Many heavy metals are naturally found in the earth and do not pose any health risks to people. In rare cases, some people may be exposed to excessive amounts of heavy metals, which is referred to as heavy metals toxicity or poisoning.
What are Heavy Metals?
Definition
Many heavy metals like mercury, lead, cadmium, and arsenic are found in the soil, water, food, and in some commonly-used household products. Most of the time, we go about our daily lives unharmed by these elements [1].
Chemically speaking, heavy metals are metals or metalloids (having properties of metals and nonmetals) that have a density of at least 5 g/cm3 and adversely affect the environment and living organisms if present in large quantities [2].
Iron, copper, chromium, and zinc are also sometimes classified as heavy metals. These minerals are required by humans in trace amounts [3].
Poisoning
Heavy metal poisoning is extremely rare in the United States. It happens only when people are exposed to exceptionally high amounts of heavy metals in their environment, typically due to work-related conditions.
Factories and large-scale farms using pesticides in some parts of the world may expose workers to excessive amounts of certain heavy metals [1].
Despite this, various heavy metals tests and “detox” protocols are being promoted online as healthy for the general population or for people suffering from certain health issues. Science goes against these approaches. Evidence suggests that people should be cautious about these unproven, potentially unsafe, and often costly treatments.
Additionally, detox supplements have not been approved by the FDA for medical use. Supplements generally lack solid clinical research. Regulations set manufacturing standards for them but don’t guarantee that they’re safe or effective. Speak with your doctor before supplementing.
The FDA also clearly advises consumers against using over-the-counter chelation agents, which can be dangerous. Chelation agents should only be used by prescription and for certain cases, under medical supervision [4].
List
Some heavy metals play no beneficial role in the body and, instead, interfere with normal body processes in excess [2]. These include:
- Arsenic
- Mercury
- Cadmium
- Lead
Other metals are vitally important to health in small quantities, however, may become toxic in excess [2]:
Heavy metals are everywhere around us and originate from both natural and human sources, such as volcanic eruption, coal burning, and gold mining [5].
According to some estimates, in recent years, the amount of heavy metals in the environment has increased significantly. Scientists say this necessitates strategies to decrease exposure to heavy metals and identify substances that are driving pollution. The goal is to find ways to reduce and overcome their harmful effects on all living beings [5].
Heavy Metals Testing
Who is at risk?
Heavy metal poisoning is extremely rare in the US. The following factors increase the risk of heavy metal poisoning [1]:
- Exposure to chemicals such as insecticides, herbicides, fungicides, algicides, sheep dips, wood preservatives, and dye-stuff on farms (arsenic)
- Living in some parts of the world that have higher levels of heavy metals in the soil of water (West Bengal, Bangladesh, Thailand, Inner Mongolia, Taiwan, China, Mexico, Argentina, Chile, Finland, and Hungary) (arsenic)
- Cigarette smoke (cadmium)
- Working in the mining or smelting industry (cadmium) or in large factories (chromium)
- Working on manufacturing batteries, pigments, stabilizers, and alloys (cadmium)
- Construction work with cement (chromium)
- Working on manufacturing lead-acid batteries, ammunition, and metal products (lead)
- Exposure to deteriorating household paints
- Working in the electrical industry (switches, thermostats, batteries) (mercury)
- Possibly dental amalgams (mercury)
- Eating fish caught in high-mercury areas
- Taking herbal supplements contaminated with heavy metals (often from China or India)
Physicians will not test people who are not at risk of heavy metals toxicity – these tests aren’t routine.
Your doctor will first ask you about your job, lifestyle, diet, and any other factors that may have put you in contact with harmful compounds.
Various types of tests exist. They may require urine, blood, or less commonly hair or nail samples. Some require an X-ray or other imaging procedures [6].
Doctors will usually order a test if a patient shows symptoms and has a history of exposure.
Blood Tests
In most cases, blood testing is indicative of acute exposure rather than the total body burden (total amount of heavy metals accrued over one’s lifetime that is present in the body). However, there are exceptions [7].
Urine Tests
24-h urine testing may be used to assess mercury, arsenic, lead, and cadmium exposure in some cases.
Scientists suggest that urine tests may give an inaccurate representation of body burden for some metals, as they are often present in different forms, stored in different areas and processed by and excreted by the body differently [7].
For example, mercury is present in the body in two forms: organic (methylmercury or dimethylmercury) and inorganic (mercury salts, such as mercury chloride). Organic is largely excreted through the bile and feces, while inorganic is eliminated via the urine [7].
Therefore, whole blood is the preferred test for organic mercury body burden and urine testing may have advantages for measuring the body burden of inorganic mercury [7].
Additionally, urine tests became controversial since companies started offering “at home heavy metals tests.” No evidence backs up heavy metals testing in most people and at-home testing may lead to improper sample collection, inaccurate results, and questionable interpretation.
The Heavy Metals Challenge Test
A highly controversial, unproven, and likely dangerous type of test is called the “challenge test” or “provoked urine test.” It involves using large doses of a strong prescription chelating agent, usually dimercaptosuccinic acid (DMSA). Advocates claim this draws metals out of the body and into the urine where they can be analyzed [6].
This practice is likely dangerous and there is no valid evidence to support it.
DMSA is contained in an FDA-approved prescription product indicated for the treatment of lead poisoning in children [4].
The FDA recently warned consumers not to use Captomer or Captomer-250 by Thorne Research, which contained DMSA. Thorne subsequently recalled this product, which was being marketed as a dietary supplement for heavy metal toxicity and heavy metal chelation therapy [4].
The FDA advised consumers to avoid all products offered over-the-counter (OTC) for chelation or detoxification. There are no FDA-approved OTC chelation products.
Procedures involving chelation agents carry major health risks and should be performed only under medical supervision. FDA-approved chelating agents are available by prescription only and are approved for use in specific indications [4].
Chelation is the process of binding heavy metals with certain drugs to facilitate excreting them from the body [6].
Chelation challenge tests are associated with many adverse reactions. Some claim that this is because the influx of mobilized metals can overwhelm the body’s detoxification pathways and redistribute metals to other tissues [8].
Other criticisms of challenge testing include false positives, which may lead to inappropriate, ineffective, potentially dangerous therapies. Additionally, this test lacks a standard of protocol and laboratory reference ranges to interpret the results [9, 10].
Several cases of people who were healthy and symptoms free but told that they suffer from “hidden heavy metal toxicity” have been reported. When these healthy people were given DMSA, the urinary mercury levels seem to rise, and they were diagnosed with mercury toxicity. This can lead to serious side effects and misleading diagnostic advice [11].
Therefore, medical experts and government organizations strongly recommend against the “challenge testing” [12].
Despite the dangers and lack of evidence, the test is still used by some practitioners. They argue that the test allows them to determine the most effective chelating agent and to detect an absorption or tolerance problems with the agent. Their claims are not evidence-based and the whole procedure can be deceptive to patients [6].
Hair Testing
Hair and nail testing mainly reflects past exposure. Hair analysis is usually only used in forensics, for research purposes, or rarely in people with chronic exposure and unspecific symptoms. Nail testing is even less common. These methods are, overall, unreliable and inaccurate compared to blood and 24-h urine tests [13, 14, 15].
Experts point out that improper hair testing paired with unproven diagnostic markers (like the challenge test mentioned above) can lead some patients to believe they have poisoning even if they were not exposed to heavy metals. Chelation side effects and misleading advice from “detox” experts contributes to the confusion and worry many patients face [16].
Heavy Metals Toxicity Symptoms
A General Overview
Symptoms of heavy metal intoxication depend on the metal and level and duration of exposure.
Broadly speaking, symptoms may include:
- Forgetfulness or confusion [17]
- Insomnia and mood change [17]
- Vision abnormalities [17]
- Headaches [1]
- Muscle and joint pain [1]
- Constipation [1]
Limited studies have associated poisoning with certain heavy metals with intellectual disability in children and kidney and liver diseases [17]
Arsenic and cadmium are classified as known carcinogens (causes cancer). Lead and mercury are possible carcinogens as well [6].
One large observational study in 1578 healthy women found that high levels of lead and cadmium in the placenta may affect the growth and development of the fetus. Lead was found in all cord blood and 96% of placental tissue, while cadmium was found in 95% of cord and 98% of maternal blood samples [18].
Basic science suggests that excess heavy metals bind proteins and prevent their functioning to disrupt cellular function by interfering with minerals like magnesium and causing oxidative stress [5].
Scientists are investigating the combined effects of various heavy metals on worms [19].
The vast majority of research on heavy metals focused on the 4 metals described below. They are estimated to be present in disproportionately higher levels in the environment than other heavy metals. Studies suggest that they also have the greatest likelihood to produce health issues in excess [1].
Mercury
According to some studies, mercury is considered to be the most toxic heavy metal in the environment [2].
A major source of chronic, low-level mercury exposure is seafood, with additional sources including occupational exposure such as small-scale gold mining and dental amalgams [20].
Mercury accumulates in organisms as you go up the food chain, meaning larger fish such as tuna, shark, and swordfish have proportionally more mercury than smaller fish like sardines, mackerel, and anchovies [7].
Because it’s attracted to fat (lipophilic), this metal may accumulate in the fat and liver of fish. When consumed in excess by humans, it can accrue in the brain and nerves (specifically the myelin sheaths of nerves, which are made of fats) [1]. The brain, kidneys, and liver are the major storage sites for mercury accumulation.
Limited and preliminary studies have associated mercury poisoning with::
- Depression [2]
- Memory problems [2]
- Fatigue, headache [2]
- Increased blood pressure and heart rate [2, 21]
- Heart disease [22]
- Hair loss [2]
- Permanent brain damage [23
- Kidney damage [23]
- Loss of balance and coordination [24]
Chronic mercury exposure has been associated with heart attacks and Alzheimer’s-like brain changes in lab animals [25, 26].
Some scientists in Taiwan have suggested a link between chronic mercury exposure and Alzheimer’s Disease, but this association is controversial and unverified. In this study, dental amalgams were associated with an increased risk for Alzheimer’s disease in women [27]
According to another study, mercury levels range from 2 – 10 times higher in individuals with dental amalgams [26].
Further research should clarify the link between Alzheimer’s disease and mercury exposure.
Why It’s Harmful
Researchers think that mercury increases the formation of reactive oxygen species, both directly by being a pro-oxidant and indirectly by depleting antioxidants like glutathione, which may lead to an increase in oxidative damage to DNA, lipids, and proteins [24].
Mercury can also bind to amino acids and enzymes like glutathione, cysteine, and sodium-potassium adenosine triphosphatase, which may disrupt cellular function [28, 2].
Studies show that the neurotoxic effects of mercury may be due to its ability to increase levels of glutamate in brain cells, which may cause damage and neuronal death [29, 24].
Arsenic
Arsenic is detected at low concentrations in virtually all environments. Aside from volcanic eruptions and soil erosion, people can also be exposed to arsenic if they come into contact with certain insecticides, herbicides, fungicides, algicides, sheep dips, wood preservatives, and dye-stuffs [1].
Some parts of the world are contaminated with large amounts of arsenic. Foods grown in contaminated soil and water are the main routes of exposure for people living in these areas [30, 1].
Also, people working in glass-making, smelting, pesticide manufacturing, and semiconductor manufacturing industries may be exposed to significantly higher levels of arsenic than the general population [31].
High levels of arsenic have been reported in West Bengal, Bangladesh, Thailand, Inner Mongolia, Taiwan, China, Mexico, Argentina, Chile, Finland and Hungary [1].
In recent years, there were scandals when high levels of arsenic were found in rice and apple juice. Some European scientists recommended that babies don’t drink rice-based drinks because of this [32, 33].
The primary targets for arsenic and compounds containing arsenic are the kidneys and the liver because they are generally processed by the liver and excreted in the urine [34, 30].
Excessive chronic exposure during childhood has been associated with behavioral dysfunction during puberty, possibly lasting into adulthood [35].
Arsenic exposure has also been associated with:
- Deficits in verbal intelligence long-term memory in children [36]
- Diabetes [37]
- Increased fetal mortality and preterm birth [38]
Long-term exposure has been linked with:
- Inflammation of the nerves, causing pain and loss of function [39]
- Skin lesions, darkening of the skin (hyperpigmentation) [30]
- Internal cancers including bladder, kidney, liver prostate, and lung [40]
- High blood pressure [2]
- Increased risk of mortality [41]
- Toxic effects on genes, which can cause mutations [33]
Scientists think that arsenic exerts its toxic effect by inhibiting enzymes in the mitochondria, replacing phosphorus in various biochemical reactions, depleting thiamine (vitamin B1), and causing oxidative stress through depletion of enzymes like glutathione and superoxide dismutase (SOD) [34].
Lead
Up until recent years, lead was often used in paints, ceramics, and pipes. Although its use in these products has been significantly reduced, one report from 2002 suggested that between 2% and 25% of painted building parts in the US were coated with lead-based paint [42].
This study estimated the greatest risk in older houses with lead-based paint hazards that are occupied by families with children under 6 years of age, especially if they are also doing renovation that disturbs lead-based paint [42].
The majority of lead poisoning cases in adults are due to occupational exposure, such as inhaling lead-contaminated dust, while lead exposure in the general population is mainly through food [43].
Studies show that lead can accumulate in the kidneys, liver, heart, brain, and especially in the bones [42].
Symptoms of lead exposure on the brain may include:
These symptoms are nonspecific and overlap with many other conditions.
Lead exposure is of particular concern in pregnant women, as it easily crosses the placental barrier and enters the developing fetus. Both human and animal studies show that lead exposure during pregnancy is associated with reduced birth weight and preterm delivery, as well as cognitive deficits in the offspring [44, 45, 46].
The main mechanism by which scientists suspect lead exerts toxic effects is through its ability to block the actions of calcium and disrupt the activity of various enzymes and proteins, including glutathione and superoxide dismutase, and causing oxidative stress [47].
Cadmium
Cadmium is a relatively water-soluble metal. In smokers, tobacco is the main source of cadmium because tobacco plants tend to accumulate the metal from the soil [31].
For non-smokers, the main source is through diet and occupational exposure, including metal industries, soldering, battery manufacturing, and cadmium-contaminated workplaces [48].
Cadmium is highly toxic to the kidneys and preferentially accumulates in a specific type of cell (proximal tubular cells) [2].
Long-term exposure may cause:
Mechanism of Toxicity
Although the mechanisms of cadmium toxicity are not fully understood, research suggests it causes oxidative damage indirectly by decreasing antioxidants, rather than directly creating free radicals like the other metals discussed [49].
Cadmium also tends to bind to key enzymes and proteins, preventing them from functioning normally [48].
Cadmium toxicity tends to disrupt calcium balance, in which the kidney plays a large role in regulating [48].
Takeaway
Many symptoms of heavy metal poisoning are unspecific. Remember that poisoning is uncommon in the general population.
We’re normally exposed to tiny amounts of these metals, many of which are naturally found in the earth, on a daily basis. This hasn’t been associated with any health risks.
If you think that you are at risk of chronic heavy metal poisoning, contact your doctor to get an accurate diagnosis and treatment. Your doctor will assess your symptoms and exposure risk. People who work in certain industrial environments might be at risk.
If you have been acutely exposed to heavy metals – such as by inhaling metal fumes in the workplace or elsewhere – urgently contact a poison center near you (call 1-800-222-1222).
In case you are not are risk of poisoning, we highly advise against doing unproven and potentially dangerous tests like the challenge test.
We also advise against the unapproved use of chelation agents, which can cause serious side effects.
Plus, keep in mind that supplements marketed for “detoxing” heavy metals have not been approved for medical use. There’s no evidence to support their use. If they don’t contain chelating agents, they might be safe. But they are likely to be expensive and ineffective.
