Health is the functional and/or metabolic efficiency of an organism, at any moment in time, at both the cellular and global levels. In any organism, health is the ability to efficiently respond to challenges (stressors) and effectively restore and sustain a "state of balance," known as homeostasis. Sickness is merely the absence of health. All organisms, from the simplest to the most complex, reside on a spectrum between 100% health and 0% health.
One widely accepted definition of health is that of the World Health Organization "WHO". It states that "health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity" (WHO, 1946). In more recent years, this statement has been modified to include the ability to lead a "socially and economically productive life." The WHO definition is not without criticism, as some argue that health cannot be defined as a state at all, but must be seen as a process of continuous adjustment to the changing demands of living and of the changing meanings we give to life. The WHO definition is therefore considered by many as an idealistic goal rather than a realistic proposition.
The LaLonde report suggested that there are four general determinants of health which he called "human biology", "environment", "lifestyle", and "healthcare organization" Thus, health is maintained through the science and practice of medicine, but can also be improved by individual effort. Physical fitness, weight loss, healthy eating, stress management training and stopping smoking and other substance abuse are examples of steps to improve one's health. Workplace programs are recognized by an increasingly large number of companies for their value in improving health and well-being of their employees, and increasing morale, loyalty and productivity at work. A company may provide a gym with exercise equipment, start smoking cessation programs, provide nutrition, weight or stress management training. Other programs may include health risk assessments, health screenings and body mass index monitoring.
An increasing measure of the health of populations is height, which is strongly regulated by nutrition and health care, among other standard of living and quality of life matters. The study of human growth, its regulators and its implications is known as auxology.
Wellness is a term sometimes used to describe the psychological state of being healthy, but is most often used in the field of alternative medicine to describe one's state of being.
Physical exercise is the performance of some activity in order to develop or maintain physical fitness and overall health. It is often directed toward also honing athletic ability or skill. Frequent and regular physical exercise is an important component in the prevention of some of the diseases of affluence such as cancer, heart disease, cardiovascular disease, Type 2 diabetes and obesity.
Exercises are generally grouped into three types depending on the overall effect they have on the human body:
- Flexibility exercises such as stretching improve the range of motion of muscles and joints.
- Aerobic exercises such as walking and running focus on increasing cardiovascular endurance.
- Anaerobic exercises such as weight training or sprinting increase short-term muscle strength.
Physical exercise is considered important for maintaining physical fitness including healthy weight; building and maintaining healthy bones, muscles, and joints; promoting physiological well-being; reducing surgical risks; and strengthening the immune system.
Proper nutrition is at least as important to health as exercise. When exercising it becomes even more important to have good diet to ensure the body has the correct ratio of macronutrients whilst providing ample micronutrients, this is to aid the body with the recovery process following strenuous exercise.
Proper rest and recovery is also as important to health as exercise, otherwise the body exists in a permanently injured state and will not improve or adapt adequately to the exercise.
The above two factors can be compromised by psychological compulsions (eating disorders such as exercise bulimia, anorexia, and other bulimias), misinformation, a lack of organization, or a lack of motivation. These all lead to a decreased state of health.
Delayed Onset Muscle Soreness can occur after any kind of exercise, particularly if the body is in an unconditioned state relative to that exercise.
Hygiene is the maintenance of healthy practices. In modern terminology, this is usually regarded as a particular reference to cleanliness. The term Hygiene originates as a reference to Hyieia, who was a daughter of Asclepius and the goddess of health, cleanliness and sanitation. The related term "personal grooming/grooming" means to enhance one's physical appearance or appeal for others, by removing obvious imperfections in one's appearance or improving one's hygiene.
Outward signs of good hygiene include the absence of visible dirt (including dust and stains on clothing) or of bad odor/smells. Since the development of the germ theory of disease, hygiene has come to mean any practice leading to the absence of harmful levels of bacteria.
Good hygiene is an aid to health, beauty, comfort, and social interactions. It directly aids in disease prevention and/or disease isolation. (That is, good hygiene will help keep one healthy and thus avoid illness. If one is ill, good hygiene can reduce one's contagiousness to others.)
Washing (with water) is the most common example of hygienic behavior. Washing is often done with soap or detergent which helps to remove oils and to break up dirt particles so they may be washed away.
Hygienic practices—such as frequent hand washing or the use of boiled (and thus sterilized) water in surgery/medical operations—have a profound impact on reducing the spread of disease. This is because they kill or remove disease-causing microbes (germs) in the immediate surroundings. For instance, washing one's hands after using the toilet and before handling food reduces the chance of spreading E. coli bacteria and Hepatitis A, both of which are spread from fecal contamination of food.
Adequate hygiene requires an adequate and convenient supply of clean water. In much of the developing world maintaining an acceptable level of cleanliness is difficult or impossible for much of the population due to lack of adequate water supply and sanitation. This results in the rapid spread and extent of diseases such as trachoma which are rare in the developed world.
Nutrition is a science which studies the relationship between diet and states of health and disease. Dieticians are Health professionals who are specialized in this area of expertise. They are also the only highly trained health professionals able to provide safe, evidence-based and accurate dietary advice and interventions.
Between the extremes of optimal health and death from starvation or malnutrition, there is an array of disease states that can be caused or alleviated by changes in diet. Deficiencies, excesses and imbalances in diet can produce negative impacts on health, which may lead to diseases such as scurvy, obesity or osteoporosis, as well as psychological and behavioral problems. Moreover, excessive ingestion of elements that have no apparent role in health, (e.g. lead, mercury, PCBs, dioxins), may incur toxic and potentially lethal effects, depending on the dose. The science of nutrition attempts to understand how and why specific dietary aspects influence health.
Mental health is a concept that refers to a human individual's emotional and psychological well-being. Merriam-Webster defines mental health as "A state of emotional and psychological well-being in which an individual is able to use his or her cognitive and emotional capabilities, function in society, and meet the ordinary demands of everyday life."
According to the World Health Organization (WHO), there is no one "official" definition of mental health. Cultural differences, subjective assessments, and competing professional theories all affect how "mental health" is defined. In general, most experts agree that "mental health" and "mental illness" are not opposites. In other words, the absence of a recognized mental disorder is not necessarily an indicator of mental health.
One way to think about mental health is by looking at how effectively and successfully a person functions. Feeling capable and competent; being able to handle normal levels of stress, maintain satisfying relationships, and lead an independent life; and being able to "bounce back," or recover from difficult situations, are all signs of mental health.