Why Aren't You Supposed to Eat a Lot of Tuna? Mercury and Moderation

December 12, 2025 •

2 min read

According to Consumer Reports, canned tuna is the second most popular seafood in the U.S., but like many other large fish, it contains varying levels of mercury. So, why aren't you supposed to eat a lot of tuna? The answer lies in managing your intake of this neurotoxin to prevent health risks while still enjoying the fish's nutritional benefits.

Quick Summary

Excessive consumption of tuna, particularly higher-mercury varieties like albacore and bigeye, can lead to the buildup of methylmercury in the body. This can cause neurological problems, especially for vulnerable populations such as pregnant women, young children, and nursing mothers. Health authorities advise limiting intake and choosing lower-mercury options to mitigate risks.

Key Points

Mercury Exposure: The primary reason for limiting tuna intake is its mercury content, particularly methylmercury, a neurotoxin that accumulates in the body over time.
Biomagnification: Larger and older predatory fish, like certain tuna species, have higher mercury levels because they consume smaller, mercury-contaminated fish throughout their lives.
Variety Matters: Canned light (skipjack) tuna contains significantly less mercury than canned white (albacore) or fresh bigeye tuna, making it the safer choice for more frequent consumption.
Vulnerable Groups: Pregnant women, breastfeeding mothers, and young children are most susceptible to mercury's harmful effects on neurological development and should limit or avoid tuna entirely.
Moderation is Key: For healthy adults, consuming tuna in moderation is safe and provides nutritional benefits like protein and omega-3s, but excessive intake risks mercury poisoning.
Health Risks: High mercury exposure can lead to neurological symptoms like memory loss, tremors, and impaired coordination, and can cause developmental issues in children.
Look for Alternatives: To reduce mercury exposure, consider other nutritious, low-mercury seafood like salmon, shrimp, and sardines, which offer similar health benefits.

The Mercury Concern: Why Tuna Consumption Needs Limits

The primary reason for limiting tuna consumption is the risk of mercury exposure, specifically methylmercury. Methylmercury is a neurotoxin that can have harmful effects on the brain and nervous system if it accumulates in the body. Tuna, being predatory fish high on the food chain, accumulate mercury from the smaller fish they eat through a process called biomagnification. The mercury content is generally higher in older and larger tuna species. This necessitates varying dietary recommendations based on the type of tuna consumed. While moderate amounts of lower-mercury tuna are typically safe, regular, high intake can lead to mercury poisoning, with symptoms ranging from mild tingling to severe neurological issues.

Mercury Levels in Different Tuna Types

Mercury levels vary significantly between different tuna types. Skipjack, used in most canned light tuna, has lower levels than albacore and bigeye. The FDA categorizes fish based on mercury content, with canned light tuna often in the 'Best Choices' category and canned albacore in the 'Good Choices' category. Fresh tuna, particularly bigeye, can have the highest mercury levels.

At-Risk Populations and Recommendations

Groups like children, infants, pregnant individuals, and breastfeeding mothers are more susceptible to mercury's harmful effects and should be cautious about their fish intake. Mercury can impact fetal brain development. Some sources, like Consumer Reports, even suggest pregnant people avoid all tuna. For the general adult population, moderate consumption of lower-mercury tuna is typically safe and provides nutritional benefits.

Health Implications of Mercury Exposure

High mercury levels from excessive consumption are linked to impaired brain and nervous system function.

Potential Effects Include:

Impaired fine motor skills and coordination
Memory loss and speech difficulties
Tingling sensations
Developmental delays and learning disabilities in children
Links to fertility issues and blood pressure regulation in adults

Making Smarter Seafood Choices

Varying seafood choices helps balance the benefits of fish with mercury risks. The FDA and EPA offer guidelines for making informed decisions. Low-mercury options like salmon, sardines, and shrimp are good alternatives.

Tuna Variety vs. Mercury Level


Tuna Type	Mercury Level (Approx.)	Serving Suggestion (Adults)	Notes
Canned Light (Skipjack)	Lowest	2-3 servings per week (approx. 8–12 oz)	'Best Choice' category.
Canned White (Albacore)	Higher	1 serving per week (approx. 4 oz)	'Good Choice' category.
Fresh/Frozen (Yellowfin)	Higher	Limit to one serving per week	Be mindful of portion size.
Fresh/Frozen (Bigeye)	Highest	Limit greatly or avoid	Highest mercury concentration.

Conclusion

While tuna is nutritious, its mercury content necessitates limits on consumption. Moderation and choosing lower-mercury species are key to safely including tuna in your diet. Canned light tuna is generally a safer option than higher-mercury varieties. Vulnerable populations may need to avoid tuna entirely. Understanding these risks and recommendations from health authorities enables balanced dietary choices.

Visit the FDA's Fish Consumption Guidelines for more information

Frequently Asked Questions

Early symptoms of mercury poisoning can include tingling sensations in the extremities (fingers, toes, lips), irritability, memory loss, and difficulty with fine motor coordination.

Health authorities generally recommend that adults consume 2 to 3 servings (8 to 12 ounces) of canned light tuna per week, assuming no other high-mercury fish are consumed.

Yes, on average. Canned light tuna typically uses smaller skipjack tuna, which have lower mercury levels. Fresh or frozen tuna, especially varieties like bigeye, often come from larger, older fish with higher mercury concentrations.

Mercury can negatively impact the developing brain and nervous system of a fetus or young child. A child's faster growth rate and higher ratio of food intake to body weight make them more susceptible to mercury's effects.

Excellent low-mercury alternatives include salmon, shrimp, sardines, cod, and catfish. These can provide similar nutritional benefits, like omega-3 fatty acids, with less risk of mercury exposure.

No, cooking does not reduce or eliminate the mercury in tuna. The methylmercury is bound to the fish's tissue and is not destroyed by heat.

While mercury is the main concern, some canned tuna can also contain high levels of sodium. Additionally, over-relying on any single food, including tuna, can lead to a diet lacking in a variety of other essential nutrients.