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From the Townsend Letter
January 2017

Mercury: The Quintessential Anti-Nutrient
by Sara Russell, PhD, NTP, and Kristin G. Homme, PE(ret.), MPP, MPH
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  • The chronic effects of cumulative, low-dose mercury exposure are underrecognized by both mainstream and alternative health authorities and, consequently, by the public. Mercury can cause or contribute to most chronic illnesses, including neurological disorders, cardiovascular disease, metabolic syndrome, chronic fatigue, fibromyalgia, adrenal and thyroid problems, autoimmunity, digestive disorders, allergies, chemical sensitivities, mental illness, sleep disorders, and chronic infections such as Lyme and Candida. Mercury toxicity should be suspected in individuals experiencing multiple health problems.
  • Diagnosis of chronic mercury toxicity is often difficult because the body's natural defenses may mask or delay symptoms. Natural defenses are a function of genetic susceptibility, epigenetic factors, micronutrient status, and allostatic load (cumulative wear and tear on the body). Furthermore, individuals who retain mercury may counterintuitively show low levels in blood, urine, and hair.
  • The developmental window from conception through early childhood is one of extreme vulnerability to mercury. Mercury is an epigenetic toxicant (affecting future gene expression) as well as a neurotoxicant. Damage may be permanent; therefore, prevention is key.
  • For most people mercury is the most significant toxicant in the body. By promoting oxidative stress and depleting antioxidant defenses, including the glutathione system, mercury impairs the body's response to toxicants in general including mercury itself.
  • Mercury toxicity creates a need for extra nutrition, both to repair damage and to provide ample enzyme cofactors that can push blocked enzymes. Carbohydrate intolerance can be a symptom of mercury toxicity, and fat can be a preferred fuel. Many people with chronic mercury toxicity have found a nutrient-dense diet to be a useful starting point for symptom relief. Individualized supplementation may also be helpful to overcome the extreme nutritional depletion and unnatural toxic state.

Mercury is an unusually insidious toxicant that can cause or contribute to most chronic illnesses. Its effects on various body systems can be mutually reinforcing, setting up a complex process of damage and dysfunction. For example, by inhibiting the glutathione system, which is key to detoxification, mercury perpetuates a vicious cycle of susceptibility and toxicity. As a result, mercury promotes nutritional depletion, oxidative stress, hormonal disruption, immune alteration, and neurotransmitter disturbances, which in turn can cause poor digestion, leaky gut, food allergies, altered gut flora, and autoimmunity. Yet, despite its pervasive ability to damage the body, mercury easily eludes detection; and many affected individuals have no idea that their unexplained health problems are due to past or ongoing mercury exposures.
Adding to the confusion, symptoms may manifest differently in each person depending on exposures, lifestyle, genetics, and micronutrient status. For example, it may manifest in one person as autoimmune issues such as Hashimoto's thyroiditis, multiple sclerosis, or systemic lupus erythematosus and in someone else as mood, behavior, learning, or psychiatric problems. Long latencies may occur with onset of symptoms sometimes occurring months or years after the exposure has ceased.1,2 Many symptoms are vague, resembling premature cellular aging. Other symptoms are more distinct, a case in point being erethism (a constellation of personality traits including timidity, diffidence, contentiousness, insecurity, bluntness, rigidity, excitability, and hypersensitivity to criticism and to sensory stimulation).3-5 The term erethism, or reddening, derives from the person's tendency to blush.6 Considering the subtle but reproducible effects of mercury on emotions, a number of problems that are blamed on character, personality, and stress may in fact be caused or compounded by low-level mercury toxicity.
MetalPulUnfortunately, the public receives mixed messages from health authorities and agencies about the risks of mercury from routine exposures involving dentistry, fish, and vaccines. Certain exposure risks are widely discounted by the mainstream; yet according to the US Environmental Protection Agency, approximately 2–7% of women of childbearing age in the US have blood mercury levels of concern.7 And there is reason to believe that these regulatory levels of concern are too lax.i,8 In fact, neurodevelopmental disorders affect almost 11% of all US births, up 30% over the past decade;9 and subclinical decrements in brain function are even more common, affecting up to 15% of births.10 However, health authorities are unlikely to provide useful guidance on mercury risks for several reasons. Mercury is technically and politically difficult to study; thus, scientific conclusions about risks remain couched in uncertainty. Mercury's effects are non-specific and multi-factorial. Finally, much exposure is iatrogenic  –  caused by health care  –  making it an unpopular topic.

For most people, the major sources of mercury exposure are elemental mercury vapor from dental amalgams and methylmercury from dietary fish. Ethylmercury in certain vaccines provides smaller amounts, but these can be highly toxic during the vulnerable window of gestation and early childhood. These three forms of mercury are all easily absorbed and readily distributed throughout the body. Being lipophilic, these forms of mercury leave the bloodstream quickly, passing through biological membranes and concentrating in cells (including brain cells).11 Mercury is especially drawn to high-sulfur organelles such as mitochondria. Once inside a cell, mercury is soon oxidized to Hg2+. This is a hydrophilic (lipophobic) form of mercury and therefore cannot easily pass through biological membranes. This form of mercury thus becomes trapped inside the cells, causing ongoing damage.12 Mercury has a particular affinity for the brain, where it may be retained indefinitely.13,14 It also accumulates in epithelial tissues, organs, and glands such as the salivary glands, thyroid, liver, pancreas, testicles, prostate, sweat glands, and kidneys as well as the epithelium of the intestinal tract and skin.15

Table I: Common Exposures to Mercury
Dental amalgams – a few micrograms of mercury vapor per filling per day.
Dietary fish – depending on species, a portion may contain roughly 1–100 micrograms of methylmercury.
Certain vaccines – 12.5 to 25 micrograms of ethylmercury per shot.
Prenatal exposures – levels are unknown but clinically significant.

Dental Amalgam
Dental amalgam, the material used in "silver fillings" beginning in the nineteenth century, is about 50% mercury. Mercury is highly volatile; consequently, amalgams continuously off-gas in the mouth. Health authorities have deemed amalgam as safe based on studies that were designed to detect only obvious harm, not subtle or long-term effects. New evidence indicates that susceptibility (and resistance) to mercury toxicity is driven by genes, only a few of which have been identified.16 Furthermore, evidence indicates that exposure from amalgams is sufficient to cause harm to susceptible people.17 The authors of the mercury chapter in the most recent metals toxicology textbook estimate that roughly 1% of the population is incurring clinical illness from their dental amalgams  –  and this is likely to be a gross underestimate because it excludes cases that have another diagnosis such as multiple sclerosis that may have a mercury component.18
The World Health Organization estimates that the typical absorbed dose of mercury from amalgams is 1–22 micrograms per day with most values in the range of 1–5 micrograms per day.19 Various factors including gum chewing and bruxism can increase these exposures to an upper range of about 100 micrograms per day.20 Preliminary evidence suggests that certain types of electromagnetic radiation including from mobile phones and from magnetic resonance imaging (MRI) may increase the release of mercury vapor from dental amalgams.21
In 2009, the US Food and Drug Administration (FDA) reiterated the safety of dental amalgam despite much scientific evidence to the contrary. As of 2016, public interest groups are challenging this "final amalgam rule" in federal court. Issues to be litigated include whether amalgam is deemed an implant, which would require manufacturers to provide proof of safety, and whether the toxicity warnings that are given to dentists via labeling requirements should also be given to patients. Norway, Denmark, and Sweden have banned dental amalgam; and, as of May 2015, a scientific committee of the European Commission recommends that non-mercury alternatives be used in fillings for pregnant women and children.22
As if the cumulative effects of ongoing amalgam exposure were not enough, unsafe amalgam removal can cause acute exposures to mercury vapor. Thus, patients wishing to replace amalgam fillings with less toxic alternatives must evaluate dentists' use of adequate protective measures. The International Academy of Oral Medicine and Toxicology (IAOMT), a professional dental organization, has developed a protocol and training program that attempts to minimize the exposure to mercury vapor to the patient, dentist, and staff during amalgam removal. In women of childbearing age, removal of amalgam should be timed to avoid the 12–18 months preceding conception as a well as pregnancy and breastfeeding.

Dietary Fish
Mercury released into the atmosphere through natural and human activities is deposited in soil and water where it enters the food chain. Mercury accumulates in fish, particularly large, long-lived ocean fish. Natural releases from the Earth's crust and the oceans account for 60–70% of the annual releases of mercury to the atmosphere. The remaining 30–40% is attributable to human activities.23 Thus, humans have always encountered some mercury in certain fish; and, as long as the natural defense systems are working, one can consume mercury-containing fish in moderation. In healthy individuals, intestinal metallothioneins (a class of metal-storage molecules that can be cumulatively damaged by mercury) can sequester ingested mercury and slowly allow its excretion. Selenium, discussed below, is a micronutrient that offers some protection against mercury and is found in fish as well as other foods.
Mercury levels in fish vary widely by species and by individual, ranging from less than 0.1 part per million (ppm) for salmon and sardines to more than 1 ppm for some samples of tilefish, shark, swordfish, and king mackerel. This means that a typical 3.5-ounce (100 gram) serving of fish could contain anywhere from a few micrograms to more than 100 micrograms of mercury. Tuna contains moderate levels, which vary by species. The FDA sets an Action Level for mercury contamination in commercial fish of 1.0 ppm; this means that federal officials are allowed to confiscate the product but not that they actually do so.

One of the most controversial aspects surrounding vaccines is their mercury content. Prior to about 2004, many childhood vaccines contained thimerosal, a preservative and adjuvant that is 50% ethylmercury.ii Childhood exposure to thimerosal rose sharply in the US during the 1990s as new vaccines were added to the childhood vaccine schedule set by the US Centers for Disease Control and Prevention (CDC). Infants subjected to the CDC vaccine schedule during this time typically received up to 187.5 micrograms of mercury in the first six months of life.24
No regulatory safety standard exists for ethylmercury. Because ethylmercury is chemically similar to methylmercury, the above-mentioned 187.5-microgram dose can be compared to the safe reference dose for methylmercury (the form present in dietary fish) set by the US Environmental Protection Agency (EPA) of 0.1 microgram per kilogram of body weight per day for chronic exposure, equivalent to about 0.3 micrograms per day for a newborn, and 0.6 micrograms per day for a 6-month old baby. Even if the 187.5-microgram exposure, delivered in a number of concentrated doses, is averaged over the six-month period, the resulting dose of 1.04 micrograms per day is still significantly higher than the EPA's safe reference dose of 0.3–0.6 micrograms total per day for methylmercury. In addition, the EPA safe reference dose for methylmercury may be too lax,25,26 especially when applied to ethylmercury. Indeed, there may be no threshold that precludes adverse neuropsychological effects in children,27,28 whose brains are rapidly developing. Furthermore, unlike methylmercury from ingested fish, injected ethylmercury is not subject to the natural defense mechanisms related to ingestion, including metallothioneins and selenium, discussed later.
In 1999, the US Public Health Service called for the elimination of thimerosal from childhood vaccines. Nonetheless, due to supply and demand issues, it took several years to transition to reduced-thimerosal and then thimerosal-free alternatives.29
Additionally, during the period in which thimerosal began to be phased out of pediatric vaccines, the thimerosal-containing influenza vaccine became an important exposure source for fetuses and children. In 2002, the CDC began recommending that the influenza vaccine be given to children aged 6-23 months, as well as pregnant women in their second and third trimester, even though the only vaccine approved for these groups at the time was preserved with thimerosal.30 Furthermore, the CDC aggressively increased the dosing and expanded the target groups for the influenza vaccine, recommending a double dose for infants at both 6 and 7 months plus subsequent annual doses and a dose for all pregnant women, no longer limited as they previously had been to the second and third trimester.31 As of 2013, more than half of influenza vaccines were still preserved with thimerosal,32 with the availability of non-thimerosal versions subject to supply-and-demand dynamics. For example, the thimerosal-free flu vaccine shortage during the 2015 flu season led California's governor to sign an exception allowing thimerosal-containing vaccines to be administered to infants and children despite a previous statewide restriction.
Some multi-dose meningococcal meningitis vaccines and tetanus toxoid (booster) vaccines (not recommended for children under six years of age), like the multi-dose influenza vaccines, also contain thimerosal as a preservative in amounts ranging from 12.5 to 25 micrograms per dose.33 As of 2016, some childhood vaccine preparations still utilize thimerosal. In these vaccines, such as the multi-dose DTaP and the DTaP/Hib combination vaccines, most of the thimerosal is then filtered out, reducing thimerosal to "trace" amounts, according to the CDC.34

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