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. 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.
The national system of health insurance was instituted in 1945, just after the end of the Second World War. It was a compromise between Gaullist and Communist representatives in the French parliament. The Conservative Gaullists were opposed to a state-run healthcare system, while the Communists were supportive of a complete nationalisation of health care along a British Beveridge model.
Insurance companies are not allowed to have co-payments, caps, or deductibles, or to deny coverage to any person applying for a policy, or to charge anything other than their nationally set and published standard premiums. Therefore, every person buying insurance will pay the same price as everyone else buying the same policy, and every person will get at least the minimum level of coverage.
Comprehensive health insurance pays a percentage of the cost of hospital and physician charges after a deductible (usually applies to hospital charges) or a co-pay (usually applies to physician charges, but may apply to some hospital services) is met by the insured. These plans are generally expensive because of the high potential benefit payout — $1,000,000 to $5,000,000 is common — and because of the vast array of covered benefits.
When a clearer distinction is intended, healthy is used to describe the state of the object, and healthful describes its ability to impart health to the recipient. Vegetables in good condition are both healthy (i.e., not rotten or diseased) and healthful (i.e., they improve the eaters' health, compared to eating junk food). By contrast, a poisonous plant can be healthy, but it is not healthful to eat it.
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. For example, genetics may play a role in the manner in which people cope with stress, either mental, emotional or physical. For example, obesity is a significant problem in the United States that contributes to bad mental health and causes stress in the lives of great numbers of people[32]. (One difficulty is the issue raised by the debate over the relative strengths of genetics and other factors; interactions between genetics and environment may be of particular importance.)

The UK's National Health Service (NHS) is a publicly funded healthcare system that provides coverage to everyone normally resident in the UK. It is not strictly an insurance system because (a) there are no premiums collected, (b) costs are not charged at the patient level and (c) costs are not pre-paid from a pool. However, it does achieve the main aim of insurance which is to spread financial risk arising from ill-health. The costs of running the NHS (est. £104 billion in 2007-8)[48] are met directly from general taxation. The NHS provides the majority of health care in the UK, including primary care, in-patient care, long-term health care, ophthalmology, and dentistry.
Health, as defined by the World Health Organization (WHO), is "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity."[1][2] This definition has been subject to controversy, as it may have limited value for implementation.[3][4][5] Health may be defined as the ability to adapt and manage physical, mental and social challenges throughout life.[6]