Nutrition Myths
How much canned tuna is safe to eat?

SUMMARY

  • There are two main types of canned tuna: “white/albacore” or “light”.
  • “White/albacore” tuna contains about three times more mercury than “light” tuna.
  • Most of the mercury in fish is in the form of a highly toxic methylmercury compound.
  • To avoid mercury toxicity, restrict the weekly intake depending on your body weight.
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How much canned tuna is safe to eat?

In the U.S. population, somewhere between 39% and 43% of the total mercury intake from fish and seafood comes from tuna consumption. The reason for such a high percentage is because it is the most consumed fish.

Major tuna sources of mercury are: canned tuna (28%) of which light tuna contributes 18% and albacore/white tuna which contributes 10%.

Fresh or frozen tuna accounts for 11%. (1)

Three types of tuna are used for canning: albacore, skipjack and yellow-fin tuna.

Studies have found that some of these species contain a higher amount of mercury than others.

The amount of mercury accumulated in fish depends on a number of factors such as the size and age of the fish. (2)

Here is a description of the various types of tuna we consume (3):

Albacore tuna is primarily sold as canned tuna and labelled as “white” tuna meat. It grows up to 80 pounds and lives up to 12 years.

Skipjack Tuna is primarily sold as canned tuna and labelled “light” tuna. It grows up to about 8 pounds.

Yellow-fin Tuna: only a small amount is canned and labelled as “light” tuna. It is primarily served as steaks and loins. It is usually mixed with Skipjack tuna. It grows up to 400 pounds and lives up to 7 years.

Bigeye Tuna is not used for canning. It is used for sashimi, sushi and served as steaks or loins. It grows up to 6.5 feet long and lives up to 10 years.

Bluefin Tuna is used mostly for sashimi or sushi. It grows up to 1200 pounds and lives up to 30 years.

The following data have been extracted from the report published by FDA from the studies done between 1990 and 2010.

Please note that other studies not included in this report may show slightly different concentrations of mercury in particular species, but the differences are not significant.

Usually there is a consistency in levels between the specific species.

The results of the study show an average concentration of mercury (middle column) and highest recorded (right column).

The term “ppm” means parts per million. For example, 1ppm means 1 milligram of mercury per kg of fish flesh.

In addition to canned tuna, I also included other types of tuna available from the report for comparison.

This additional information will be useful as a warning for those who frequent sashimi bars.

Note: Bluefin tuna was not included in the report but being a large predatory fish that lives for 30 years, mercury levels are in the high range.

Mercury Levels in Tuna (1990-2010) (4)

Tuna typeAverage (ppm)Highest (ppm)mcg/oz
Tuna (canned, light)0.1280.8893.6
Tuna (fresh/frozen, Skipjack)0.1440.264
Tuna (canned, albacore)0.350.8539.8
Tuna (fresh/frozen, Yellowfin)0.3541.4789.9
Tuna (fresh/frozen, Albacore)0.3580.8210
Tuna (fresh/frozen, Bigeye)0.6891.81619.3

As can be seen from the table, the types of tuna which are usually served as sashimi or as a steak contain much higher amounts of mercury.

The following table shows the calculation of the maximum weekly amount of tuna you can eat depending on your body weight. An example of the calculations is shown at the bottom of this article.

Weekly safe limits of tuna

Body
Weight (kg)
Limit of mercury
(mcg/week)
Weekly Limit (oz)
Light Canned
Weekly Limit (oz)
White Canned
Weekly Limit (oz)
Skipjack
Weekly Limit (oz)
Yellowfin (oz)
Bigeye (oz)
50359.73.68.83.51.8
604211.74.310.54.22.2
704913.6512.34.92.5
805615.65.7145.72.9
906317.56.415.86.43.3
1007019.47.117.57.13.6

How to read the table above:

If your weight is 80kg, your weekly safe limit is 56 mcg of mercury. This means that you will reach your safe weekly limit of mercury by eating either:

  • 15.6 ounces of canned “light” tuna, or
  • 5.7 ounces of canned “white albacore” tuna, or
  • 14 ounces of Skipjack tuna, or
  • 5.7 ounces of Yellow tuna, or
  • 2.9 ounces of Bigeye tuna.

Any extra fish that week may exceed the safe level of mercury recommended since almost all fish contain some traces of mercury. (2)

Calculation example:

If you weigh 50kg how much of white/albacore tuna you can eat per week?

  • White/albacore canned tuna contains on average 0.35 ppm of mercury.
  • 0.35 ppm (parts per million) means that there is 0.35 micrograms (mcg) of mercury in one gram of tuna flesh.
  • 50 kg person’s safe weekly limit for mercury is 35 mcg.
  • 1 ounce = 28 g
  • 0.35 x 10-6 of mercury per gram of tuna times 28g of tuna =0.0000098
  • This means that there is 9.8*10-6 or 9.8 mcg of mercury in 1 oz. (28g of tuna)
  • 35 mcg weekly mercury limit divided by 9.8 micrograms (in 1 oz.) = 3.6 ounces
  • Answer: 35 mcg of weekly safe limit for a 50kg person is reached by consuming 3.6 ounces of canned white/albacore Tuna.

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