Mercury exposure has long been known to cause neurological problems. Recently, research shows that mercury accumulates at higher levels in the brain than in other parts of the body.
Mercury (Hg) in all forms is hazardous to all living things. Here I’ll explain the physiological effects of mercury and how the body eliminates it. Genetic variants play a role in how quickly you excrete mercury; diet and lifestyle factors are also important. I’ll wrap up this article with an overview of the research on different natural supplements that impact mercury detoxification.
Mercury: Effects and Detoxification
Mercury is the only metal that is a liquid at normal temperatures and pressures. It is classified as a heavy metal (along with lead, cadmium, iron, zinc, etc.), and it can be toxic in the body even at very low levels.
Mercury can build up in the body, causing negative health effects on the central nervous system and the kidneys. It is a fancy way of saying that it hurts the brain, causing fatigue, memory impairments, nervousness, insomnia, and tremor. Exposure to a lot of mercury at once can cause nausea, vomiting, kidney damage, bloody diarrhea, and even death.[ref]
We are exposed to mercury through a variety of pathways:
- Fish and seafood contaminated with mercury are the most significant sources of mercury for many people.
- Dental amalgam (silver fillings) can break down and possibly cause mercury to enter your system.
- Certain vaccines contain trace amounts of mercury (thimerosal) as a preservative.
- Occupational exposure can happen either through breathing in mercury-contaminated air or via skin exposure. Industries that use mercury include chemical labs, gold mining, battery makers, dentists and amalgam makers, insecticide manufacturing, and CFL bulb manufacturing.
Air pollution containing mercury can also be a problem in some areas. Elemental mercury can be a contaminant in air pollution, and it also can be inhaled when near liquid mercury. Liquid mercury (such as in CFL bulbs or thermometers) easily vaporizes and is absorbed in the lungs. Mercury can also be absorbed through the skin.
Forms of mercury:
All forms of mercury can be a problem, depending on the concentration. When it comes to detoxifying mercury, though, the different forms of mercury use different detox pathways.
Mercury can be classified as:
- Organic mercury: mainly methylmercury, which is the form found in seafood
- Inorganic mercury: elemental mercury in air pollution (fossil fuel emissions), evaporation from liquid mercury, mercuric salts dissolved in water
Organic mercury is formed from inorganic, airborne mercury, such as from fossil fuel emissions entering bodies of water. In aquatic sediments, certain bacteria convert mercury into methylmercury. Extremely toxic, methylmercury can be easily absorbed via drinking water or eating fish that have absorbed the methylmercury.
Dental amalgams – silver fillings – are another source of exposure to inorganic mercury. To add to the complexity, some forms of mercury convert in vivo from inorganic to organic.
Why is mercury toxic?
While mercury toxicity can affect someone at any age, it is especially devastating to a developing fetus. Exposure to low levels of mercury can affect brain formation by killing off the neuronal stem cells that form the brain.
Mercury also affects children and adult brains, just not at the devastating level seen in developing babies. Neurogenesis, or the formation of new neurons, happens at low levels throughout life. Research shows that mercury inhibits the development of astrocytes from neuronal progenitor cells. Instead, there is a shift in cell type from astrocyte formation to more glial cells. While both cell types are important, we need them in the right amount. Essentially, methylmercury is thought to disrupt some of the cell signaling taking place when neurons are forming.[ref]
The term “Mad as a hatter” referred to the neurological changes from long-term mercury exposure. In England, the process of making felt hats used to include using mercury to stabilize the wool. Hat makers often ended up with mercury poisoning symptoms that caused memory loss and personality changes.
Mercury is stored in the brain at a higher level than the rest of the body. Some studies show that the brain stores mercury at 3 to 6 times the rate of the rest of the body.[ref]
Recent research points to a potentially significant way that mercury causes toxicity. Studies now show that mercury can take the place of selenium in specific proteins, causing those proteins not to function. The selenoproteins that are targeted include thioredoxin reductase 1 and 2. These are major antioxidant and redox regulating enzymes.[ref]
How long does mercury stay in the body?
When inhaled, organic mercury has a half-life of around 60 days in the body. But mercury in the brain can stay there for 20 years or more.[ref]
It takes time for the symptoms of mercury toxicity to show up. Research shows that it can take up to 5 months for some symptoms to appear.[ref]
How is mercury detoxified and excreted?
Mercury is eliminated primarily by glutathione detoxification. It is excreted in bile, feces, or urine. The glutathione-S-transferase enzymes are essential in making mercury soluble in a form that can be excreted from the body.[ref]
Glutathione is synthesized from l-glutamate and cysteine, with glycine also needed for the second step of biosynthesis. All animal cells can synthesize glutathione, and it is an essential antioxidant and detoxification compound.
With the help of enzymes to catalyze the reaction, glutathione is bound to methylmercury (the kind found in fish) for excretion. There are a couple of other routes of detoxification of mercury also. For elemental mercury, free cysteine is also utilized for detoxification. Metallothioneins are cysteine-rich proteins that can bind with mercury for excretion in certain circumstances.[ref]
We want mercury to be excreted as quickly as possible so that it doesn’t hang around and end up in the brain. This detoxification pathway brings us to the genetic variants that impact how well your body excretes mercury.
Genetic variants related to mercury detoxification:
GST family of enzymes:
The glutathione-S-transferase family of enzymes is important in detoxification. Researchers have identified at least 16 different GST genes, and the redundancy of this gene family shows how important they are to us and our ancestors.[ref] The enzymes are used in reactions to conjugate glutathione to hydrophobic compounds. The addition of glutathione makes the toxic compounds more water-soluble and thus able to be excreted in urine or feces.[ref]
GSTM1 enzyme: This enzyme helps the body detoxify several types of carcinogens, drugs, toxins, and oxidative stress byproducts. Not everyone has a functioning copy of this gene.[ref] The deletion is fairly common with 50 – 78% of people, depending on the ethnic group having the null genotype for GSTM1.
Check your genetic data for rs366631 (23andMe v4 only):
- A/A: deletion (null) GSTM1 gene. Decreased mercury detoxification, higher levels of mercury in hair and blood tests[ref][ref] (note: this is a common genotype in many population groups)
- A/G: GSTM1 present
- G/G: GSTM1 present
Members: Your genotype for rs366631 is —.
GSTP1 gene: GSTP1 is involved in estrogen metabolism as well as various toxicants including mercury.[ref]
Check your genetic data for rs1695 (23andMe v4, v5; AncestryDNA):
- A/A: typical
- A/G: typical risk
- G/G: reduced function; decreased mercury detoxification, higher mercury levels[ref][ref][ref]
Members: Your genotype for rs1695 is —.
GCLM gene: This gene encodes the glutamate-cysteine ligase enzyme, which is the rate-limiting enzyme in glutathione synthesis.
Note that not all studies seem to agree on this specific variant. I’ve gone with what the majority of studies show.
Check your genetic data for rs41303970 -588T (23andMe v4; AncestryDNA):
- G/G: typical
- A/G: Higher blood mercury levels; Decreased/slower mercury detoxification
- A/A: Higher blood mercury levels; Decreased/slower mercury detoxification[ref][ref][ref][ref]
Members: Your genotype for rs41303970 is —.
Sensitivity to deleterious effects of mercury:
CPOX4 gene: encodes coproporphyrinogen oxidase (CPOX), one of the enzymes in the formation of heme and the formation of neurotransmitters in the brain.
Check your genetic data for rs1131857 (23andMe v4, v5; AncestryDNA)
- T/T: typical
- G/T: increased sensitivity to neurobehavioral effects of mercury[ref]
- G/G: increased sensitivity to neurobehavioral effects of mercury[ref]
Members: Your genotype for rs1131857 is —.
Obviously, you want to avoid exposure to mercury at higher levels. The fact that it can remain in the brain for 20 years is disconcerting.
Which types of fish are highest in mercury?
According to the FDA, fish high in mercury include (listed higher to lower):[ref]
- king mackerel
- orange roughy
- Chilean bass
- tuna (canned, Albacore)
- white croaker
Drink tea with your fish? A recent study showed that tannic acid and EGCG, found in black or green tea, help to block mercury absorption from foods.[ref]
Testing for mercury:
Blood tests and hair metal tests are available to check for mercury. Mercury accumulates in the hair at about 250x the amount seen in the blood, on average. Hair testing accuracy depends on age, gender, and genetics. Normal levels of mercury in the hair are 1-2 ug/g. In hair testing for adults, neurological effects are seen at 50 ug/g. In blood mercury tests, people who don’t eat fish usually have levels below 2ug/L, while individuals who consume a lot of contaminated fish may range from 5 to 10ug/L.[ref]
Supplements that may help with mercury detoxification:
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Debbie Moon is the founder of Genetic Lifehacks. Fascinated by the connections between genes, diet, and health, her goal is to help you understand how to apply genetics to your diet and lifestyle decisions. Debbie has a BS in engineering and an MSc in biological sciences from Clemson University. Debbie combines an engineering mindset with a biological systems approach to help you understand how genetic differences impact your optimal health.