Eating tuna and other large fish is the most common way people are exposed to methylmercury. Methylmercury is a neurotoxin that can accumulate in the body over time and cause adverse health effects. Understanding how long tuna mercury stays in your system can help guide safe consumption.
How does mercury get into tuna?
Mercury occurs naturally in the environment from volcanic activity, forest fires and breakdown of minerals. It makes its way into the ocean and accumulates in the tissues of fish as methylmercury. Large, predatory fish like tuna bioaccumulate high levels of mercury by eating many smaller fish over their long lifespans.
The older and larger the tuna, the higher the levels of mercury. Mercury builds up in muscle tissue, so tuna steaks have more mercury than canned tuna made from smaller, younger fish. Albacore (white) tuna generally contains more mercury than light tuna.
How is methylmercury absorbed and excreted?
When you eat tuna, the methylmercury is almost completely absorbed into your bloodstream through your digestive tract. From there, it’s distributed to all tissues in the body, including the brain. Methylmercury crosses the blood-brain barrier and bioaccumulates in the brain over time.
Methylmercury is primarily excreted through bile and feces. A small amount is also excreted in urine, hair, nails and breast milk. Excretion rates vary between individuals based on metabolism and overall health.
How long does tuna mercury stay in the body?
On average, it takes about 2 months for half of the methylmercury to be eliminated from the body. This is called the biological half-life. However, the full elimination of methylmercury takes much longer due to ongoing accumulation in body tissues.
Studies have found it can take up to 70-80 days for blood methylmercury levels to decrease by 50% after exposure stops. For total body burden, the biological half-life is typically 1-3 months in adults and can be twice as long in young children.
To consider total body elimination, it’s estimated that methylmercury has a half-life of 50-70 days in adults. This means full excretion takes 4-5 half-lives, or about 7-11 months for adults. For infants and children, their lower body weight and still-developing brain and metabolism means it likely takes over a year to eliminate tuna mercury.
Factors that affect elimination time
Several factors can influence the excretion rate and total time methylmercury stays in the body:
- Age – Children, babies and fetuses eliminate mercury slower
- Sex – Females clear mercury slower than males
- Genetics – Gene variation impacts mercury metabolism
- Overall health – Diseases and conditions can impair excretion
- Frequency of exposure – Frequent tuna meals increase bodily accumulation
Can tuna mercury accumulation cause symptoms?
As methylmercury accumulates, it can begin causing symptoms depending on the level of exposure. Mild symptoms may include:
- Numbness and tingling in hands and feet
- Impaired cognitive function and memory
- Difficulty articulating thoughts and speech
- Blurred vision or decreased hearing
- Lack of coordination and poor motor skills
Higher mercury levels can lead to more severe effects like:
- Irreversible brain and nervous system damage
- Kidney toxicity
- Cardiovascular problems
- Respiratory failure
- Birth defects (if exposed during fetal development)
Symptoms depend on how much mercury builds up over time and how long exposure occurs. The population most vulnerable to mercury’s toxic effects are children and pregnant/nursing women.
How much tuna can you safely eat?
To avoid mercury build-up while still enjoying the health benefits of seafood, follow these FDA/EPA guidelines for safe tuna consumption:
| Group | Recommended Limit |
|---|---|
| Children under 6 | 1-2 servings light tuna per week |
| Children 6-12 | 2-3 servings albacore tuna per month |
| Women who are or may become pregnant | 2-3 servings light tuna per week |
| Women who are nursing | 2-3 servings light tuna per week |
| Men and women over 12 | 5 servings albacore tuna per week |
A serving is about 3-4 ounces of tuna. Follow these tips for choosing lower-mercury tuna for maximum safety:
- Choose light tuna over albacore/white tuna
- Avoid large, mature tuna like bluefin
- Check tuna guides to pick sustainable, low-mercury species
- Limit consumption of other high-mercury fish like swordfish and marlin
- Vary seafood choices to minimize exposure to any one toxin
How to reduce tuna mercury levels
If you’ve consumed high amounts of tuna and are concerned about potential mercury exposure, here are some steps to help eliminate it from your body faster:
- Stop eating tuna and other high-mercury fish – Prevent further accumulation and allow existing mercury to clear.
- Eat more fiber – Aids elimination through stool. Focus on fruits, vegetables, whole grains.
- Take probiotics – Healthy gut flora binds with mercury to reduce absorption and facilitate detoxification.
- Eat sulfur-rich foods – Sulfur helps metabolize and excrete heavy metals. Good sources include garlic, onions, eggs, legumes.
- Stay hydrated – Water supports detoxification and prevents mercury reabsorption during excretion.
- Sweat – Activities like sauna use and exercise help eliminate toxins through perspiration.
- Consider chelation therapy – IV chelation under medical supervision may be an option for severe mercury toxicity.
Should you get tested for mercury?
Testing can measure current blood or urine mercury levels, but does not assess total body burden. Hair analysis provides a rough estimate of long-term exposure over months. Testing may be advisable if you:
- Frequently eat seafood high in mercury
- Show possible symptoms of mercury toxicity
- Have certain medical conditions that increase mercury absorption and retention
- Are pregnant or planning to become pregnant
- Want to establish a baseline level of exposure
Discuss any concerns about mercury exposure and testing options with your healthcare provider.
Conclusion
Methylmercury from tuna can accumulate in the body over months to years before it is fully excreted. To reduce mercury levels, limit tuna intake based on guidelines for your age and sex. Pregnant women, nursing mothers and young children need to be especially cautious with tuna consumption due to increased risks. A well-balanced diet with a variety of low-mercury seafood remains an important part of a healthy lifestyle.
