In Reply
The letter from Grandjean et al agrees with our Viewpoint1 that fish eaten during pregnancy benefits the developing brain but disagrees that consumption beyond what most people eat is necessary to cause harm from mercury. Consumption advice from the US Food and Drug Administration and Environmental Protection Agency in 2017 omitted any mention of this important benefit. It only advised that fish consumption benefits growth and development generally, as with other high-protein foods. The takeaway was that benefits from fish are obtainable from other foods without mercury-based consumption limitations that the 2017 advice recommends for fish. We question whether this advice can motivate fish consumption during pregnancy. Most pregnant women under-consume fish. It was hoped that new advice would help correct that shortfall.
We also argued that the mercury-based limitations add to the problem by being excessive and potentially scaring pregnant women away from fish consumption. The advice was designed to keep exposures less than Environmental Protection Agency’s reference dose for mercury. The process used to develop the reference dose was not designed to account for benefits. In that respect, the reference dose is essentially a level for mercury but not for fish. There can be a difference between risk of harm from mercury alone and risk of harm from mercury in the presence of countervailing benefits. For example, children in the United Kingdom whose mothers ate no fish but were exposed to mercury during pregnancy experienced deficits in IQ while children whose mothers ate fish and were exposed to the same levels of mercury experienced gains.2
We are not suggesting that mercury in fish is irrelevant. In a US study,3 more than 2 servings per week of fish coupled with lower mercury exposure was associated with greater neurocognitive benefits than more than 2 servings per week coupled with greater mercury exposure. Mercury appears to have affected the size of the benefits but did not eliminate them. Consumption of more than 2 servings was still associated with greater benefits than consumption of two or less servings. Fish consumption advice should reflect this kind of net benefit.
Fish consumption advice can also reflect the circumstances under which mercury exposure can overtake benefits and cause adverse neurocognitive effects. In the Seychelles Islands, beneficial effects on psychomotor outcomes decreased as methylmercury increased, and the benefits went away at 11 ppm in hair.4 This level of mercury is nearly twice as high as the 99.9th percentile of all exposure in the United States.5 We estimate that it would take 175 oz per week of commercial fish in the United States containing an average level of mercury to reach that exposure.
In summary, we agree with Grandjean et al that neurocognition is an important benefit from fish consumption. We also agree that excessive mercury can be harmful. However, the net benefit from fish consumption is great enough that the precautionary consumption limitations in the 2017 advice risk scaring women away from fully benefiting or potentially from eating fish at all.
Footnotes
Conflict of Interest Disclosures: Mr Spiller discloses being the former director of the Office of Seafood in the US Food and Drug Administration. Mr Landa discloses being the former director of the US Food and Drug Administration’s Center for Food Safety and Applied Nutrition. No other disclosures were reported.
Contributor Information
Philip Spiller, Retired former Director, Office of Seafood in the US Food and Drug Administration’s Center for Food Safety and Applied Nutrition.
Carolyn T. Bramante, Division of General Internal Medicine, Department of Medicine, University of Minnesota, Minneapolis; Division of General Pediatrics and Adolescent Medicine, Department of Pediatrics, University of Minnesota, Minneapolis.
Michael Landa, Retired former Director, US Food and Drug Administration’s Center for Food Safety and Applied Nutrition.
References
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