🧪 Hidden Exposure: How Mercury Builds Up in Your Thyroid—and Your Brain

July 2025

Most people know mercury as a toxic metal—something to avoid in fish or old thermometers. But new science suggests mercury may be silently building up in two critical parts of our bodies: the thyroid gland and the brain.

A fascinating study published in PLOS ONE by Pamphlett and colleagues in 2021 examined 115 human thyroid glands across a wide age range. Using advanced imaging techniques, the researchers found that mercury accumulates in thyroid follicular cells as people age. While only 4% of young people (ages 1–29) showed mercury in their thyroids, that number jumped to 38% in people over age 60.

Even more concerning?

Mercury was often found alongside other toxic metals like cadmium, lead, and nickel—all of which may work together to damage cells.

🧠 Why Mercury Sticks Around: A Cellular Perspective

So, why does mercury build up in the thyroid—and the brain—in the first place? The answer lies in chemistry, transport mechanisms, and cellular detox limits.

1. Thiol Attraction: Mercury’s Chemical Magnet

Mercury, particularly in its inorganic form, has a high affinity for sulfhydryl groups (–SH)—the same sulfur-based molecular structures found in proteins and antioxidants like glutathione. These –SH groups are abundant in both thyroid follicular cells and neurons, making these tissues natural “magnets” for mercury.

In healthy cells, glutathione binds mercury and helps eliminate it. But with age, oxidative stress, or nutritional deficiencies (like low selenium), this system can be overwhelmed. Mercury then latches onto structural proteins and enzymes, disrupting cellular functions and promoting long-term toxicity.

2. Molecular Mimicry: Mercury’s Sneaky Passport

Methylmercury—the organic form found in seafood—can mimic amino acids like methionine. This allows it to piggyback into cells via amino acid transporters:

• In the brain, it crosses the blood–brain barrier by disguising itself as methionine–cysteine, entering neurons through LAT1 transporters.

• In the thyroid, it likely uses similar pathways, though the exact transporters are still being identified.

Once inside the cell, methylmercury is slowly converted into inorganic mercury, which becomes trapped and difficult to excrete.

3. Limited Exit Strategies

Neurons and thyroid cells have limited detoxification capacity. Unlike liver or kidney cells that are loaded with export pumps and regenerative ability, these tissues lack robust efflux systems, allowing mercury to accumulate slowly over decades.

In both tissues, mercury interferes with:

• Energy production (by damaging mitochondria),

• Hormone production (in the thyroid),

• Cognitive function and emotional regulation (in the brain).

⚠️ Health Implications: More Than a Trace Concern

The study raises the possibility that mercury could contribute to common thyroid diseases, including:

• Autoimmune thyroiditis (e.g., Hashimoto’s),

• Hypothyroidism, and

• Thyroid cancer.

In the brain, chronic mercury exposure is already linked to neurodevelopmental delays, neurodegeneration, and psychiatric conditions. The fact that both the thyroid and brain are targets for mercury suggests a shared vulnerability—one rooted in molecular biology and exacerbated by modern environmental exposures.

🐟 What Can You Do?

Mercury exposure today largely comes from:

• Seafood (especially large predatory fish like tuna and swordfish),

• Dental amalgams (older fillings), and

• Air pollution (coal combustion remains a major global source).

To reduce your risk:

• Limit exposure frequency or choose low-mercury fish like salmon, sardines, or trout.

• If you have many amalgam fillings, talk to your dentist about your options.

• Support detoxification with selenium-rich foods (like Brazil nuts), glutathione precursors (like N-acetylcysteine), and a healthy antioxidant-rich diet.

🔍 The Takeaway

Mercury doesn’t just disappear. It bioaccumulates—quietly embedding itself in our most sensitive tissues over time. Thanks to advanced research like this PLOS ONE study, we’re beginning to understand how that happens and what it might mean for our health.

As science advances, it’s becoming clear: what we’re exposed to today could affect the hormones we produce, the mood we feel, and the clarity with which we think tomorrow.

References:

Pamphlett R, Doble PA, Bishop DP. Mercury in the human thyroid gland: Potential implications for thyroid cancer, autoimmune thyroiditis, and hypothyroidism. PLOS ONE. 2021;16(2):e0246748.https://doi.org/10.1371/journal.pone.0246748

#Mercury bioaccumulation, #Thyroid toxicity, #Neurotoxicity, #Heavy metals, #Environmental exposure