Healthy diet

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Healthy_diet 

 

Leafy green, cruciferous, and other vegetables may contribute to a healthy diet

A healthy diet is a diet that helps maintain or improve overall health. A healthy diet provides the body with essential nutrition: fluid, macronutrients, micronutrients, and adequate food energy.

A healthy diet may contain fruits, vegetables, and whole grains, and may include little to no processed food or sweetened beverages. The requirements for a healthy diet can be met from a variety of plant-based and animal-based foods, although a non-plant source of vitamin B12 is needed for those following a vegan diet. Various nutrition guides are published by medical and governmental institutions to educate individuals on what they should be eating to be healthy. Nutrition facts labels are also mandatory in some countries to allow consumers to choose between foods based on the components relevant to health.

Recommendations

World Health Organization

The World Health Organization (WHO) makes the following five recommendations with respect to both populations and individuals:

1. Maintain a healthy weight by eating roughly the same number of calories that your body is using.
2. Limit intake of fats. Not more than 30% of the total calories should come from fats. Prefer unsaturated fats to saturated fats. Avoid trans fats.
3. Eat at least 400 grams of fruits and vegetables per day (potatoes, sweet potatoes, cassava and other starchy roots do not count). A healthy diet also contains legumes (e.g. lentils, beans), whole grains and nuts.
4. Limit the intake of simple sugars to less than 10% of calorie (below 5% of calories or 25 grams may be even better).
5. Limit salt / sodium from all sources and ensure that salt is iodized. Less than 5 grams of salt per day can reduce the risk of cardiovascular disease.

The WHO has stated that insufficient vegetables and fruit is the cause of 2.8% of deaths worldwide.

Other WHO recommendations include:

• ensuring that the foods chosen have sufficient vitamins and certain minerals;
• avoiding directly poisonous (e.g. heavy metals) and carcinogenic (e.g. benzene) substances;
• avoiding foods contaminated by human pathogens (e.g. E. coli, tapeworm eggs);
• and replacing saturated fats with polyunsaturated fats in the diet, which can reduce the risk of coronary artery disease and diabetes.

United States Department of Agriculture

The Dietary Guidelines for Americans by the United States Department of Agriculture (USDA) recommends three healthy patterns of diet, summarized in the table below, for a 2000 kcal diet.

The guidelines emphasize both health and environmental sustainability and a flexible approach. The committee that drafted it wrote: "The major findings regarding sustainable diets were that a diet higher in plant-based foods, such as vegetables, fruits, whole grains, legumes, nuts, and seeds, and lower in calories and animal-based foods is more health promoting and is associated with less environmental impact than is the current U.S. diet. This pattern of eating can be achieved through a variety of dietary patterns, including the “Healthy U.S.-style Pattern”, the “Healthy Vegetarian Pattern" and the "Healthy Mediterranean-style Pattern". Food group amounts are per day, unless noted per week.

The three healthy patterns

Food group/subgroup (units)	U.S. style	Vegetarian	Med-style
Fruits (cup eq)	2	2	2.5
Vegetables (cup eq)	2.5	2.5	2.5
Dark green	1.5/wk	1.5/wk	1.5/wk
Red/orange	5.5/wk	5.5/wk	5.5/wk
Starchy	5/wk	5/wk	5/wk
Legumes	1.5/wk	3/wk	1.5/wk
Others	4/wk	4/wk	4/wk
Grains (oz eq)	6	6.5	6
Whole	3	3.5	3
Refined	3	3	3
Dairy (cup eq)	3	3	2
Protein Foods (oz eq)	5.5	3.5	6.5
Meat (red and processed)	12.5/wk	--	12.5/wk
Poultry	10.5/wk	--	10.5/wk
Seafood	8/wk	--	15/wk
Eggs	3/wk	3/wk	3/wk
Nuts/seeds	4/wk	7/wk	4/wk
Processed Soy (including tofu)	0.5/wk	8/wk	0.5/wk
Oils (grams)	27	27	27
Solid fats limit (grams)	18	21	17
Added sugars limit (grams)	30	36	29

American Heart Association / World Cancer Research Fund / American Institute for Cancer Research

The American Heart Association, World Cancer Research Fund, and American Institute for Cancer Research recommend a diet that consists mostly of unprocessed plant foods, with emphasis on a wide range of whole grains, legumes, and non-starchy vegetables and fruits. This healthy diet includes a wide range of non-starchy vegetables and fruits which provide different colors including red, green, yellow, white, purple, and orange. The recommendations note that tomato cooked with oil, allium vegetables like garlic, and cruciferous vegetables like cauliflower, provide some protection against cancer. This healthy diet is low in energy density, which may protect against weight gain and associated diseases. Finally, limiting consumption of sugary drinks, limiting energy rich foods, including “fast foods” and red meat, and avoiding processed meats improves health and longevity. Overall, researchers and medical policy conclude that this healthy diet can reduce the risk of chronic disease and cancer.

It is recommended that children consume less than 25 grams of added sugar (100 calories) per day. Other recommendations include no extra sugars in those under 2 years old and less than one soft drink per week. As of 2017, decreasing total fat is no longer recommended, but instead, the recommendation to lower risk of cardiovascular disease is to increase consumption of monounsaturated fats and polyunsaturated fats, while decreasing consumption of saturated fats.

Harvard School of Public Health

The Nutrition Source of Harvard School of Public Health makes the following 10 recommendations for a healthy diet:

• Choose good carbohydrates: whole grains (the less processed the better), vegetables, fruits and beans. Avoid white bread, white rice, and the like as well as pastries, sugared sodas, and other highly processed food.
• Pay attention to the protein package: good choices include fish, poultry, nuts, and beans. Try to avoid red meat.
• Choose foods containing healthy fats. Plant oils, nuts, and fish are the best choices. Limit consumption of saturated fats, and avoid foods with trans fat.
• Choose a fiber-filled diet which includes whole grains, vegetables, and fruits.
• Eat more vegetables and fruits—the more colorful and varied, the better.
• Include adequate amounts of calcium in the diet; however, milk is not the best or only source. Good sources of calcium are collards, bok choy, fortified soy milk, baked beans, and supplements containing calcium and vitamin D.
• Prefer water over other beverages. Avoid sugary drinks, and limit intake of juices and milk. Coffee, tea, artificially-sweetened drinks, 100% fruit juices, low-fat milk and alcohol can fit into a healthy diet but are best consumed in moderation. Sports drinks are recommended only for people who exercise more than an hour at a stretch to replace substances lost in sweat.
• Limit salt intake. Choose more fresh foods, instead of processed ones.
• Drink alcohol in moderation. Doing so has health benefits, but is not recommended for everyone.
• Consider intake of daily multivitamin and extra vitamin D, as these have potential health benefits.

Other than nutrition, the guide recommends frequent physical exercise and maintaining a healthy body weight.

Others

David L. Katz, who reviewed the most prevalent popular diets in 2014, noted:

The weight of evidence strongly supports a theme of healthful eating while allowing for variations on that theme. A diet of minimally processed foods close to nature, predominantly plants, is decisively associated with health promotion and disease prevention and is consistent with the salient components of seemingly distinct dietary approaches. Efforts to improve public health through diet are forestalled not for want of knowledge about the optimal feeding of Homo sapiens but for distractions associated with exaggerated claims, and our failure to convert what we reliably know into what we routinely do. Knowledge in this case is not, as of yet, power; would that it were so.

Marion Nestle expresses the mainstream view among scientists who study nutrition:

The basic principles of good diets are so simple that I can summarize them in just ten words: eat less, move more, eat lots of fruits and vegetables. For additional clarification, a five-word modifier helps: go easy on junk foods. Follow these precepts and you will go a long way toward preventing the major diseases of our overfed society—coronary heart disease, certain cancers, diabetes, stroke, osteoporosis, and a host of others.... These precepts constitute the bottom line of what seem to be the far more complicated dietary recommendations of many health organizations and national and international governments—the forty-one “key recommendations” of the 2005 Dietary Guidelines, for example. ... Although you may feel as though advice about nutrition is constantly changing, the basic ideas behind my four precepts have not changed in half a century. And they leave plenty of room for enjoying the pleasures of food.

Historically, a healthy diet was defined as a diet comprising more than 55% of carbohydrates, less than 30% of fat and about 15% of proteins. This view is currently shifting towards a more comprehensive framing of dietary needs as a global need of various nutrients with complex interactions, instead of per nutrient type needs.

Specific conditions

In addition to dietary recommendations for the general population, there are many specific diets that have primarily been developed to promote better health in specific population groups, such as people with high blood pressure (such as low sodium diets or the more specific DASH diet), or people who are overweight or obese (weight control diets). Some of them may have more or less evidence for beneficial effects in normal people as well.

Hypertension

A low sodium diet is beneficial for people with high blood pressure. A Cochrane review published in 2008 concluded that a long-term (more than four weeks) low sodium diet usefully lowers blood pressure, both in people with hypertension (high blood pressure) and in those with normal blood pressure.

The DASH diet (Dietary Approaches to Stop Hypertension) is a diet promoted by the National Heart, Lung, and Blood Institute (part of the NIH, a United States government organization) to control hypertension. A major feature of the plan is limiting intake of sodium, and the diet also generally encourages the consumption of nuts, whole grains, fish, poultry, fruits, and vegetables while lowering the consumption of red meats, sweets, and sugar. It is also "rich in potassium, magnesium, and calcium, as well as protein".

The Mediterranean diet, which includes limiting consumption of red meat and using olive oil in cooking, has also been shown to improve cardiovascular outcomes.

Obesity

Most people who are overweight or obese can use dieting in combination with physical exercise to lose weight. Diets to promote weight loss are divided into four categories: low-fat, low-carbohydrate, low-calorie, and very low calorie. A meta-analysis of six randomized controlled trials found no difference between the main diet types (low calorie, low carbohydrate, and low fat), with a 2–4 kilogram weight loss in all studies. After two years, all of the diets in the studies that reduced calories resulted in equal weight loss regardless of whether changes in fat or carbohydrate consumption were emphasized.

Gluten-related disorders

Gluten, a mixture of proteins found in wheat and related grains including barley, rye, oat, and all their species and hybrids (such as spelt, kamut, and triticale), causes health problems for those with gluten-related disorders, including celiac disease, non-celiac gluten sensitivity, gluten ataxia, dermatitis herpetiformis, and wheat allergy. In these people, the gluten-free diet is the only available treatment.

Epilepsy

The ketogenic diet is a treatment to reduce epileptic seizures for adults and children when managed by a health care team.

Reduced disease risk

There may be a relationship between lifestyle including food consumption and lowering the risk of cancer and other chronic diseases. A diet high in fruit and vegetables appears to decrease the risk of cardiovascular disease and death, but not cancer.

Eating a healthy diet and getting enough exercise can maintain body weight within the normal range and prevent obesity in most people, and thus prevent the chronic diseases and poor outcomes associated with obesity.

Unhealthy diets

An unhealthy diet is a major risk factor for a number of chronic diseases including: high blood pressure, high cholesterol, diabetes, abnormal blood lipids, overweight/obesity, cardiovascular diseases, and cancer. The World Health Organization has estimated that 2.7 million deaths each year are attributable to a diet low in fruit and vegetables during the 21st century. Globally, such diets are estimated to cause about 19% of gastrointestinal cancer, 31% of ischaemic heart disease, and 11% of strokes, thus making it one of the leading preventable causes of death worldwide, and the 4th leading risk factor for any disease. As an example, the Western pattern diet is "rich in red meat, dairy products, processed and artificially sweetened foods, and salt, with minimal intake of fruits, vegetables, fish, legumes, and whole grains," contrasted by the Mediterranean diet which is associated with less morbidity and mortality.

Fad diet

Some publicized diets, often referred to as fad diets, make exaggerated claims of fast weight loss or other health advantages, such as longer life or detoxification without clinical evidence; many fad diets are based on highly restrictive or unusual food choices. Celebrity endorsements (including celebrity doctors) are frequently associated with such diets, and the individuals who develop and promote these programs often profit considerably.

Public health

Consumers are generally aware of the elements of a healthy diet, but find nutrition labels and diet advice in popular media confusing. Fears of high cholesterol were frequently voiced up until the mid-1990s. Later research shows that the distinction between high- and low-density lipoprotein ('good' and 'bad' cholesterol, respectively) is vital when considering the potential ill effects of cholesterol.

Different types of dietary fat have different effects on blood levels of cholesterol. For example, polyunsaturated fats tend to decrease both types of cholesterol; monounsaturated fats tend to lower LDL and raise HDL; saturated fats tend to either raise HDL, or raise both HDL and LDL; and trans fat tend to raise LDL and lower HDL.

Dietary cholesterol is only found in animal products such as meat, eggs, and dairy. The effect of dietary cholesterol on blood cholesterol levels is controversial. Some studies have found a link between cholesterol consumption and serum cholesterol levels. Other studies have not found a link between eating cholesterol and blood levels of cholesterol.

Vending machines in particular have come under fire as being avenues of entry into schools for junk food promoters, but there is little in the way of regulation and it is difficult for most people to properly analyze the real merits of a company referring to itself as "healthy." The Committee of Advertising Practice in the United Kingdom launched a proposal to limit media advertising for food and soft drink products high in fat, salt or sugar. The British Heart Foundation released its own government-funded advertisements, labeled "Food4Thought", which were targeted at children and adults to discourage unhealthy habits of consuming junk food.

From a psychological and cultural perspective, a healthier diet may be difficult to achieve for people with poor eating habits. This may be due to tastes acquired in childhood and preferences for sugary, salty and fatty foods. In 2018, the UK chief medical officer recommended that sugar and salt be taxed to discourage consumption. The UK government 2020 Obesity Strategy encourages healthier choices by restricting point-of-sale promotions of less-healthy foods and drinks.

Other animals

Animals that are kept by humans also benefit from a healthy diet, but the requirements of such diets may be very different from the ideal human diet.

Organomercury

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Organomercury 
 

Organomercury compounds contain at least one carbon bonded to a mercury atom, shown here.

Organomercury refers to the group of organometallic compounds that contain mercury. Typically the Hg–C bond is stable toward air and moisture but sensitive to light. Important organomercury compounds are the methylmercury(II) cation, CH₃Hg⁺; ethylmercury(II) cation, C₂H₅Hg⁺; dimethylmercury, (CH₃)₂Hg, diethylmercury, and merbromin ("Mercurochrome"). Thiomersal is used as a preservative for vaccines and intravenous drugs.

The toxicity of organomercury compounds presents both dangers and benefits. Dimethylmercury in particular, is notoriously toxic, but found use as an antifungal agent and insecticide. Merbromin and phenylmercuric borate are used as topical antiseptics, while Nitromersol is used as a preservative for vaccines and antitoxins.

Synthesis

Organomercury compounds are generated by many methods, including the direct reaction of hydrocarbons and mercury(II) salts. In this regard, organomercury chemistry more closely resembles organopalladium chemistry and contrasts with organocadmium compounds.

Mercuration of aromatic rings

Electron-rich arenes undergo direct mercuration upon treatment with Hg(O₂CCH₃)₂. The one acetate group that remains on mercury can be displaced by chloride:

C₆H₅OH + Hg(O₂CCH₃)₂ → C₆H₄(OH)–2-HgO₂CCH₃ + CH₃CO₂H

C₆H₄(OH)–2–HgO₂CCH₃ + NaCl → C₆H₄(OH)–2-HgCl + NaO₂CCH₃

The first such reaction, including a mercuration of benzene itself was reported by Otto Dimroth between 1898 and 1902.

Addition to alkenes

The Hg²⁺ center binds to alkenes, inducing the addition of hydroxide and alkoxide. For example, treatment of methyl acrylate with mercuric acetate in methanol gives an α--mercuri ester:

Hg(O₂CCH₃)₂ + CH₂=CHCO₂CH₃ → CH₃OCH₂CH(HgO₂CCH₃)CO₂CH₃

The resulting Hg-C bond can be cleaved with bromine to give the corresponding alkyl bromide:

CH₃OCH₂CH(HgO₂CCH₃)CO₂CH₃ + Br₂ → CH₃OCH₂CHBrCO₂CH₃ + BrHgO₂CCH₃

This reaction is called the Hofmann-Sand Reaction.

Reaction of Hg(II) compounds with carbanion equivalents

A general synthetic route to organomercury compounds entails alkylation with Grignard reagents and organolithium compounds. Diethylmercury results from the reaction of mercury chloride with two equivalents of ethylmagnesium bromide, a conversion that would typically be conducted in diethyl ether solution. The resulting (CH₃CH₂)₂Hg is a dense liquid (2.466 g/cm³) that boils at 57 °C at 16 torr. The compound is slightly soluble in ethanol and soluble in ether.

Similarly, diphenylmercury (m.p. 121–123 °C) can be prepared by reaction of mercury chloride and phenylmagnesium bromide. A related preparation entails formation of phenylsodium in the presence of mercury(II) salts.

Other methods

Hg(II) can be alkylated by treatment with diazonium salts in the presence of copper metal. In this way 2-chloromercuri-naphthalene has been prepared.

Phenyl(trichloromethyl)mercury can be prepared by generating dichlorocarbene in the presence of phenylmercuric chloride. A convenient carbene source is sodium trichloroacetate. This compound on heating releases dichlorocarbene:

C₆H₅HgCCl₃ → C₆H₅HgCl + CCl₂

Reactions

Organomercury compounds are versatile synthetic intermediates due to the well controlled conditions under which they undergo cleavage of the Hg-C bonds. Diphenylmercury is a source of the phenyl radical in certain syntheses. Treatment with aluminium gives triphenyl aluminium:

3 Ph₂Hg + 2 Al → (AlPh₃)₂ + 3 Hg

As indicated above, organomercury compounds react with halogens to give the corresponding organic halide. Organomercurials are commonly used in transmetalation reactions with lanthanides and alkaline-earth metals.

Cross coupling of organomercurials with organic halides is catalyzed by palladium, which provides a method for C-C bond formation. Usually of low selectivity, but if done in the presence of halides, selectivity increases. Carbonylation of lactones has been shown to employ Hg(II) reagents under palladium catalyzed conditions. (C-C bond formation and Cis ester formation).

Applications

Due to their toxicity and low nucleophilicity, organomercury compounds find limited use. The oxymercuration reaction of alkenes to alcohols using mercuric acetate proceeds via organomercury intermediates. A related reaction forming phenols is the Wolffenstein–Böters reaction. The toxicity is useful in antiseptics such as thiomersal and merbromin, and fungicides such as ethylmercury chloride and phenylmercury acetate.


Thiomersal (Merthiolate) is a well-established antiseptic and antifungal agent.

Mercurial diuretics such as mersalyl acid were once in common use, but have been superseded by the thiazides and loop diuretics, which are safer and longer-acting, as well as being orally active.

Thiol affinity chromatography

Thiols are also known as mercaptans due to their propensity for mercury capture. Thiolates (R-S⁻) and thioketones (R₂C=S), being soft nucleophiles, form strong coordination complexes with mercury(II), a soft electrophile. This mode of action makes them useful for affinity chromatography to separate thiol-containing compounds from complex mixtures. For example, organomercurial agarose gel or gel beads are used to isolate thiolated compounds (such as thiouridine) in a biological sample.

Mercury poisoning

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Mercury_poisoning 

Mercury poisoning
Other names	Mercury toxicity, mercury overdose, mercury intoxication, hydrargyria, mercurialism
The bulb of a mercury-in-glass thermometer
Specialty	Toxicology
Symptoms	Muscle weakness, poor coordination, numbness in the hands and feet
Complications	Kidney problems, decreased intelligence
Causes	Exposure to mercury
Diagnostic method	Difficult
Prevention	Decreasing use of mercury, low mercury diet
Medication	Acute poisoning: dimercaptosuccinic acid (DMSA), dimercaptopropane sulfonate (DMPS)

Mercury poisoning is a type of metal poisoning due to exposure to mercury. Symptoms depend upon the type, dose, method, and duration of exposure. They may include muscle weakness, poor coordination, numbness in the hands and feet, skin rashes, anxiety, memory problems, trouble speaking, trouble hearing, or trouble seeing. High-level exposure to methylmercury is known as Minamata disease. Methylmercury exposure in children may result in acrodynia (pink disease) in which the skin becomes pink and peels. Long-term complications may include kidney problems and decreased intelligence. The effects of long-term low-dose exposure to methylmercury are unclear.

Forms of mercury exposure include metal, vapor, salt, and organic compound. Most exposure is from eating fish, amalgam-based dental fillings, or exposure at work. In fish, those higher up in the food chain generally have higher levels of mercury. Less commonly, poisoning may occur as a method of attempted suicide. Human activities that release mercury into the environment include the burning of coal and mining of gold. Tests of the blood, urine, and hair for mercury are available but do not relate well to the amount in the body.

Prevention includes eating a diet low in mercury, removing mercury from medical and other devices, proper disposal of mercury, and not mining further mercury. In those with acute poisoning from inorganic mercury salts, chelation with either dimercaptosuccinic acid (DMSA) or dimercaptopropane sulfonate (DMPS) appears to improve outcomes if given within a few hours of exposure. Chelation for those with long-term exposure is of unclear benefit. In certain communities that survive on fishing, rates of mercury poisoning among children have been as high as 1.7 per 100.

Signs and symptoms

Common symptoms of mercury poisoning include peripheral neuropathy, presenting as paresthesia or itching, burning, pain, or even a sensation that resembles small insects crawling on or under the skin (formication); skin discoloration (pink cheeks, fingertips and toes); swelling; and desquamation (shedding or peeling of skin).

Mercury irreversibly inhibits selenium-dependent enzymes (see below) and may also inactivate S-adenosyl-methionine, which is necessary for catecholamine catabolism by catechol-O-methyl transferase. Due to the body's inability to degrade catecholamines (e.g. adrenaline), a person suffering from mercury poisoning may experience profuse sweating, tachycardia (persistently faster-than-normal heart beat), increased salivation, and hypertension (high blood pressure).

Affected children may show red cheeks, nose and lips, loss of hair, teeth, and nails, transient rashes, hypotonia (muscle weakness), and increased sensitivity to light. Other symptoms may include kidney dysfunction (e.g. Fanconi syndrome) or neuropsychiatric symptoms such as emotional lability, memory impairment, or insomnia.

Thus, the clinical presentation may resemble pheochromocytoma or Kawasaki disease. Desquamation (skin peeling) can occur with severe mercury poisoning acquired by handling elemental mercury.

Causes

The consumption of fish is by far the most significant source of ingestion-related mercury exposure in humans, although plants and livestock also contain mercury due to bioconcentration of organic mercury from seawater, freshwater, marine and lacustrine sediments, soils, and atmosphere, and due to biomagnification by ingesting other mercury-containing organisms. Exposure to mercury can occur from breathing contaminated air, from eating foods that have acquired mercury residues during processing, from exposure to mercury vapor in mercury amalgam dental restorations, and from improper use or disposal of mercury and mercury-containing objects, for example, after spills of elemental mercury or improper disposal of fluorescent lamps.

All of these, except elemental liquid mercury, produce toxicity or death with less than a gram. Mercury's zero oxidation state (Hg⁰) exists as vapor or as liquid metal, its mercurous state (Hg⁺) exists as inorganic salts, and its mercuric state (Hg²⁺) may form either inorganic salts or organomercury compounds.

Consumption of whale and dolphin meat, as is the practice in Japan, is a source of high levels of mercury poisoning. Tetsuya Endo, a professor at the Health Sciences University of Hokkaido, has tested whale meat purchased in the whaling town of Taiji and found mercury levels more than 20 times the acceptable Japanese standard.

Human-generated sources, such as coal-burning power plants emit about half of atmospheric mercury, with natural sources such as volcanoes responsible for the remainder. An estimated two-thirds of human-generated mercury comes from stationary combustion, mostly of coal. Other important human-generated sources include gold production, nonferrous metal production, cement production, waste disposal, human crematoria, caustic soda production, pig iron and steel production, mercury production (mostly for batteries), and biomass burning.

Small independent gold-mining operation workers are at higher risk of mercury poisoning because of crude processing methods. Such is the danger for the galamsey in Ghana and similar workers known as orpailleurs in neighboring francophone countries. While no official government estimates of the labor force have been made, observers believe 20,000–50,000 work as galamseys in Ghana, a figure including many women, who work as porters. Similar problems have been reported amongst the gold miners of Indonesia.

Some mercury compounds, especially organomercury compounds, can also be readily absorbed through direct skin contact. Mercury and its compounds are commonly used in chemical laboratories, hospitals, dental clinics, and facilities involved in the production of items such as fluorescent light bulbs, batteries, and explosives.

Many traditional medicines, including ones used in Ayurvedic medicine and Traditional Chinese medicine, contain mercury and other heavy metals.

No scientific data support the claim that mercury compounds in vaccine preservatives cause autism or its symptoms.

Sources

Compounds of mercury tend to be much more toxic than either the elemental form or the salts. These compounds have been implicated in causing brain and liver damage. The most dangerous mercury compound, dimethylmercury, is so toxic that even a few microliters spilled on the skin, or even on a latex glove, can cause death.

Methylmercury and related organomercury compounds

Methylmercury is the major source of organic mercury for all individuals. Due to bioaccumulation it works its way up through the food web and thus biomagnifies, resulting in high concentrations among populations of some species. Top predatory fish, such as tuna or swordfish, are usually of greater concern than smaller species. The US FDA and the EPA advise women of child-bearing age, nursing mothers, and young children to completely avoid swordfish, shark, king mackerel and tilefish from the Gulf of Mexico, and to limit consumption of albacore ("white") tuna to no more than 170 g (6 oz) per week, and of all other fish and shellfish to no more than 340 g (12 oz) per week. A 2006 review of the risks and benefits of fish consumption found, for adults, the benefits of one to two servings of fish per week outweigh the risks, even (except for a few fish species) for women of childbearing age, and that avoidance of fish consumption could result in significant excess coronary heart disease deaths and suboptimal neural development in children.

Because the process of mercury-dependent sequestration of selenium is slow, the period between exposure to methylmercury and the appearance of symptoms in adult poisoning cases tends to be extended. The longest recorded latent period is five months after a single exposure, in the Dartmouth case (see History); other latent periods in the range of weeks to months have also been reported. When the first symptom appears, typically paresthesia (a tingling or numbness in the skin), it is followed rapidly by more severe effects, sometimes ending in coma and death. The toxic damage appears to be determined by the peak value of mercury, not the length of the exposure.

Methylmercury exposure during rodent gestation, a developmental period that approximately models human neural development during the first two trimesters of gestation, has long-lasting behavioral consequences that appear in adulthood and, in some cases, may not appear until aging. Prefrontal cortex or dopamine neurotransmission could be especially sensitive to even subtle gestational methylmercury exposure and suggests that public health assessments of methylmercury based on intellectual performance may underestimate the impact of methylmercury in public health.

Ethylmercury is a breakdown product of the antibacteriological agent ethylmercurithiosalicylate, which has been used as a topical antiseptic and a vaccine preservative (further discussed under Thiomersal below). Its characteristics have not been studied as extensively as those of methylmercury. It is cleared from the blood much more rapidly, with a half-life of seven to ten days, and it is metabolized much more quickly than methylmercury. It is presumed not to have methylmercury's ability to cross the blood–brain barrier via a transporter, but instead relies on simple diffusion to enter the brain. Other exposure sources of organic mercury include phenylmercuric acetate and phenylmercuric nitrate. These compounds were used in indoor latex paints for their antimildew properties, but were removed in 1990 because of cases of toxicity.

Inorganic mercury compounds

Mercury occurs as salts such as mercuric chloride (HgCl₂) and mercurous chloride (Hg₂Cl₂), the latter also known as calomel. Because they are more soluble in water, mercuric salts are usually more acutely toxic than mercurous salts. Their higher solubility lets them be more readily absorbed from the gastrointestinal tract. Mercury salts affect primarily the gastrointestinal tract and the kidneys, and can cause severe kidney damage; however, as they cannot cross the blood–brain barrier easily, these salts inflict little neurological damage without continuous or heavy exposure. Mercuric cyanide (Hg(CN)₂) is a particularly toxic mercury compound that has been used in murders, as it contains not only mercury but also cyanide, leading to simultaneous cyanide poisoning. The drug n-acetyl penicillamine has been used to treat mercury poisoning with limited success.

Elemental mercury

Quicksilver (liquid metallic mercury) is poorly absorbed by ingestion and skin contact. Its vapor is the most hazardous form. Animal data indicate less than 0.01% of ingested mercury is absorbed through the intact gastrointestinal tract, though it may not be true for individuals suffering from ileus. Cases of systemic toxicity from accidental swallowing are rare, and attempted suicide via intravenous injection does not appear to result in systemic toxicity, though it still causes damage by physically blocking blood vessels both at the site of injection and the lungs. Though not studied quantitatively, the physical properties of liquid elemental mercury limit its absorption through intact skin and in light of its very low absorption rate from the gastrointestinal tract, skin absorption would not be high. Some mercury vapor is absorbed dermally, but uptake by this route is only about 1% of that by inhalation.

In humans, approximately 80% of inhaled mercury vapor is absorbed via the respiratory tract, where it enters the circulatory system and is distributed throughout the body. Chronic exposure by inhalation, even at low concentrations in the range 0.7–42 μg/m³, has been shown in case–control studies to cause effects such as tremors, impaired cognitive skills, and sleep disturbance in workers.

Acute inhalation of high concentrations causes a wide variety of cognitive, personality, sensory, and motor disturbances. The most prominent symptoms include tremors (initially affecting the hands and sometimes spreading to other parts of the body), emotional lability (characterized by irritability, excessive shyness, confidence loss, and nervousness), insomnia, memory loss, neuromuscular changes (weakness, muscle atrophy, muscle twitching), headaches, polyneuropathy (paresthesia, stocking-glove sensory loss, hyperactive tendon reflexes, slowed sensory and motor nerve conduction velocities), and performance deficits in tests of cognitive function.

Mechanism

The toxicity of mercury sources can be expected to depend on its nature, i.e., salts vs. organomercury compounds vs. elemental mercury.

The primary mechanism of mercury toxicity involves its irreversible inhibition of selenoenzymes, such as thioredoxin reductase (IC50 = 9 nM). Although it has many functions, thioredoxin reductase restores vitamins C and E, as well as a number of other important antioxidant molecules, back into their reduced forms, enabling them to counteract oxidative damage. Since the rate of oxygen consumption is particularly high in brain tissues, production of reactive oxygen species (ROS) is accentuated in these vital cells, making them particularly vulnerable to oxidative damage and especially dependent upon the antioxidant protection provided by selenoenzymes. High mercury exposures deplete the amount of cellular selenium available for the biosynthesis of thioredoxin reductase and other selenoenzymes that prevent and reverse oxidative damage, which, if the depletion is severe and long lasting, results in brain cell dysfunctions that can ultimately cause death.

Mercury in its various forms is particularly harmful to fetuses as an environmental toxin in pregnancy, as well as to infants. Women who have been exposed to mercury in substantial excess of dietary selenium intakes during pregnancy are at risk of giving birth to children with serious birth defects. Mercury exposures in excess of dietary selenium intakes in young children can have severe neurological consequences, preventing nerve sheaths from forming properly.

Exposure to methylmercury causes increased levels of antibodies sent to myelin basic protein (MBP), which is involved in the myelination of neurons, and glial fibrillary acidic protein (GFAP), which is essential to many central nervous system (CNS). This causes an autoimmmune response against MBP and GFAP and results in the degradation of neural myelin and general decline in function of the CNS.

Diagnosis

Diagnosis of elemental or inorganic mercury poisoning involves determining the history of exposure, physical findings, and an elevated body burden of mercury. Although whole-blood mercury concentrations are typically less than 6 μg/L, diets rich in fish can result in blood mercury concentrations higher than 200 μg/L; it is not that useful to measure these levels for suspected cases of elemental or inorganic poisoning because of mercury's short half-life in the blood. If the exposure is chronic, urine levels can be obtained; 24-hour collections are more reliable than spot collections. It is difficult or impossible to interpret urine samples of patients undergoing chelation therapy, as the therapy itself increases mercury levels in the samples.

Diagnosis of organic mercury poisoning differs in that whole-blood or hair analysis is more reliable than urinary mercury levels.

Prevention

Mercury poisoning can be prevented or minimized by eliminating or reducing exposure to mercury and mercury compounds. To that end, many governments and private groups have made efforts to heavily regulate the use of mercury, or to issue advisories about the use of mercury. Most countries have signed the Minamata Convention on Mercury.

The export from the European Union of mercury and some mercury compounds has been prohibited since 15 March 2010. The European Union has banned most uses of mercury. Mercury is allowed for fluorescent light bulbs because of pressure from countries such as Germany, the Netherlands and Hungary, which are connected to the main producers of fluorescent light bulbs: General Electric, Philips and Osram.

US environmental limits

Country	Regulating agency	Regulated activity	Medium	Type of mercury compound	Type of limit	Limit
US	Occupational Safety and Health Administration	occupational exposure	air	elemental mercury	Ceiling (not to exceed)	0.1 mg/m3
US	Occupational Safety and Health Administration	occupational exposure	air	organic mercury	Ceiling (not to exceed)	0.05 mg/m3
US	Food and Drug Administration	eating	sea food	methylmercury	Maximum allowable concentration	1 ppm (1 mg/L)
US	Environmental Protection Agency	drinking	water	inorganic mercury	Maximum contaminant level	2 ppb (0.002 mg/L)

The United States Environmental Protection Agency (EPA) issued recommendations in 2004 regarding exposure to mercury in fish and shellfish. The EPA also developed the "Fish Kids" awareness campaign for children and young adults  on account of the greater impact of mercury exposure to that population.

Cleaning spilled mercury

EPA workers clean up residential mercury spill in 2004

Mercury thermometers and mercury light bulbs are not as common as they used to be, and the amount of mercury they contain is unlikely to be a health concern if handled carefully. However, broken items still require careful cleanup, as mercury can be hard to collect and it is easy to accidentally create a much larger exposure problem. If available, powdered sulfur may be applied to the spill, in order to create a solid compound that is more easily removed from surfaces than liquid mercury.

Treatment

Identifying and removing the source of the mercury is crucial. Decontamination requires removal of clothes, washing skin with soap and water, and flushing the eyes with saline solution as needed.

Chelation therapy

Chelation therapy for acute inorganic mercury poisoning, a formerly common method, was done with DMSA, 2,3-dimercapto-1-propanesulfonic acid (DMPS), D-penicillamine (DPCN), or dimercaprol (BAL). Only DMSA is FDA-approved for use in children for treating mercury poisoning. However, several studies found no clear clinical benefit from DMSA treatment for poisoning due to mercury vapor. No chelator for methylmercury or ethylmercury is approved by the FDA; DMSA is the most frequently used for severe methylmercury poisoning, as it is given orally, has fewer side-effects, and has been found to be superior to BAL, DPCN, and DMPS. α-Lipoic acid (ALA) has been shown to be protective against acute mercury poisoning in several mammalian species when it is given soon after exposure; correct dosage is required, as inappropriate dosages increase toxicity. Although it has been hypothesized that frequent low dosages of ALA may have potential as a mercury chelator, studies in rats have been contradictory. Glutathione and N-acetylcysteine (NAC) are recommended by some physicians, but have been shown to increase mercury concentrations in the kidneys and the brain.

Chelation therapy can be hazardous if administered incorrectly. In August 2005, an incorrect form of EDTA (edetate disodium) used for chelation therapy resulted in hypocalcemia, causing cardiac arrest that killed a five-year-old autistic boy.

Other

Experimental animal and epidemiological study findings have confirmed the interaction between selenium and methylmercury. Instead of causing a decline in neurodevelopmental outcomes, epidemiological studies have found that improved nutrient (i.e., omega-3 fatty acids, selenium, iodine, vitamin D) intakes as a result of ocean fish consumption during pregnancy improves maternal and fetal outcomes. For example, increased ocean fish consumption during pregnancy was associated with 4-6 point increases in child IQs.

Prognosis

Some of the toxic effects of mercury are partially or wholly reversible provided specific therapy is able to restore selenium availability to normal before tissue damage from oxidation becomes too extensive. Autopsy findings point to a half-life of inorganic mercury in human brains of 27.4 years. Heavy or prolonged exposure can do irreversible damage, in particular in fetuses, infants, and young children. Young's syndrome is believed to be a long-term consequence of early childhood mercury poisoning.

Mercuric chloride may cause cancer as it has caused increases in several types of tumors in rats and mice, while methyl mercury has caused kidney tumors in male rats. The EPA has classified mercuric chloride and methyl mercury as possible human carcinogens (ATSDR, EPA)

Detection in biological fluids

Mercury may be measured in blood or urine to confirm a diagnosis of poisoning in hospitalized people or to assist in the forensic investigation in a case of fatal over dosage. Some analytical techniques are capable of distinguishing organic from inorganic forms of the metal. The concentrations in both fluids tend to reach high levels early after exposure to inorganic forms, while lower but very persistent levels are observed following exposure to elemental or organic mercury. Chelation therapy can cause a transient elevation of urine mercury levels.

History

• Several Chinese emperors and other Chinese nobles are known or suspected to have died or been sickened by mercury poisoning after alchemists administered them "elixirs" to promote health, longevity, or immortality that contained either elemental mercury or (more commonly) cinnabar. Among the most prominent examples:
  • The first emperor of unified China, Qin Shi Huang, it is reported, died in 210 BC of ingesting mercury pills that were intended to give him eternal life.
  • Emperor Xuānzong of Tang, one of the emperors of the late Tang dynasty of China, was prescribed "cinnabar that had been treated and subdued by fire" to achieve immortality. Concerns that the prescription was having ill effects on the emperor's health and sanity were waved off by the imperial alchemists, who cited medical texts listing a number of the emperor's conditions (including itching, formication, swelling, and muscle weakness), today recognized as signs and symptoms of mercury poisoning, as evidence that the elixir was effectively treating the emperor's latent ailments. Xuānzong became irritable and paranoid, and he seems to have ultimately died in 859 from the poisoning.
• During the Spanish conquest of the New World in the 16th and 17th centuries, slave mining of mercury deposits was common because the metal was used to purify the rich silver deposits in South America before being shipped back to Spain. To avoid the effects of mercury poisoning on their children, parents were known to purposefully maim their children to make them unable to work in the mines.
• The phrase mad as a hatter is likely a reference to mercury poisoning among milliners (so-called "mad hatter disease"), as mercury-based compounds were once used in the manufacture of felt hats in the 18th and 19th century. (The Mad Hatter character of Alice in Wonderland was, it is presumed, inspired by an eccentric furniture dealer named Theophilus Carter. Carter was not a victim of mad hatter disease although Lewis Carroll would have been familiar with the phenomenon of dementia that occurred among hatters.)
• In 1810, two British ships, HMS Triumph and HMS Phipps, salvaged a large load of elemental mercury from a wrecked Spanish vessel near Cadiz, Spain. The bladders containing the mercury soon ruptured. The element spread about the ships in liquid and vapor forms. The sailors presented with neurologic compromises: tremor, paralysis, and excessive salivation as well as tooth loss, skin problems, and pulmonary complaints. In 1823 William Burnet, MD published a report on the effects of Mercurial vapor. The Triumph’s surgeon, Henry Plowman, had concluded that the ailments had arisen from inhaling the mercurialized atmosphere. His treatment was to order the lower deck gun ports to be opened, when it was safe to do so; sleeping on the orlop was forbidden; and no men slept in the lower deck if they were at all symptomatic. Windsails were set to channel fresh air into the lower decks day and night.
• Historically, gold amalgam was widely used in gilding, leading to numerous casualties among the workers. It is estimated that during the construction of Saint Isaac's Cathedral alone, 60 men died from the gilding of the main dome.
• For years, including the early part of his presidency, Abraham Lincoln took a common medicine of his time called "blue mass," which contained significant amounts of mercury.
• On September 5, 1920, silent movie actress Olive Thomas ingested mercury capsules dissolved in an alcoholic solution at the Hotel Ritz in Paris. There is still controversy over whether it was suicide, or whether she consumed the external preparation by mistake. Her husband, Jack Pickford (the brother of Mary Pickford), had syphilis, and the mercury was used as a treatment of the venereal disease at the time. She died a few days later at the American Hospital in Neuilly.
• An early scientific study of mercury poisoning was in 1923–6 by the German inorganic chemist, Alfred Stock, who himself became poisoned, together with his colleagues, by breathing mercury vapor that was being released by his laboratory equipment—diffusion pumps, float valves, and manometers—all of which contained mercury, and also from mercury that had been accidentally spilt and remained in cracks in the linoleum floor covering. He published a number of papers on mercury poisoning, founded a committee in Berlin to study cases of possible mercury poisoning, and introduced the term micromercurialism.
• The term Hunter-Russell syndrome derives from a study of mercury poisoning among workers in a seed packing factory in Norwich, England in the late 1930s who breathed methylmercury that was being used as a seed disinfectant and preservative.
• Outbreaks of methylmercury poisoning occurred in several places in Japan during the 1950s due to industrial discharges of mercury into rivers and coastal waters. The best-known instances were in Minamata and Niigata. In Minamata alone, more than 600 people died due to what became known as Minamata disease. More than 21,000 people filed claims with the Japanese government, of which almost 3000 became certified as having the disease. In 22 documented cases, pregnant women who consumed contaminated fish showed mild or no symptoms but gave birth to infants with severe developmental disabilities.
• Mercury poisoning of generations of Grassy Narrows and Whitedog in Ontario who were exposed to high levels of mercury by consuming mercury-contaminated fish when Dryden Chemical Company discharged over 9,000 kilograms (20,000 lb) of mercury directly into the Wabigoon-English River system and continued with mercury air pollution until 1975.
• Widespread mercury poisoning occurred in rural Iraq in 1971–1972, when grain treated with a methylmercury-based fungicide that was intended for planting only was used by the rural population to make bread, causing at least 6530 cases of mercury poisoning and at least 459 deaths (see Basra poison grain disaster).
• On August 14, 1996, Karen Wetterhahn, a chemistry professor working at Dartmouth College, spilled a small amount of dimethylmercury on her latex glove. She began experiencing the symptoms of mercury poisoning five months later and, despite aggressive chelation therapy, died a few months later from a mercury induced neurodegenerative disease
• In April 2000, Alan Chmurny attempted to kill a former employee, Marta Bradley, by pouring mercury into the ventilation system of her car.
• On March 19, 2008, Tony Winnett, 55, inhaled mercury vapors while trying to extract gold from computer parts (by using liquid mercury to separate gold from the rest of the alloy), and died ten days later. His Oklahoma residence became so contaminated that it had to be gutted.
• In December 2008, actor Jeremy Piven was diagnosed with mercury poisoning possibly resulting from eating sushi twice a day for twenty years or from taking herbal remedies.
• In India, a study by Centre for Science and Environment and Indian Institute of Toxicology Research has found that in the country's energy capital Singrauli, mercury is slowly entering people's homes, food, water and even blood.
• The Minamata Convention on Mercury in 2016 announced that the signing of the "international treaty designed to protect human health and the environment from anthropogenic releases and emission of mercury and mercury compounds" on April 22, 2016—Earth Day. It was the sixtieth anniversary of the discovery of the disease.

Infantile acrodynia

Infantile acrodynia (also known as "calomel disease", "erythredemic polyneuropathy", and "pink disease") is a type of mercury poisoning in children characterized by pain and pink discoloration of the hands and feet. The word is derived from the Greek, where άκρο means end or extremity, and οδυνη means pain. Acrodynia resulted primarily from calomel in teething powders and decreased greatly after calomel was excluded from most teething powders in 1954.

Acrodynia is difficult to diagnose, "it is most often postulated that the etiology of this syndrome is an idiosyncratic hypersensitivity reaction to mercury because of the lack of correlation with mercury levels, many of the symptoms resemble recognized mercury poisoning."

Medicine

Mercury was once prescribed as a purgative. Many mercury-containing compounds were once used in medicines. These include calomel (mercurous chloride), and mercuric chloride.

Thiomersal

In 1999, the Centers for Disease Control (CDC) and the American Academy of Pediatrics (AAP) asked vaccine makers to remove the organomercury compound thiomersal (spelled "thimerosal" in the US) from vaccines as quickly as possible, and thiomersal has been phased out of US and European vaccines, except for some preparations of influenza vaccine. The CDC and the AAP followed the precautionary principle, which assumes that there is no harm in exercising caution even if it later turns out to be unwarranted, but their 1999 action sparked confusion and controversy that Thiomersal was the cause of autism.

Since 2000, the thiomersal in child vaccines has been alleged to contribute to autism, and thousands of parents in the United States have pursued legal compensation from a federal fund. A 2004 Institute of Medicine (IOM) committee favored rejecting any causal relationship between thiomersal-containing vaccines and autism. Autism incidence rates increased steadily even after thiomersal was removed from childhood vaccines. Currently there is no accepted scientific evidence that exposure to thiomersal is a factor in causing autism.

Dental amalgam toxicity

Dental amalgam is a possible cause of low-level mercury poisoning due to its use in dental fillings. Discussion on the topic includes debates on whether amalgam should be used, with critics arguing that its toxic effects make it unsafe.

Cosmetics

Some skin whitening products contain the toxic mercury(II) chloride as the active ingredient. When applied, the chemical readily absorbs through the skin into the bloodstream. The use of mercury in cosmetics is illegal in the United States. However, cosmetics containing mercury are often illegally imported. Following a certified case of mercury poisoning resulting from the use of an imported skin whitening product, the United States Food and Drug Administration warned against the use of such products. Symptoms of mercury poisoning have resulted from the use of various mercury-containing cosmetic products. The use of skin whitening products is especially popular amongst Asian women. In Hong Kong in 2002, two products were discovered to contain between 9,000 and 60,000 times the recommended dose.

Fluorescent lamps

Fluorescent lamps contain mercury, which is released when bulbs break. Mercury in bulbs is typically present as either elemental mercury liquid, vapor, or both, since the liquid evaporates at ambient temperature. When broken indoors, bulbs may emit sufficient mercury vapor to present health concerns, and the U.S. Environmental Protection Agency recommends evacuating and airing out a room for at least 15 minutes after breaking a fluorescent light bulb. Breakage of multiple bulbs presents a greater concern. A 1987 report described a 23-month-old toddler who suffered anorexia, weight loss, irritability, profuse sweating, and peeling and redness of fingers and toes. This case of acrodynia was traced to exposure of mercury from a carton of 8-foot fluorescent light bulbs that had broken in a potting shed adjacent to the main nursery. The glass was cleaned up and discarded, but the child often used the area to play in.

Assassination attempts

Mercury has, allegedly, been used at various times to assassinate people. In 2008, Russian lawyer Karinna Moskalenko claimed to have been poisoned by mercury left in her car, while in 2010 journalists Viktor Kalashnikov and Marina Kalashnikova accused Russia's FSB of trying to poison them.