthy behaviors, communities and environments. Its aim is preventing from happening or re-occurring health problems by implementing educational programs, developing policies, administering services, and conducting research.^[17] In many cases, treating a disease or controlling a pathogen can be vital to preventing it in others, such as during an outbreak. Vaccination programs and distribution of condoms to prevent the spread of communicable diseases are examples of common preventive public health measures.

Public health also takes several actions to limit the health disparities between different areas of the country, continent or world. The great issue is addressing access of individuals and communities to health care, in terms of financial, geographical or sociocultural constraints in access to and use of services. Applications of the public health system include areas of maternal and child health, health services administration, emergency response, and prevention and control of infectious and chronic diseases.

The great positive impact of public health programs is widely acknowledged. Due in part to the policies and actions developed through public health, the 20th century registered a decrease of the mortality rates in infants and children and a continual increase in life expectancy in most parts of the world. For example, it is estimated that the life expectancy has increased for Americans by thirty years since 1900,^[18] and worldwide by six years since 1990.^[19]

Self care strategies

Personal health depends partially on the active, passive, and assisted cues people observe and adopt about their own health. These include personal actions for preventing or minimizing the effects of a disease, usually a chronic condition, through integrative care. They also include personal hygiene practices to prevent infection and illness, such as bathing and washing hands with soap; brushing and flossing teeth; storing, preparing and handling food safely; and many others. The information gleaned from personal observations of daily living - such as about sleep patterns, exercise behavior, nutritional intake, and environmental features - may be used to inform personal decisions and actions (e.g., "I feel tired in the morning so I am going to try sleeping on a different pillow"), as well as clinical decisions and treatment plans (e.g., a patient who notices his or her shoes are tighter than usual may be having exacerbation of left-sided heart failure, and may require diuretic medication to reduce fluid overload).^[20]

Personal health also depends partially on the social structure of a person's life. The maintenance of strong social relationships, volunteering, and other social activities have been linked to positive mental health and even increased longevity. One American study among seniors over age 70 found that frequent volunteering was associated with reduced risk of dying compared with older persons who did not volunteer, regardless of physical health status.^[21] Another study from Singapore reported that volunteering retirees had significantly better cognitive performance scores, fewer depressive symptoms, and better mental well-being and life satisfaction than non-volunteering retirees.^[22]

Prolonged psychological stress may negatively impact health, and has been cited as a factor in cognitive impairment with aging, depressive illness, and expression of disease.^[23] Stress management is the application of methods to either reduce stress or increase tolerance to stress. Relaxation techniques are physical methods used to relieve stress. Psychological methods include cognitive therapy, meditation, and positive thinking which work by reducing response to stress. Improving relevant skills, such as problem solving and time management skills, reduces uncertainty and builds confidence, which also reduces the reaction to stress-causing situations where those skills are applicable. complete health information