Mercury (Hg)
Mercury is a toxic heavy metal with no useful role in the body.
Also known as: Hg, blood mercury, methylmercury
In blood, it mainly comes from methylmercury in fish and seafood, especially large predatory fish such as tuna, swordfish, shark and pike. Over time, too much mercury can affect the nervous system and the kidneys, and the developing brain of an unborn child is the most sensitive. Your blood level reflects your intake over the past weeks to months. Mercury from dental amalgam fillings or from some jobs shows up mainly in urine rather than blood, so this test is best at showing exposure through your diet.
Why this matters
Since mercury serves no purpose in the body, lower is always better. It can quietly accumulate and affect your nervous system and kidneys long before you notice anything. Early signs include slight hand tremor, trouble concentrating, mood changes, and tingling in fingers or toes.
Pregnant women should pay special attention, as mercury levels considered harmless for adults can affect fetal brain development.
The most common sources are predatory fish (swordfish, tuna, shark, pike), amalgam fillings, and certain workplaces.
How this connects to other biomarkers
- Mercury blocks Selenium from doing its job as an antioxidant, so high mercury can cause a functional Selenium shortage even if your Selenium level looks normal. It can also increase inflammation (reflected in CRP) and strain the kidneys, which may show up as rising Creatinine or declining GFR before you feel any symptoms.
How often should I test Mercury (Hg)?
There is no routine schedule for testing mercury. A single test is useful if you eat large predatory fish such as tuna or swordfish several times a week, or may be exposed through your job or a hobby. If your value is raised, retest about 3 months after cutting back, since blood mercury takes a few months to fall.
At baseline / for screening: Once, if you eat large predatory fish several times a week or may be exposed through your job or a hobby.
When monitoring an intervention or change: About 3 months after cutting back on high-mercury fish, to confirm the level is falling.
Note: Avoid fish, seafood and seaweed for 48 hours before your blood draw, as they can temporarily raise your mercury value.
Sources
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