Mercury and Your Body: The Choices That Affect Exposure

"How big is the fish?" I asked. 

We were in Hawaii at a modestly classy restaurant and Monchong was the fish of the day. 

Attempting to clarify, I asked the young waiter a different question.

“Does it look like it would weigh over 2 kilos?”

He stammered, clearly thrown. “Uh… it’s just a fillet. Pan-fried. Probably 7 ounces?” 

I glanced at my dinner companion, who was now half-bemused, half-hiding behind the wine menu. I was asking about the size of the whole fish, not the portion on the plate.

Why? Generally the bigger the fish, the higher the mercury content, and I was always watching mine.

Our bodies rely on an inbuilt, sophisticated detoxification system which is led by our liver, kidneys, gut, lungs and skin. But even the most efficient system can be challenged by excessive exposure to certain toxins, including mercury, which we will take a closer look at today.

Among the heavy metals, mercury is one of the most clinically important and common sources of chronic exposure worldwide, which largely stems from the consumption of seafood. Mercury poisoning from dental fillings, skincare products, industrial exposure and accidental household exposure is also possible, although this is rare.  

Fish and mercury

Understanding your risk

High-risk fish: Large and/or long living fish are prone to higher mercury levels as they tend to consume smaller fish and/or have had longer for the mercury to accumulate in their muscle tissue. This mercury content is unaffected by trimming or cooking and thus, paying attention to what fish you eat is crucial.

Lower-risk fish: Small and short-lived fish options tend to be better choices; sardines, salmon, herring, mackerel, anchovies, trout and shellfish.

Why is this important? 

Mercury exposure, particularly at elevated or prolonged levels, has the potential to affect the brain, nerves, kidneys and mood. For unborn babies and young children, the risks are even greater. Mercury can potentially disrupt antioxidant enzymes, especially glutathione peroxidase, leading to oxidative stress. 

When mercury exposure is significant, symptoms can occur, although they are non-specific and overlap with many other conditions, thus making diagnosis difficult.

Some of these include: 

Cognitive and psychological symptoms 

• Brain fog 

• Memory loss 

• Difficulty concentrating 

• Mood swings (irritability, anxiety, depression) 

• Hallucinations or paranoia (severe cases) 

• Insomnia 

• Fatigue 

Neurological symptoms 

• Tremors (hands, fingers) 

• Tingling or numbness (hands, feet, face) 

• Muscle weakness 

• Poor coordination / unsteady gait (ataxia) 

• Slurred speech 

• Decline in fine motor skills 

• Headaches 

• Tinnitus (ringing in ears) 

• Visual disturbances (blurred or tunnel vision) 

• Light-headedness 

• Generalised weakness 

Physical signs 

• Some studies have reported associations with elevated blood pressure, though findings are inconsistent 

Mercury testing What to ask your doctor 

If mercury exposure is suspected, here's what your doctor can test: 

1. Whole blood mercury or specifically methylmercury when exposure from seafood (methylmercury) is suspected. A blood level reading of >10 ug/l often suggests recent excess exposure.  

2. Mercury levels in hair can be useful to assess long-term exposure over months or years to methylmercury from fish consumption. Levels above 1-2 parts per million (ppm) may warrant clinical review in the context of an individual’s exposure history. 

3. Urine mercury (24-hour urine collection) to measure elemental or inorganic mercury when chronic low-level occupational or domestic (e.g., from amalgams, skin creams) exposure is suspected. Levels above 5 ug/l may prompt further clinical assessment depending on context. 

When your doctor orders a test to check for mercury exposure, they will note both the suspected source and the symptoms on the form to help the pathology lab select the right method and reference range. 

When and why should you test for mercury? 

Testing may be considered after discussion with a clinician if you have relevant exposure risks and compatible symptoms. 

You may: 

• Eat large fish regularly, 

• live near industrial sites with history of mercury contamination, 

• have had older mercury laden dental amalgams or known past mercury exposure, 

• and/or have unexplained fatigue, numbness, or neurological issues.

  
  

Preventing mercury overload 

Preventing mercury overload is primarily about avoiding unnecessary exposure, especially from food, domestic products and environments where mercury exist or is known to accumulate. 

1. Be smart about seafood

   Limit high-mercury fish. Based on FDA, EPA and international health guidelines, general adults should limit high-mercury fish consumption; i.e. shark, swordfish, king mackerel, bigeye tuna, orange roughy and tilefish to 1 serve, or less than 200 g per month. These fish contain approximately 0.5–1.5 ppm of mercury, while low-mercury fish typically contain levels <0.1 ppm. 

   Mercury accumulates in your body over time and is very slow and hard to clear, especially the type of mercury (methylmercury) absorbed from fish. Pregnant women, those planning pregnancy and children are generally advised in national guidelines to avoid these high-mercury fish, which can cause harm to fetal brain and nervous system development even at low exposure levels. Safer choices (which can be consumed 2–3 times/week) include salmon, snapper sardines, trout, anchovies, prawns, scallops, and other shellfish. Farmed salmon generally has less mercury than wild salmon. It is always important to discuss individual considerations with a healthcare professional. 

2. Manage dental fillings wisely

   Avoid removing mercury amalgams unless cracked or medically necessary. If you have any concerns, speak to your dentist. 

3. Avoid unregulated products

   Be wary of imported (mainly originating from Asia) or unlabelled skin-lightening creams, traditional remedies or herbal powders. Always make sure to check the ingredients when purchasing skincare or herbal products sold online. 

4. Handle mercury laden devices safely

   Properly dispose of old thermometers, fluorescent bulbs, and batteries. Avoid vacuuming spilled mercury. Professional clean-up is always recommended.  

5. Support your body’s natural detox system

   Two nutrients that have been investigated in research for their possible roles in the body’s antioxidant pathways are selenium and N-acetylcysteine (NAC). If exposure is suspected, supplement use may be considered under personalised medical supervision. 

Selenium Research into interactions with mercury 

• Selenium binds tightly to mercury, forming a stable, inert complex (Se: Hg). Some studies suggest this interaction may influence antioxidant enzyme activity though primarily gathered from experimental and observational research. 

• It restores the function of key antioxidant enzymes like glutathione peroxidase and thioredoxin reductase, which mercury tends to block. 

• It helps prevent mercury from entering the brain and supports its elimination, mostly via urine. 

Mercury depletes selenium-dependent enzymes. Replenishing selenium may support the body’s natural detox balance and antioxidant defence. Selenium has been explored for potential protective interactions in research. Clinical significance in humans remains an area of ongoing study. 

N-Acetylcysteine (NAC) Studied as a glutathione precursor 

• NAC is a precursor to glutathione, which contributes to detoxification in the human body. 

• Research has examined whether NAC influences antioxidant pathways and cellular processing of certain toxins, though clinical applications remain uncertain. 

• Studies suggest NAC may reduce oxidative stress and may have the potential to protect nerve tissue from damage caused by mercury. 

Mercury overwhelms your cellular antioxidant defences. Together, selenium and NAC have been studied for their potential to support the body’s natural detoxification process: selenium helps bind mercury, while NAC assists the body’s antioxidant defences. Both may help support your natural detox capacity, particularly in the context of low-level, long-term exposure. 

Aim to support your body by consuming a nutrient-rich diet consisting of: 

• Selenium. Dietary sources include Brazil nuts, eggs and ironically, certain seafood. Keep in mind that just 2 Brazil nuts contain 100-200 micrograms of selenium, around twice the recommend daily allowance (NHMRC, 2017). 

• Cysteine-rich foods such as garlic, onions and legumes. Cysteine is the amino acid that acts as the rate-limiting precursor to glutathione.  

• Antioxidants such as leafy greens, berries and cruciferous veggies. 

In some research contexts, investigators have explored selenium and NAC supplementation in these ranges: 

• NAC up to 1200 mg/d 

• Selenium up to 100-200 ug/d 

These figures reflect study parameters rather than clinical recommendations and use should only occur under the supervision of a qualitied health professional. 

Mercury poisoning is preventable. Being mindful of seafood choices, avoiding mercury containing products and supporting your body’s natural detox systems can aid in remaining under harmful levels. If you suspect mercury might be affecting your health, talk to your doctor. In certain clinical contexts, clinicians may consider nutritional or supportive measures alongside standard management. 

References

• Li, Y. F., Dong, Z., Chen, C., Li, B., Gao, Y., Qu, L., Wang, T., Fu, X., Zhao, Y., & Chai, Z. (2012). Organic selenium supplementation increases mercury excretion and decreases oxidative damage in long-term mercury-exposed residents from Wanshan, China. Environmental science & technology, 46(20), 11313–11318. https://doi.org/10.1021/es302241v

• National Center for Biotechnology Information. (2026). PubChem compound summary for CID 23931, mercury.

  https://pubchem.ncbi.nlm.nih.gov/compound/Mercury

• Seppänen, K., Kantola, M., Laatikainen, R., Nyyssönen, K., Valkonen, V.-P., Kaarlöpp, V., & Salonen, J. T. (2000). Effect of supplementation with organic selenium on mercury status as measured by mercury in pubic hair. Journal of Trace Elements in Medicine and Biology, 14(2), 84–87. https://doi.org/10.1016/S0946-672X(00)80035-8

• Spiller, H. A., Hays, H. L., Burns, G., & Casavant, M. J. (2017). Severe elemental mercury poisoning managed with selenium and N-acetylcysteine administration. Toxicology Communications, 1(1), 24–28. https://doi.org/10.1080/24734306.2017.1392076

• Wang, G., Hong, Q., Mei, J., et al. (2024). Influence of selenium supplementation on mercury levels in hair of metropolitan residents in China: Spatial distribution, impact factors, and antagonism. Expo Health, 16, 1365–1380. https://doi.org/10.1007/s12403-024-00630-y

• World Health Organization. (2024, October 24). Mercury and health [Fact sheet].

  https://www.who.int/news-room/fact-sheets/detail/mercury-and-health

Disclaimer  

This article is for general educational purposes only and does not constitute medical advice. No doctor–patient relationship is created. Always consult a qualified healthcare professional before making any health-related decisions.