Revisiting the issue of mercury in fish (can I eat a tuna sandwich yet?)

Tuna sandwich on a plate

Like many people, I’ve been concerned about consuming mercury in fish.

So I was fascinated to run across this report from Vital Choice providing some interesting clarification on the issue (it was originally posted a little over a year ago). As a born-again media skeptic, I’ve noted all too often that when the simplest (and usually most alarming) part of a health issue is presented, a new “common sense guideline” is born. Mercury in fish would seem to be a case in point. Pregnant women are encouraged to limit their consumption of many kinds of fish; and, in particular, tuna.

Here’s the overview:

Selenium, an essential mineral, binds tightly to any methyl mercury present, preventing mercury uptake. But if selenium levels are low, the body will try to use the mercury molecules in its place – and someone can end up with a nasty wallop of the stuff, with negative consequences. The protection of selenium occurs even when it’s present in the same food as the methyl mercury…like, um, fish.

And here comes the beauty part: Fish are, overall, one of the richest sources of selenium out there. (Brazil nuts are higher, but you can actually get too much selenium from them because of this, which has its own downside. And personally, I don’t much like them, anyway.) Shrimp, halibut, tuna, cod, salmon, all great sources of this important nutrient, which is an antioxidant, a thyroid support, and a joint protector – and which has the nice habit of binding to methyl mercury.

The online bastion of medical references, PubMed, has a report posted showing that essentially all fish have enough selenium present to bind to any methyl mercury present. In the words of the researchers, “The results show that MeHg [methyl mercury] in all fishes is very low bioaccessible in both gastric and intestinal digestion.”

Selenium deficiency can happen when we live in an area where the soil levels are low (parts of the Pacific Northwest, parts of the Great Lakes region moving eastward toward the New England states, and parts of the Atlantic Coast). It can also happen when we take anti-inflammatory corticosteroid drugs, which deplete selenium supplies. (Ironic given the fact that joint pain is one of the indications of a potential selenium deficiency.)

Mercury can get into our body in other ways, too: some face creams from third-world countries, as well as some Chinese herbs and the like, can be contaminated with mercury and other toxins. And let’s not forget “silver” amalgams, which are mostly mercury.

Does it mean that methyl mercury is not a problem? No. But it means that our choices need to be much more intelligently made, more nuanced. Sure, go ahead and have your fill of naturally low-mercury fish and shellfish (wild-caught salmon and shrimp, for instance.) But also don’t hesitate to eat fish which have a high ratio of selenium to mercury. That would include tuna (especially albacore), one of the fish we’re told is a problem.

As always, the full story is not quite as neat and tidy as the quick, headline-grabbing report might lead us to believe.

One thought on “Revisiting the issue of mercury in fish (can I eat a tuna sandwich yet?)

  1. Pingback: Clarence Darrow and food safety | For Love of Food

Leave a Reply

Your email address will not be published. Required fields are marked *