There are many minerals which are considered nutrients and are vital for the proper functioning of the body. These are generally split into the macrominerals such as calcium, magnesium, potassium, sodium, and zinc, and the trace minerals, including selenium, iodine, boron, and molybdenum.
Equally, there are a number of minerals that are toxic to the human body and interfere with its functioning and undermine health. The group of most concern are known as the heavy metals and includes mercury, lead, cadmium, aluminium, and arsenic. The definition of what constitutes a heavy metal is vague and various criteria have been proposed based on density, atomic weight or atomic number, or various chemical properties and toxicity1. The term toxic metals has been proposed as an alternative since under many definitions nutrient metals such as zinc, copper and molybdenum actually fall under the heading of heavy metals. Of concern here is the fact that metals commonly referred to as heavy metals or toxic metals are detrimental to health for a variety of reasons and unfortunately are prevalent in the environment due in considerable part to the activities of modern society. Individuals may be exposed occupationally or due to factors such as consuming contaminated food and water (this article will focus on sources of exposure other than occupational).
N.B. "Toxic Metals" would seem to be a more accurate term so will be used from this point on
Effects of Toxic Metals in the Body
The effects of toxic metals that may result in symptoms and disease can be broken down into two distinct, yet often overlapping categories:
- Direct toxic effects that damage tissues and interfere with normal metabolic processes.
- Displacement and/or depletion of essential nutrients leading to nutritional deficiencies and associated health concerns.
Nutrition researcher Robert Goyer states that "Cadmium, lead, mercury, and aluminum are toxic metals that may interact metabolically with nutritionally essential metals."2
Among the symptoms and diseases associated with toxic metals, or heavy metal toxicity, are impairment of cognitive development (e.g. developmental disorders), degenerative diseases of the nervous system, which would include Alzheimer's disease, Parkinson's disease, and multiple sclerosis (MS), problems with skeletal development and maintenance (e.g. osteoporosis), kidney disorders, and blood disorders.
Sources of toxic metals are many and varied. They occur naturally in nature and may accumulate in the food chain and water supply due to high levels in particular locations. Anthropogenic (manmade) sources account for a large amount of the toxic metals we are exposed to in the modern day however. They are by-products of many industrial processes and often end up polluting the air we breath and the food and water we eat and drink. In 2002 the UK Drinking Water Inspectorate reported that tap water may contain contaminants including toxic metals, as well as pesticides, drugs, and chemical waste from industry.3
Mercury in its elemental form is what we see in traditional thermometers. However, there are also organic forms of mercury; organic molecules are bound to the metal. The most common organic forms of mercury are methylmercury and ethylmercury.
Sources of Mercury Exposure
Dental Amalgam Fillings - According to the US National Institutes of Health (NIH)4 these fillings, which are approximately 50% mercury by weight, are continually releasing mercury vapour which is then breathed in. Research confirms individuals with amalgam fillings have a greater body burden of mercury than those who do not.5 However, the amount of mercury an individual absorbs from their fillings varies considerably from person to person6; this makes individual testing important. Crucially for health, mercury vapour from fillings can be converted to more toxic elemental mercury and methylmercury in the body and both can accumulate in the brain.7
Food - Far and away the major problem food in relation to mercury contamination is fish. Atmospheric inorganic mercury from natural and industrial sources is absorbed by large bodies of water where it is converted by bacteria into organic methylmercury, the most toxic form.8 This methylmercury then enters the food chain and reaches high levels in large predatory fish such as shark, swordfish, tuna, and king mackeral. Many authorities such as the Food Standards Agency (FSA) in the UK have now advised the public, particularlly pregnant women, to limit their intake of fish.9 Other foods have in the past been contaminated with mercury due to the use of organomercury seed dressings; this increased the mercury content of the crops themselves and also of meat and dairy products of animals fed these crops.10 These mercury compounds have now been banned in agriculture.
Water - Municipal water supplies are rarely contaminated with mercury but that's not to say it doesn't ever happen. Mercury can enter the water supply as a result of precipitation (rain, snow etc) depositing atmospheric mercury, as a result of naturally occuring mercury being released from rock and soil, and via contamination from industrial sites and agricultural sites. Most of the mercury found in the water supply is inorganic but again, some of this can be converted to methylmercury by bacteria.11
Air Pollution - Mercury pollution of the air comes from a few major sources; the combustion of fossil fuels (as in coal and gas-fired power stations), release from metal smelters, and from the incineration of mercury-containing products, such as electronic devices and batteries.11 In the US, using data submitted by power companies to the Environmental Protection Agency (EPA), the non-profit Environmental Working Group reported that in 1999 about 98,000 lbs (49 tons) of mercury were emiited directly into the atmosphere by coal-burning power plants.12 The US and other nations have now enacted regulations on mercury emissions (or are in the process of doing so).
Vaccines - Due to much media attention in relation to autism and a possible connection to vaccinations many people will have heard of thimerosal. This is a mercury-containing additive that was used in many vaccines as a preservative. Due to pressue from autism groups and others however, it has now been removed from the majority of vaccines in the US and other countries.
Health Effects of Mercury
As mentioned previously, the most toxic form of mercury is methylmercury which is easily absorbed and harder for the body to rid itself of than other forms. Mercury is particularly toxic to the nervous system, damaging brain cells and interfering with communication between them are just some of its effects.13 Chronic fatigue, depression, and poor memory are all signs of mercury toxicity.14 Mercury chronically activates the immune system and leads to the development of autoantibodies (antibodies which cause autoimmune diseases).15 High mercury hair concentrations have been linked to metabolic syndrome; causing inefficient insulin function and imbalanced blood sugar levels.16 This is a situation that can ultimately lead to the development of type-2 diabetes mellitus.
Methylmercury is 5 to 10 times more toxic to developing embryos than it is to adults; in its 2000 report on the toxicological effects of methylmercury the National Research Council, concluded that the population at highest risk of mercury toxicity are children of women who consume large amounts of fish and seafood.8 The report estimated that more than 60,000 children born each year in the US are at risk for adverse neurodevelopmental effects due to exposure to methylmercury in the womb.
Lead is both a "heavy metal", by any definition, and also a toxic metal.
Sources of Lead Exposure
Lead Paint - Lead was used in paints produced for use in homes and public buildings for many years until its toxicity became apparent. It was primarily used as a white or yellow pigment but also to reduce drying time, increase durability, resist moisture, and help the paint retain a fresh appearance.17 It is vital to ensure that children do not chew on areas painted with lead paint or eat pieces that have cracked and broken off.
House Dust - Lead from broken off pieces of lead paint or that has been walked in with contaminated soil from outdoors can contribute to significant amounts of lead in house dust.18 Since house dust is continually being breathed in this can contribute to an individual's body burden of this toxic metal. Again, children must be watched to make sure they are not licking dusty surfaces etc. To reduce the amount of lead present in your home in the form of dust you should vacuum and clean surfaces regularly, washing or disposing of cleaning materials immediately.
Soil - Lead can often been found in soil next to buildings finished with lead paint, near busy roads, and near industrial areas and companies that use lead.18 To reduce the risk of bringing lead into your home you can place washable rugs at each door and wash them seperately from clothing and other items. Also taking off shoes at the door so as not to walk lead-contaminated soil into the home is a good idea.
Food - Plants usually do not absorb lead unless there is significant amounts in the soil e.g. if crops are grown on contaminated ground, old industrial areas for example.18 Animal foods can become more easily contaminated as livestock will tend to chew, lick, and eat anything; lead paint, bonfire ash, lead piping, flashing, and soil are amongst the common sources.19
Water - In older homes the piping that brings water into the building can be a significant source of lead. In older homes lead was the material of choice for plumbing pipes and only in recent decades has lead-containing solder (used on copper pipes) been replaced by lead-free solder and plastic piping that doesn't require soldering.18 If your home was built more than 30 years ago there is a good chance it may have some lead piping. Some types of water, particularly soft water from upland areas, can pick up lead from these pipes before it reaches the tap; lead deposits may also build up in the pipes and then be dislodged which can cause high lead levels in the water supply.20
Air Pollution - Outdoor air levels of lead have not been a significant issue in developed nations since the 1980s when unleaded petrol/gas was widely introduced. Developing nations however still use leaded petrol, which is something to be aware of when travelling. Lead air pollution can still pose a problem in developed countries in the vicinity of smelters and industries using lead where air concentrations can sometimes exceed national safety limits.22 Because lead is heavy, it does not hang around in the air for long so gets deposited in soil and bodyies of water quickly. It is therefore also found mainly near its source.
Cosmetics - Believe it or not, lead is commonly found in quite significant levels in lipstick. This has been verified by testing of a range of brands by the US Food and Drug Administration (FDA) and by campaign groups including the Campaign for Safe Cosmetics (CSC).
Health Effects of Lead
According to the Occupational Safety and Health Administration (OSHA) of the United States Department of Labor, lead exposure both acute (a few days) and chronic (several years) adversely affects numerous body systems and causes many forms of health impairment and disease.23 The OSHA states that: "The frequency and severity of medical symptoms increases with the concentration of lead in the blood. Common symptoms of acute lead poisoning are loss of appetite, nausea, vomiting, stomach cramps, constipation, difficulty in sleeping, fatique, moodiness, headache, joint or muscle aches, anemia, and decreased sexual drive. Acute health poisoning from uncontrolled occupational exposures has resulted in fatalities. Long term (chronic) overexposure to lead may result in severe damage to the blood-forming, nervous, urinary, and reproductive systems."
Research has shown that blood lead levels below those considered safe by the World Health Organization (WHO) in 2004 (<10mcg/dl) can cause significant cognitive and intellectual impairment in children.24 However, the effects of lead at these levels are small when compard to the effects social and parental environments have on a child's intellectual development. In adults and the elderly it has been found that lead accumulates in bone and can subsequently be re-released, causing toxic effects in soft tissues.25 Higher cumulative lead exposure and bone concentrations are associated with more rapid cognitive decline26, an increased risk of hypertension (high blood pressure) 27, and an increased risk of renal insufficiency (kidney disease).25
Cadmium is present in the environment and is also widely used in industry and the manufacture of many modern consumer goods.
Sources of Cadmium
Smoking - The tobacco plant is one of a group of crops that are particularly efficient at taking up and storing cadmium from the soil.28 Cigarette smoking therefore significantly increases the amount of cadmium in the body.29
Air Pollution - Due to its widespread use in industry, substantial amounts of cadmium end up in the air. The major source of airborne cadmium is smelters but other significant sources include the burning of fossil fuels and the incineration of municipal waste containing cadmium such as plastics and nickel-cadmium (NiCd) batteries; airborne cadmium may also be derived from iron and steel works.28
Food - Cadmium can be carried substantial distances in the in the atmosphere but is eventually deposited in soil, making food a major source of cadmium. Cadmium is also present in phosphate fertilisers and sewage sludge which add to the content of agricultural soil. Cadmium is taken up easily by crops such as leafy vegetables, root crops, cereals and grains. Rice, other cereal grains, potatoes, and other vegetables take up cadmium much more easily than they do other toxic metals including mercury and lead.28 Cadmium can also contaminate meat, particularly organ meats, and in some areas elevated levels have been found in shellfish. 30
Water - According to the EPA the major sources of cadmium in the drinking water supply are: "...corrosion of galvanized pipes; erosion of natural deposits; discharge from metal refineries; runoff from waste batteries and paints. "31 Natural deposits of cadmium in rock and soil are more likely to be eroded when water is soft or acidic.28 Cadmium concentrations in municipal water supplies are regulated in the US and other developed countries but traces are inevitable and consumption of cadmium in drinking water over time may be a health concern. If you fear that run off may have infected your nearby water supply it might be a good idea to learn more information about nearby metal refineries.
Health Effects of Cadmium
Smokers are by far the group most at risk from cadmium toxicity with lung absorption being about 50% compared to only a few per cent of cadmium ingested in food or water being absorbed. This is not to say that consumption of cadmium contaminated food and water over time does not have a deleterious effect on health. Cadmium tends to accumulate in the kidneys and is associated with renal damage.32 Even at low concentrations found widely in the general population due to the sources discussed above, cadmium can result in kidney disease and both lower bone mineral density (BMD) and increased risk of fractures, both signs of osteoporosis.33 Along with the kidneys and bones, the other major target organs for cadmium toxicity are the lungs. Acute exposure (usually occupational) is associated with bronchitis, pulmonary oedema, and chemical pneumonitis. 34 Research has also shown a significant association between cadmium toxicity and neurobehavioural deficits that could not be explained by confounding factors; increasing cadmium urine concentrations being associated with increasing loss of visual function and concentration, problems with balance, and peripheral neuropathy (damage to peripheral nerves with symptoms of tingling, numbness, muscle weakness etc).35 Finally, cadmium causes thyroid hormone deficiency by interfering with the function of an important enzymes required for their synthesis; it is thought this is the result of ree radical production and lipid peroxidation by the metal as the antioxidant vitamin C reverses most of the effects.36
Sources of Aluminium
Food - Some foods such as tea and ceral crops contain naturally occurring aluminium but the greater proportion of aluminium in food comes from additives. Many food additives approved for use in the US and Europe contain aluminium and these are ubiquitous in processed foods. For example, sodium aluminium phosphate is a common raising agent in baked goods, while processed cheese is also high in aluminium.37
Food Packaging - Studies have also shown processed foods and soft drinks packaged in aluminium cans, trays and wrappers can be contaminated with considerable amounts of aluminium; this is especially true of acidic and salty foods e.g. tomato pasta sauce.38
Cookware - Just as aluminium can leach out of food packaging, cookware made of aluminium can also contaminate food. Again, acidic and salty foods are likely to be the biggest problem. The same goes for foods stored wrapped in aluminium foil.
Water - According to the world health organization (WHO) aluminium constitutes about 8% of the Earth's crust, maing it the most abundant metal on the planet. salts of aluminium are widely used in water treatment plants to reduce organic matter, turbidity and microorganism levels - "Such use may lead to increased concentrations of aluminium in finished water (i.e. municipal water supply)."39 Despite this only an estimated 5% of oral aluminium consumption comes from water - the sources just discussed being much more significant.
Air Pollution - Aluminium is a widely used metal in manufacturing industries so air pollution from aluminium plants is substantial. One study found people living close to such a plant were more than 4 times more likely to be admitted to hospital and have increased risk of suffering aluminium related health effects than those living far from such sources industrial pollution.40
Personal Care Products - Salts of aluminium such as aluminium chloride and aluminium-zirconium compounds are widely used in deodorants and antiperspirants. Research suggests that long-term use of such products can significantly increase the body burden of this toxic metal.41
Medicines - Aluminium compounds are commonly found in mdecines, either as the active ingredient, or as additives used for various reasons. An example of aluminium-containing medicines are antacids which use aluminium hydroxide as the active ingredient.
Health Effects of Aluminium
Aluminium is a potent neurotoxin. It may contribute to poor memory and concentration and mood disorders such as depression and anxiety by interfering with communication between brain cells.42 Higher aluminium levels are linked with increased production of beta-amyloid proteins and increased risk of Alzheimers disease.43 Studies show that aluminium is detrimental to bone health. A review of the medical literature found that high use of aluminium-containing antacids is often a cause of osteomalacia (softening of the bones) and fractures, even in the relatively young (40-50 age group).44 Aluminium is known to be genotoxic - it damages genetic material. It has been strongly linked to breast cancer (especially from antiperspirants) due both to the damage it exerts on DNA and because it interferes with the function of oestrogen. 45 Aluminium also interferes with key energy producing reactions within every cell and thus can be a significant contributor to symptoms of chronic fatigue and general malaise.46
Other Toxic Metals
Besides those discussed above there are a number of other toxic metals that people are may be exposed to and can have consequences for health. Among these are arsenic, beryllium, and nickel. For more information see The United States Department of Labor Occupational Safety and Health Administration's Toxic Metals webpages.
Testing for Toxic Metals
Hair Mineral Analysis
Hair mineral analysis is a cheap and easily performed way of assessing levels of toxic metals in the body. All that is required is a sample of hair which the lab then analyzes to determine the concentrations of various toxic metals it contains. The levels found in the hair are purported to give a fair estimation of those in the body as a whole. Controversy does exist over the accuracy of such tests however. One study found hair mineral analysis was an inaccurate technique for measuring nutrient minerals (e.g. magnesium, calcium) but was more helpful for detecting exposure to toxic metals.47 As discussed, toxic metals are neurotoxic; research has often linked hair levels to fatigue and mood/behavioural problems.48 Hair testing has been found to be more accurate for some toxic metals than others; mercury levels detected being more representative of the mercury distributed throughout the body than those of aluminium.49 It must also be kept in mind that hair samples may be contaminated by external sources such as air pollution and cosmetic hair products. There also exist doubts due to different techniques used by laboratories and variability in results from different laboratories.50 Hair mineral analysis is therefore best used as an initial screen for toxic metals; more accurate methods can confirm concerning results.
Other Forms of Testing
To confirm metal toxicity suggested by inexpensive hair mineral testing urine levels are often tested after the patient is given a chelating agent (a substance that binds toxic metals and carries them out of the body) such as DMSA. This can give an accurate result if carried out by a skilled lab technician using the latest equipment; many expert environmental medicine doctors now recommend testing of a whole blood sample however as analytical technology is now very accurate.51
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