Fishy Mercury Warning

The Food and Drug Administration just issued a new warning to pregnant women about mercury in seafood (search). You can “protect your baby” from developmental harm by following three rules, claims the FDA.

But there’s no evidence that the rules will protect anyone and they’re only likely to foster undue concern about an important part of our food supply.

“Do no eat shark, swordfish, king mackerel or tilefish because they contain high levels of mercury,” is the FDA’s first rule.

It’s certainly true that such larger fish tend to have higher levels of mercury in their tissue since mercury levels tend to accumulate up the food chain. But unless women are consuming fish that have been exposed to industrial-level concentrations of mercury for extended periods of time — as Japanese women in the vicinity of Minamata Bay did during the 1950s — it’s not at all clear that consuming large fish is any sort of health risk.

Researchers from the Harvard School of Public Health (search) recently reported in the Journal of Occupational and Environmental Medicine (Feb. 2002) that they could not find mercury-related health effects among a group of regular swordfish consumers.

Although a “significant relationship between fish consumption and blood mercury concentrations” was identified by the researchers, “higher blood mercury concentrations were, however, not associated with specific patterns of health complaints.”

There is also no evidence of a general threat to infants and children from typical maternal consumption of fish with typical mercury concentrations.

“No evidence of adverse effect from either pre- or post-natal exposure to methyl mercury,” is how Thomas W. Carson of the University of Rochester School of Medicine characterizes the results of an ongoing study of children in the Seychelles Islands.

In fact, “a surprising finding in the results of the examination of children at 66 months of age was that several [intelligence] tests scores improved as either pre- or post-natal mercury levels increased… linear regression analysis reveals statistically significant beneficial correlations,” noted Dr. Carson.

That’s exactly the opposite situation of what the FDA claims as the basis of its warning!

Aside from Minamata Bay, not a single clinical case of mercury poisoning associated with fish consumption is to be found in the scientific literature, according to Dr. Carson.

It seems the FDA is warning (scaring?) us about a scenario that has, essentially, never occurred.

The FDA’s other two rules are similarly not grounded in science.

“Levels of mercury in other fish can vary. You can safely eat up to 12 ounces (two to three meals) of other purchased fish and shellfish per week. Mix up the types of fish and shell fish you eat and do not eat the same type of fish and shellfish more than once a week,” warns the FDA’s second rule.

Now where did the 12 ounces-per-week figure come from? Is there evidence that consuming 13 ounces per week — or for that matter, 130 ounces per week — is dangerous? Is there evidence that eating the same type of fish and shellfish more than once a week is harmful?

The FDA’s 12 ounces-per-week rule is simply arbitrary.

The third FDA rule reads, “Check local advisories about the safety of fish caught by family and friends in your local rivers and streams. If no advice is available, you can safely eat up to 6 ounces (one meal) per week of fish you catch from local waters, but don’t consume any other fish during that week.”

The FDA apparently wants us to think that any given local body of water is potentially a Minamata Bay (search) situation, where tons of mercury were dumped into the water over the course of two decades. But even if such situations existed in the U.S. — and they never have — the Minamata Bay mercury poisoning victims no doubt consumed much more fish than one six-ounce meal per week.

Seafood is most definitely part of a healthy diet. Further, the seafood industry is a large part of our economy. Unless the FDA has a science-based health warning to issue, it ought to clam up.

Steven Milloy is the publisher of, an adjunct scholar at the Cato Institute and the author of Junk Science Judo: Self-Defense Against Health Scares and Scams (Cato Institute, 2001).

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