Any factor, whether event, characteristic or other definable entity, that brings about change in a health condition or other defined characteristic.
The dependence that most concerns modern society is one in which individuals become dependent on or addicted to certain substances such as alcohol, drugs, tobacco (nicotine), caffeine and solvents. This is often called substance abuse. Some people become addicted to certain foods or activities: examples of the latter include gambling, computer games and use of the Internet.
The 28th report of the World Health Organisation Expert Committee on Drug Dependence in 1993 de?ned drug dependence as: ‘A cluster of physiological, behavioural and cognitive phenomena of variable intensity, in which the use of a psychoactive drug (or drugs) takes on a high priority. The necessary descriptive characteristics are preoccupation with a desire to obtain and take the drug and persistent drug-seeking behaviour. Psychological dependence occurs when the substance abuser craves the drug’s desirable effects. Physical dependence occurs when the user has to continue taking the drug to avoid distressing withdrawal or abstinence symptoms. Thus, determinants and the problematic consequences of drug dependence may be biological, psychological or social and usually interact.’
Di?erent drugs cause di?erent rates of dependence: TOBACCO is the most common substance of addiction; HEROIN and COCAINE cause high rates of addiction; whereas ALCOHOL is much lower, and CANNABIS lower again. Smoking in the western world reached a peak after World War II with almost 80 per cent of the male population smoking. The reports on the link between smoking and cancer in the early 1960s resulted in a decline that has continued so that only around a quarter of the adult populations of the UK and USA smokes. Globally, tobacco consumption continues to grow, particularly in the developing world with multinational tobacco companies marketing their products aggressively.
Accurate ?gures for illegal drug-taking are hard to obtain, but probably approximately 4 per cent of the population is dependent on alcohol and 2 per cent on other drugs, both legal and illegal, at any one time in western countries.
How does dependence occur? More than 40 distinct theories or models of drug misuse have been put forward. One is that the individual consumes drugs to cope with personal problems or diffculties in relations with others. The other main model emphasises environmental in?uences such as drug availability, environmental pressures to consume drugs, and sociocultural in?uences such as peer pressure.
By contrast to these models of why people misuse drugs, models of compulsive drug use – where individuals have a compulsive addiction
– have been amenable to testing in the laboratory. Studies at cellular and nerve-receptor levels are attempting to identify mechanisms of tolerance and dependence for several substances. Classical behaviour theory is a key model for understanding drug dependence. This and current laboratory studies are being used to explain the reinforcing nature of dependent substances and are helping to provide an explanatory framework for dependence. Drug consumption is a learned form of behaviour. Numerous investigators have used conditioning theories to study why people misuse drugs. Laboratory studies are now locating the ‘reward pathways’ in the brain for opiates and stimulants where positive reinforcing mechanisms involve particular sectors of the brain. There is a consensus among experts in addiction that addictive behaviour is amenable to e?ective treatment, and that the extent to which an addict complies with treatment makes it possible to predict a positive outcome. But there is a long way to go before the mechanisms of drug addiction are properly understood or ways of treating it generally agreed.
Effects of drugs Cannabis, derived from the plant Cannabis sativa, is a widely used recreational drug. Its two main forms are marijuana, which comes from the dried leaves, and hashish which comes from the resin. Cannabis may be used in food and drink but is usually smoked in cigarettes to induce relaxation and a feeling of well-being. Heavy use can cause apathy and vagueness and may even cause psychosis. Whether or not cannabis leads people to using harder drugs is arguable, and a national debate is underway on whether its use should be legalised for medicinal use. Cannabis may alleviate the symptoms of some disorders – for example, MULTIPLE SCLEROSIS (MS) – and there are calls to allow the substance to be classi?ed as a prescribable drug.
About one in ten of Britain’s teenagers misuses volatile substances such as toluene at some time, but only about one in 40 does so regularly. These substances are given o? by certain glues, solvents, varnishes, and liquid fuels, all of which can be bought cheaply in shops, although their sale to children under 16 is illegal. They are often inhaled from plastic bags held over the nose and mouth. Central-nervous-system excitation, with euphoria and disinhibition, is followed by depression and lethargy. Unpleasant effects include facial rash, nausea and vomiting, tremor, dizziness, and clumsiness. Death from COMA and acute cardiac toxicity is a serious risk. Chronic heavy use can cause peripheral neuropathy and irreversible cerebellar damage. (See SOLVENT ABUSE (MISUSE).)
The hallucinogenic or psychedelic drugs include LYSERGIC ACID DIETHYLAMIDE (LSD) or acid, magic mushrooms, ecstasy (MDMA), and phencyclidine (PCP or ‘angel’ dust, mainly used in the USA). These drugs have no medicinal uses. Taken by mouth, they produce vivid ‘trips’, with heightened emotions and perceptions and sometimes with hallucinations. They are not physically addictive but can cause nightmarish bad trips during use and ?ashbacks (vivid reruns of trips) after use, and can probably trigger psychosis and even death, especially if drugs are mixed or taken with alcohol.
Stimulant drugs such as amphetamine and cocaine act like adrenaline and speed up the central nervous system, making the user feel con?dent, energetic, and powerful for several hours. They can also cause severe insomnia, anxiety, paranoia, psychosis, and even sudden death due to convulsions or tachycardia. Depression may occur on withdrawal of these drugs, and in some users this is su?ciently deterrent to cause psychological dependence. Amphetamine (‘speed’) is mainly synthesised illegally and may be eaten, sni?ed, or injected. Related drugs, such as dexamphetamine sulphate (Dexedrine), are prescribed pills that enter the black market. ECSTASY is another amphetamine derivative that has become a popular recreational drug; it may have fatal allergic effects. Cocaine and related drugs are used in medicine as local anaesthetics. Illegal supplies of cocaine (‘snow’ or ‘ice’) and its derivative, ‘crack’, come mainly from South America, where they are made from the plant Erythroxylon coca. Cocaine is usually sni?ed (‘snorted’) or rubbed into the gums; crack is burnt and inhaled.
Opiate drugs are derived from the opium poppy, Papaver somniferum. They are described as narcotic because they induce sleep. Their main medical use is as potent oral or injectable analgesics such as MORPHINE, DIAMORPHINE, PETHIDINE HYDROCHLORIDE, and CODEINE. The commonest illegal opiate is heroin, a powdered form of diamorphine that may be smoked, sni?ed, or injected to induce euphoria and drowsiness. Regular opiate misuse leads to tolerance (the need to take ever larger doses to achieve the same e?ect) and marked dependence. A less addictive oral opiate, METHADONE HYDROCHLORIDE, can be prescribed as a substitute that is easier to withdraw.
Some 75,000–150,000 Britons now misuse opiates and other drugs intravenously, and pose a huge public-health problem because injections with shared dirty needles can carry the blood-borne viruses that cause AIDS/HIV and HEPATITIS B. Many clinics now operate schemes to exchange old needles for clean ones, free of charge. Many addicts are often socially disruptive.
For help and advice see APPENDIX 2: ADDRESSES: SOURCES OF INFORMATION, ADVICE, SUPPORT AND SELF-HELP – National Dugs Helpline.
(See ALCOHOL and TOBACCO for detailed entries on those subjects.)... dependence
Insulin-dependent and non-insulindependent diabetes have a varied pathological pattern and are caused by the interaction of several genetic and environmental factors.
Insulin-dependent diabetes mellitus (IDDM) (juvenile-onset diabetes, type 1 diabetes) describes subjects with a severe de?ciency or absence of insulin production. Insulin therapy is essential to prevent KETOSIS – a disturbance of the body’s acid/base balance and an accumulation of ketones in the tissues. The onset is most commonly during childhood, but can occur at any age. Symptoms are acute and weight loss is common.
Non-insulin-dependent diabetes mellitus (NIDDM) (maturity-onset diabetes, type 2 diabetes) may be further sub-divided into obese and non-obese groups. This type usually occurs after the age of 40 years with an insidious onset. Subjects are often overweight and weight loss is uncommon. Ketosis rarely develops. Insulin production is reduced but not absent.
A new hormone has been identi?ed linking obesity to type 2 diabetes. Called resistin – because of its resistance to insulin – it was ?rst found in mice but has since been identi?ed in humans. Researchers in the United States believe that the hormone may, in part, explain how obesity predisposes people to diabetes. Their hypothesis is that a protein in the body’s fat cells triggers insulin resistance around the body. Other research suggests that type 2 diabetes may now be occurring in obese children; this could indicate that children should be eating a more-balanced diet and taking more exercise.
Diabetes associated with other conditions (a) Due to pancreatic disease – for example, chronic pancreatitis (see PANCREAS, DISORDERS OF); (b) secondary to drugs – for example, GLUCOCORTICOIDS (see PANCREAS, DISORDERS OF); (c) excess hormone production
– for example, growth hormone (ACROMEGALY); (d) insulin receptor abnormalities; (e) genetic syndromes (see GENETIC DISORDERS).
Gestational diabetes Diabetes occurring in pregnancy and resolving afterwards.
Aetiology Insulin-dependent diabetes occurs as a result of autoimmune destruction of beta cells within the PANCREAS. Genetic in?uences are important and individuals with certain HLA tissue types (HLA DR3 and HLA DR4) are more at risk; however, the risks associated with the HLA genes are small. If one parent has IDDM, the risk of a child developing IDDM by the age of 25 years is 1·5–2·5 per cent, and the risk of a sibling of an IDDM subject developing diabetes is about 3 per cent.
Non-insulin-dependent diabetes has no HLA association, but the genetic in?uences are much stronger. The risks of developing diabetes vary with di?erent races. Obesity, decreased exercise and ageing increase the risks of disease development. The risk of a sibling of a NIDDM subject developing NIDDM up to the age of 80 years is 30–40 per cent.
Diet Many NIDDM diabetics may be treated with diet alone. For those subjects who are overweight, weight loss is important, although often unsuccessful. A diet high in complex carbohydrate, high in ?bre, low in fat and aiming towards ideal body weight is prescribed. Subjects taking insulin need to eat at regular intervals in relation to their insulin regime and missing meals may result in hypoglycaemia, a lowering of the amount of glucose in the blood, which if untreated can be fatal (see below).
Oral hypoglycaemics are used in the treatment of non-insulin-dependent diabetes in addition to diet, when diet alone fails to control blood-sugar levels. (a) SULPHONYLUREAS act mainly by increasing the production of insulin;
(b) BIGUANIDES, of which only metformin is available, may be used alone or in addition to sulphonylureas. Metformin’s main actions are to lower the production of glucose by the liver and improve its uptake in the peripheral tissues.
Complications The risks of complications increase with duration of disease.
Diabetic hypoglycaemia occurs when amounts of glucose in the blood become low. This may occur in subjects taking sulphonylureas or insulin. Symptoms usually develop when the glucose concentration falls below 2·5 mmol/l. They may, however, occur at higher concentrations in subjects with persistent hyperglycaemia – an excess of glucose – and at lower levels in subjects with persistent hypo-glycaemia. Symptoms include confusion, hunger and sweating, with coma developing if blood-sugar concentrations remain low. Re?ned sugar followed by complex carbohydrate will return the glucose concentration to normal. If the subject is unable to swallow, glucagon may be given intramuscularly or glucose intravenously, followed by oral carbohydrate, once the subject is able to swallow.
Although it has been shown that careful control of the patient’s metabolism prevents late complications in the small blood vessels, the risk of hypoglycaemia is increased and patients need to be well motivated to keep to their dietary and treatment regime. This regime is also very expensive. All risk factors for the patient’s cardiovascular system – not simply controlling hyperglycaemia – may need to be reduced if late complications to the cardiovascular system are to be avoided.
Diabetes is one of the world’s most serious health problems. Recent projections suggest that the disorder will affect nearly 240 million individuals worldwide by 2010 – double its prevalence in 1994. The incidence of insulin-dependent diabetes is rising in young children; they will be liable to develop late complications.
Although there are complications associated with diabetes, many subjects live normal lives and survive to an old age. People with diabetes or their relatives can obtain advice from Diabetes UK (www.diabetes.org.uk).
Increased risks are present of (a) heart disease, (b) peripheral vascular disease, and (c) cerebrovascular disease.
Diabetic eye disease (a) retinopathy, (b) cataract. Regular examination of the fundus enables any abnormalities developing to be detected and treatment given when appropriate to preserve eyesight.
Nephropathy Subjects with diabetes may develop kidney damage which can result in renal failure.
Neuropathy (a) Symmetrical sensory polyneuropathy; damage to the sensory nerves that commonly presents with tingling, numbness of pain in the feet or hands. (b) Asymmetrical motor diabetic neuropathy, presenting as progressive weakness and wasting of the proximal muscles of legs. (c) Mononeuropathy; individual motor or sensory nerves may be affected. (d) Autonomic neuropathy, which affects the autonomic nervous system, has many presentations including IMPOTENCE, diarrhoea or constipation and postural HYPOTENSION.
Skin lesions There are several skin disorders associated with diabetes, including: (a) necrobiosis lipoidica diabeticorum, characterised by one or more yellow atrophic lesions on the legs;
(b) ulcers, which most commonly occur on the feet due to peripheral vascular disease, neuropathy and infection. Foot care is very important.
Diabetic ketoacidosis occurs when there is insu?cient insulin present to prevent KETONE production. This may occur before the diagnosis of IDDM or when insu?cient insulin is being given. The presence of large amounts of ketones in the urine indicates excess ketone production and treatment should be sought immediately. Coma and death may result if the condition is left untreated.
Symptoms Thirst, POLYURIA, GLYCOSURIA, weight loss despite eating, and recurrent infections (e.g. BALANITIS and infections of the VULVA) are the main symptoms.
However, subjects with non-insulindependent diabetes may have the disease for several years without symptoms, and diagnosis is often made incidentally or when presenting with a complication of the disease.
Treatment of diabetes aims to prevent symptoms, restore carbohydrate metabolism to as near normal as possible, and to minimise complications. Concentration of glucose, fructosamine and glycated haemoglobin in the blood are used to give an indication of blood-glucose control.
Insulin-dependent diabetes requires insulin for treatment. Non-insulin-dependent diabetes may be treated with diet, oral HYPOGLYCAEMIC AGENTS or insulin.
Insulin All insulin is injected – mainly by syringe but sometimes by insulin pump – because it is inactivated by gastrointestinal enzymes. There are three main types of insulin preparation: (a) short action (approximately six hours), with rapid onset; (b) intermediate action (approximately 12 hours); (c) long action, with slow onset and lasting for up to 36 hours. Human, porcine and bovine preparations are available. Much of the insulin now used is prepared by genetic engineering techniques from micro-organisms. There are many regimens of insulin treatment involving di?erent combinations of insulin; regimens vary depending on the requirements of the patients, most of whom administer the insulin themselves. Carbohydrate intake, energy expenditure and the presence of infection are important determinants of insulin requirements on a day-to-day basis.
A new treatment for diabetes, pioneered in Canada and entering its preliminary clinical trials in the UK, is the transplantation of islet cells of Langerhans from a healthy person into a patient with the disorder. If the transplantation is successful, the transplanted cells start producing insulin, thus reducing or eliminating the requirement for regular insulin injections. If successful the trials would be a signi?cant advance in the treatment of diabetes.
Scientists in Israel have developed a drug, Dia Pep 277, which stops the body’s immune system from destroying pancratic ? cells as happens in insulin-dependent diabetes. The drug, given by injection, o?ers the possibility of preventing type 1 diabetes in healthy people at genetic risk of developing the disorder, and of checking its progression in affected individuals whose ? cells are already perishing. Trials of the drug are in progress.... diabetes mellitus
Health has driven much of environmental policy since the work of Edwin Chadwick in the early 1840s. The ?rst British public-health act was introduced in 1848 to improve housing and sanitation with subsequent provision of puri?ed water, clean milk, food hygiene regulations, vaccinations and antibiotics. In the 21st century there are now many additional environmental factors that must be monitored, researched and controlled if risks to human health are to be well managed and the impact on human morbidity and mortality reduced.
Environmental impacts on health include:
noise
air pollution
water pollution
dust •odours
contaminated ground
loss of amenities
vermin
vibration
animal diseases
Environmental risk factors Many of the major determinants of health, disease and death are environmental risk factors. Some are natural hazards; others are generated by human activities. They may be directly harmful, as in the examples of exposure to toxic chemicals at work, pesticides, or air pollution from road transport, or to radon gas penetrating domestic properties. Environmental factors may also alter people’s susceptibility to disease: for example, the availability of su?cient food. In addition, they may operate by making unhealthy choices more likely, such as the availability and a?ord-ability of junk foods, alcohol, illegal drugs or tobacco.
Populations at risk Children are among the populations most sensitive to environmental health hazards. Their routine exposure to toxic chemicals in homes and communities can put their health at risk. Central to the ability to protect communities and families is the right of people to know about toxic substances. For many, the only source of environmental information is media reporting, which often leaves the public confused and frustrated. To bene?t from public access to information, increasingly via the Internet, people need basic environmental and health information, resources for interpreting, understanding and evaluating health risks, and familiarity with strategies for prevention or reduction of risk.
Risk assessment Environmental health experts rely on the principles of environmental toxicology and risk assessment to evaluate the environment and the potential effects on individual and community health. Key actions include:
identifying sources and routes of environmental exposure and recommending methods of reducing environmental health risks, such as exposure to heavy metals, solvents, pesticides, dioxins, etc.
assessing the risks of exposure-related health hazards.
alerting health professionals, the public, and the media to the levels of risk for particular potential hazards and the reasons for interventions.
ensuring that doctors and scientists explain the results of environmental monitoring studies – for example, the results of water ?uoridation in the UK to improve dental health.
National policies In the United Kingdom in 1996, an important step in linking environment and health was taken by a government-initiated joint consultation by the Departments of Health and Environment about adding ‘environment’ as a key area within the Health of the Nation strategy. The ?rst UK Minister of State for Public Health was appointed in 1997 with responsibilities for health promotion and public-health issues, both generally and within the NHS. These responsibilities include the implementation of the Health of the Nation strategy and its successor, Our Healthy Nation. The aim is to raise the priority given to human health throughout government departments, and to make health and environmental impact assessment a routine part of the making, implementing and assessing the impact of policies.
Global environmental risks The scope of many environmental threats to human health are international and cannot be regulated e?ectively on a local, regional or even national basis. One example is the Chernobyl nuclear reactor accident, which led to a major release of radiation, the effects of which were felt in many countries. Some international action has already been taken to tackle global environmental problems, but governments should routinely measure the overall impacts of development on people and their environments and link with industry to reduce damage to the environment. For instance, the effects of global warming and pollution on health should be assessed within an ecological framework if communities are to respond e?ectively to potential new global threats to the environment.... environment and health
Central to an understanding of public health is recognition that public-health practitioners are concerned not just with individuals, but also with whole populations – and that improving health care plays only a part of public-health improvement. The health of populations (public health) is also dependent on many factors such as the social, economic and physical environment in which the people live and the nutrition and health care available to them.
For thousands of years, a fundamental feature of civilisations has been to seek to improve the health of the population and protect it from disease. This has led to the development of legal frameworks which di?er widely from country to country, depending on their social and political development. All are concerned to stop the spread of infectious diseases, and to maintain the safety of urban food and water supplies and waste disposal. Most are also associated with housing standards, some form of poverty relief, and basic health care. Some trading standards are often covered, at least in relation to the sale and distribution of poisons and drugs, and to controls on industrial and transport safety – for example, in relation to drinking and driving and car design. Although these varied functions protect the public health and were often originally developed to improve it, most are managerially and professionally separated from today’s public-health departments. So public-health professionals in the NHS, armed with evidence of the cause of a disease problem, must frequently act as advocates for health across many agencies where they play no formal management part. They must also seek to build alliances and add a health perspective to the policies of other services wherever possible.
Epidemiology is the principal diagnostic method of public health. It is de?ned as the study of the distribution and determinants of health-related states in speci?ed populations, and the application of this study to the control of health problems. Public-health practitioners also draw on many other skills, such as those of statisticians, sociologists, anthropologists, economists and policy analysts in identifying and trying to resolve the health problems of the societies they serve. Treatments proposed are likely to extend well beyond the clinic or hospital and may include recommendations for measures to resolve poverty, improve sanitation or housing, control pollution, change lifestyles such as smoking, improve nutrition, or change health services. At times of acute EPIDEMIC, public-health doctors have considerable legal powers granted to enable them to prevent infection from spreading. At other times their work may be more concerned with monitoring, reporting, planning and managing services, and advocating policy changes to politicians so that health is promoted.
The term ‘the public health’ can relate to the state of health of the population, and be represented by measures such as MORTALITY indices
(e.g. perinatal or infant mortality and standardised mortality rates), life expectancy, or measures of MORBIDITY (illness). These can be compared across areas and even countries. Sometimes people refer to a pubic health-care system; this is a publicly funded service, the primary aim of which is to improve health by the use of population-based measures. They may include or be separate from private health-care services for which individuals pay. The structure of these systems varies from country to country, re?ecting di?erent social composition and political priorities. There are, however, some general elements that can be identi?ed:
Surveillance The collection, collation and analysis of data to provide useful information about the distribution and causes of health and disease and related factors in populations. These activities form the basis of epidemiology, which is the diagnostic backbone of public-health practice.
Intervention The design, advocacy and implementation of policies to improve health. This may be through the provison of PREVENTIVE MEDICINE, environmental measures, in?uencing the behaviour of individuals, or the provision of appropriate services to limit disability and handicap. It will lead to advocacy for health, promoting change in many areas of policy including, for example, taxation and improved housing and employment opportunities.
Evaluation Assessment of the ?rst two steps to assess their impact in terms of e?ectiveness, e?ciency, acceptability, accessibility, value for money or other indicators of quality. This enables the programme to be reviewed and changed as necessary.
The practice of public health The situation in the United Kingdom will be described as, even though systems vary, it will give a general impression of the type of work covered. HISTORY Initially, public-health practice related to food, the urban environment and the control of infectious diseases. Early examples include rules in the Bible about avoiding certain foods. These were probably based on practical experience, had gradually been adopted as sensible behaviour, become part of culture and ?nally been incorporated into religious laws. Other examples are the regulations about quarantine for PLAGUE and LEPROSY in the Middle Ages, vaccination against SMALLPOX introduced by William Jenner, and Lind’s use of citrus fruits to prevent SCURVY at sea in the 18th century.
It was during the 19th century, in response to the health problems arising from the rapid growth of urban life, that the foundations of a public-health system were created. The ‘sanitary’ concept was fundamental to these developments. This suggested that overcrowding in insanitary conditions was the cause of most disease epidemics and that improved sanitation measures such as sewerage and clean water supplies would prevent them. Action to introduce such measures were often initiated only after epidemics spread out of the slums and into wealthier and more powerful families. Other problems such as the stench of the River Thames outside the Houses of Parliament also led to a demand for e?ective sanitary control measures. Successive public-health laws were passed by Parliament, initially about sanitation and housing, and then, as scienti?c knowledge grew, about bacterial infections.
In the middle of the 19th century the ?rst medical o?cers of health were appointed with responsibility to report regularly and advise local government about the measures needed to control disease and improve health. Their scope and responsibility widened as society changed and took on a wider welfare role. After more than a century they changed as part of the reforms of the NHS and local government in the 1960s and became more narrowly focused within the health-care system and its management. Increased recognition of the multifactorial causes, costs and limitations of treatment of conditions such as cancer and heart disease, and the emergence of new problems such as AIDS/HIV and BOVINE SPONGIFORM ENCEPHALOPATHY (BSE) have again showed the importance of prevention and a broader approach to health. With it has come recognition that, while disease may be the justi?cation for action, a narrow diseasetreatment-based approach is not always the most e?ective or economic solution. The role of the director of public health (the successor to the medical o?cer of health) is again being expanded, and in 1997 – for the ?rst time in the UK – a government Minister for Public Health was appointed. This reffects not only a greater priority for public health, but also a concern that the health effects of policy should be considered across all parts of government.
(See also ENVIRONMENT AND HEALTH.)... public health
form. In the absence of these hormones, a female reproductive tract develops. At puberty, another surge of hormones produces secondary sexual characteristics.
Chromosomal abnormalities or hormonal defects can lead to ambiguous sex (see genitalia, ambiguous), although true hermaphroditism is rare.... sex determination
Heredity is an important determinant of life expectancy, but physical degeneration may be accelerated by factors such as smoking, excessive alcohol intake, poor diet, and insufficient exercise.... aging
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