Understanding Mercury in Tuna
Mercury is a naturally occurring element, and its most concerning form, methylmercury, accumulates in marine food chains. Tuna, being a predatory fish, absorbs mercury from smaller fish it consumes throughout its life, leading to higher concentrations in larger and older specimens. Factors influencing mercury levels in tuna include the species, age, size, and even the geographic location where it was caught.
The Mercury Food Chain Explained
The biomagnification process is why a bigeye tuna has significantly more mercury than a small skipjack tuna. Smaller marine organisms absorb small amounts of methylmercury from the water. Smaller fish then eat these organisms, and larger predatory fish, like tuna, consume the smaller fish. With each step up the food chain, the concentration of mercury increases, meaning larger, longer-living predators carry the highest levels.
Canned Tuna vs. Fresh Tuna
The preparation of tuna—canned or fresh—doesn't inherently change mercury levels, but the type of fish used does. Canned light tuna, which is typically made from smaller, younger skipjack tuna, contains much lower mercury levels than fresh or canned albacore. The larger, older tuna species like bigeye are generally sold as fresh or frozen steaks, which is why fresh tuna can often have higher mercury concentrations.
Which Tuna is Lowest in Mercury?
Based on data from the U.S. Food and Drug Administration (FDA) and other research, some tuna varieties stand out as having consistently lower mercury levels. Your best options are canned light tuna and skipjack, while albacore, yellowfin, and especially bigeye tuna should be consumed more sparingly.
- Canned Light Tuna (Skipjack): This is the top choice for minimal mercury exposure. Canned light tuna often contains skipjack, a smaller, faster-growing species with a shorter lifespan. This means less time to accumulate mercury.
- Wild Planet Tuna: Some brands, like Wild Planet, specifically source smaller, younger migratory tuna caught using pole-and-line or troll-caught methods. This fishing practice targets fish with naturally lower mercury content.
- Yellowfin Tuna: While higher in mercury than skipjack, fresh or frozen yellowfin is considered a "Good Choice" by the FDA and can be enjoyed in moderation.
- Albacore Tuna (White Tuna): Often used for canned white tuna, albacore has approximately three times the mercury of canned light tuna. Health authorities recommend limiting intake to about one 4-ounce serving per week.
- Bigeye Tuna: This large, long-lived species has the highest mercury concentration of the common tuna varieties and should be avoided, especially by pregnant women and children.
Tuna Mercury Levels Comparison
The following table summarizes the typical mercury levels for various tuna products, based on FDA data, and provides corresponding consumption recommendations.
| Tuna Type | Average Mercury (ppm) | Consumption Category | Recommended Weekly Servings (Adult) |
|---|---|---|---|
| Canned Light (Skipjack) | ~0.126 | Best Choice | 2–3 (up to 12 oz) |
| Fresh/Frozen Skipjack | ~0.144 | Best Choice | 2–3 (up to 12 oz) |
| Canned Albacore | ~0.350 | Good Choice | 1 (up to 6 oz) |
| Fresh/Frozen Yellowfin | ~0.354 | Good Choice | 1 (up to 6 oz) |
| Fresh/Frozen Bigeye | ~0.689 | Choice to Avoid | 0 |
Making Healthier Tuna Choices
To minimize your mercury intake, focus on selecting the right type of tuna and paying attention to portion sizes. Opt for canned light tuna (which is usually skipjack) over canned albacore for your weekly meals. For fresh tuna, choose smaller yellowfin over bigeye. When shopping, you can also look for certifications like those from the Marine Stewardship Council (MSC), which can sometimes provide more detail about the species and fishing method used.
Conclusion: Safe and Nutritious Tuna Consumption
Enjoying tuna as part of a healthy diet is possible by making smart choices. For the lowest mercury content, choose canned light tuna (skipjack) and limit consumption of larger, higher-mercury species like albacore and bigeye. This strategy allows you to benefit from the omega-3 fatty acids and protein tuna provides while minimizing exposure to methylmercury. Pregnant and breastfeeding individuals should be particularly vigilant and may choose to avoid tuna entirely in favor of other low-mercury fish. A balanced approach to seafood consumption is the key to both health and peace of mind.
How to Choose the Safest Tuna
- Prioritize Skipjack: For the lowest mercury, consistently choose canned light tuna, which is typically skipjack.
- Limit Albacore: Restrict canned albacore (white) tuna to no more than one 6-ounce serving per week for adults due to its higher mercury level.
- Avoid Bigeye: Steer clear of bigeye tuna, often used in sushi, as it contains the highest mercury levels.
- Monitor Brands: Some brands, like Wild Planet, use specific fishing methods targeting smaller, lower-mercury fish.
- Vary Your Fish: Alternate tuna with other low-mercury fish like salmon, sardines, and tilapia to diversify your nutrient intake.
- Check Labels: Some labels might indicate “pole-and-line caught” or list the species, giving you more information about what’s inside.
- Consider Alternatives: For high omega-3s, consider low-mercury fish such as wild-caught salmon and sardines.
Mercury in Tuna FAQs
Which type of canned tuna has the lowest mercury?
Canned light tuna, which typically contains skipjack, has the lowest mercury content of all canned tuna options.
Why does albacore tuna have more mercury than light tuna?
Albacore are larger and live longer than skipjack tuna (used for light tuna), allowing more time for mercury to accumulate in their tissues.
How much canned tuna is safe to eat in a week?
For most adults, the FDA recommends 2–3 servings (up to 12 ounces) of canned light tuna per week, or just 1 serving (up to 6 ounces) of albacore.
Is it safe for pregnant women to eat tuna?
While some authorities recommend a limited amount of canned light tuna, some food safety experts advise pregnant women to avoid tuna entirely due to unpredictable mercury spikes in individual cans. Low-mercury alternatives like salmon are generally safer.
Does mercury levels vary between brands?
Yes, mercury levels can vary significantly between brands, even within the same type of tuna. Testing by groups like Consumer Reports has shown unpredictable spikes in some individual cans.
What happens if you eat too much tuna with high mercury?
High exposure to mercury can lead to chronic mercury poisoning, with symptoms including neurological issues, muscle weakness, and impaired vision or hearing.
Can you reduce the mercury in tuna?
There is no effective method for reducing the methylmercury content in tuna once it has been absorbed by the fish. The best approach is to choose lower-mercury species and control portion sizes.
