Tartare Trouble! What Healthcare Providers Need to Know about Tuna

I don't always cover each of my news segments on MidlevelU as I figure you all as medical providers are aware of the information at hand. But, in reviewing studies, government recommendations, and yes, even a few EPA reports in decoding Consumer Report's most recent recommendations for this Saturday's Fox and Friends appearance, I learned some intriguing information about, well, tuna. I thought you might be interested as well. 

As a sushi lover and woman of childbearing age, any study about fish and pregnancy puts me on high alert. As most of us as nurse practitioners know, fish can contain high levels of mercury so many types are not recommended, or are recommended only in limited amounts, in pregnancy. What I hadn't known is how mercury gets into our food in the first place, and why some fish, including different species of tuna themselves, contain higher levels than others. 

How does mercury get in our food, and why do we care?

Mercury is a neurotoxin and can negatively affect development of the brain and nerves. This is especially true in fetal development where a series of complex steps must occur in a very specific manner to ensure proper brain function in the future. 

Mercury enters our oceans mainly as a result of industrial pollutants. Imagine the stereotypical factory leaking oil next to a river scene and you've pretty much got the picture. The contaminant can also occur naturally, as a result of an erupting volcano, for example. Regardless of the source, mercury seeps into our waters and is absorbed by plants and small ocean critters. Then small fish eat these plants and tiny sea creatures ingesting and absorbing mercury contaminants into their blood and tissues until they are in turn gobbled up by an even larger fish.

The higher you go up the food chain, more mercury has accumulates. This is why sharks, kings of the ocean, contain mercury in notoriously high concentrations. While tuna meat doesn't contain as much mercury as that of sharks, tuna are large fish and therefore contain the toxin in noticeable proportions. 

Why do different types of tuna and different tuna products have varying levels of mercury?

To complicate the tuna safety question even further, different types of tuna, and even individual fish themselves, contain different levels of mercury. Based on the food chain picture I mentioned above, the older and larger a particular fish, the more likely it is to have high mercury content. Restaurants typically serve cuts from very large fish to create a more appealing plate. Large tuna varieties used by your local sushi joint, ahi tuna to name one, contain the most mercury, about 0.5 to 0.75 parts per million (ppm). 

What if the thought of eating raw fish grosses you out and you stick to canned tuna as do many Americans? Unfortunately, the tuna troubles don't get much clearer. Canned albacore tuna, typically labeled as 'chunk white' tuna is universally acknowledged as a relatively high mercury product. A serving of canned albacore contains about 0.5ppm mercury, although you won't see this advertised on the can, of course. Further confusion arises when we look at 'chunk light' tuna. While a serving of this stuff contains just one-third the mercury content of canned albacore tuna, it may not be as innocent as once thought. 

A new Consumer Reports study shows that levels of mercury in so-called 'light' tuna are unpredictable. Like I mentioned earlier, the amount of mercury in seafood depends on the size of the fish and it's age. Since you can't predict if a larger or smaller tunafish made its way into the can of tuna you ate for lunch, you have no idea it there is a chance your 'light' tuna sandwich has high levels of mercury, or not. Consumer Reports says that one in five cans of 'light' tuna have almost twice the amount of mercury as that of others. 

What do different groups say about how much tuna we should eat?

The FDA says consuming 2-3 servings per week of canned 'light' tuna is safe for adults, including pregnant women. When it comes to albacore, or 'chink white' tuna, the organization suggests limiting consumption to one serving per week in adults and none for pregnant women. Consumer Reports takes a more conservative approach recommending that pregnant women consume no tuna whatsoever and that individuals who are not pregnant and not planning to become pregnant consume canned 'light' tuna no more than once per week. 

Mercury consumption carries different levels of risk for us all depending on our size and weight. The larger you are, the more of the toxin your body can tolerate. If you're a canned tuna aficionado and could use some help determining a healthy level of tuna consumption, the Environmental Working Group offers a handy 'Tuna Calculator' on it's website giving both the FDA's and it's own, more conservative, recommendations for your ideal intake of the fish. 

What tuna consumption guidelines will you recommend to your patients?

 

If you missed my Fox and Friends discussion on eating tuna in pregnancy, check it out here!