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Is it true that pregnant women should not eat tuna or salmon due to the high mercury content of these foods?

Introduction

On July 25, 2002, the U.S. Food and Drug Administration (FDA) did indeed issue a caution for pregnant women and nursing mothers related to the consumption of canned tuna. The FDA stopped short, however, of telling pregnant women not to eat any tuna at all. "Nobody wants to tell people to stop eating tuna fish," said the panel chairman, Sanford Miller of Virginia Tech University. "We're trying to balance the very positive virtues of fish, including tuna fish, with the harms. It's a very hard balance to make."

The tuna controversy

Consumption of tuna has been a controversy long before this statement issued by the FDA, however. In several states, including Vermont, Minnesota, Michigan and New Jersey, state governments have already put a 7-ounce per week limit on consumption of tuna by pregnant women or nursing mothers, and even this 7 ounces is considered too high if other mercury-containing fish are eaten during the week. (In that case, 7 ounces total mercury-containing fish would be the total.)

Interestingly, in its statement of July 25, 2002, the FDA chose not to add canned tuna to its already-existing list of fish that it has said pregnant women should not eat at all. This list of fish includes swordfish, king mackerel, shark and tilefish. Several not-for-profit, environmental and health organizations, including the Environmental Working Group and Mercury Policy Project, criticized the FDA for issuing a caution against tuna consumption, but not adding tuna to the list of fish that should absolutely not be eaten by pregnant women and nursing mothers. In response to this criticism, at the exact same time when we are writing this response to your question, the FDA is convening a panel to decide if tuna should be added to its list of fish that should not be eaten by pregnant women or nursing mothers.

Fish in the diet - an individual perspective

But we believe it's important for all individuals, including all pregnant women and nursing mothers, to look more closely at their health status and their food intake, and decide about fish consumption based on these individualized factors. Some pregnant women and nursing mothers may be able to consume limited amounts of canned tuna and not put their babies at risk, because their overall diet has very low levels of other contaminants, and they have good nutrient supplies and great detoxifying ability. Other pregnant women and nursing mothers may be putting their babies at risk due to higher levels of contaminants in their diet, depleted nutrient supplies, and poor detoxifying ability. If your meal plan closely resembles the meal plans we recommend at the World’s Healthiest Foods, and you purchase many organically-grown foods, you are much more likely to have good nutrient supplies and good detoxifying ability, and are less likely to be putting your baby at risk. If your meal plan contains routine fast-food and take out, you are much less likely to have good nutrient supplies or good detoxifying ability, and more likely to be putting your baby at risk. Since the average U.S. adult consumes a diet that is much more like the fast food version than the World’s Healthiest Food version, the average U.S. adult would not be expected to have very good nutrient supplies or detoxifying ability, and risk here would be increased. Based on the food intake of the entire U.S. population, we would err on the side of caution and recommend that pregnant women and nursing mothers not consume mercury-contaminated fish at all, and wait to re-incorporate these fish back into their diet after their infants have stopped nursing. What makes this recommendation particularly difficult to make, however, is the value of fish (both fresh, frozen, and canned) for a particular kind of fat, omega 3 fatty acids, that U.S. adults and children consume far too little of, and that is found in helpful amounts in tuna and other cold water fish. Even canned tuna contains omega 3 fatty acids - about 200-300 milligram per 3.5 ounces - and these omega 3 fatty acids are critical for adult and infant health. Most all of us need more omega 3s! Taking canned tuna out of the diet for reasons of mercury contamination is a difficult decision for this reason. We still think that it's worth it for pregnant women and nursing mothers to take this step for safety's sake. However, we also believe it's critical to eat foods containing omega 3s! Use our Recipe Assistant to focus on omega 3 fatty acids as a nutrient, and click on yellowfin tuna as a food to exclude, and you’ll get a long list of fantastic tasting recipes that provide omega 3 fatty acids without relying on tuna to do so. If you are a pregnant women or nursing mother, you may even want to build your weekly menus around these high-omega recipes that avoid yellowfin tuna and other mercury-contaminated fish. And once you have finished nursing, you may want to reincorporate these foods back into your meal plan, making sure that you stay well-nourished and reap the benefits of the World's Healthiest Foods.

Fish Consumption During Pregnancy Improves Infants' Early Cognitive Development

Moderate consumption of uncontaminated fish during pregnancy and infancy may benefit cognitive development, suggests a study published in the July 2004 issue of Epidemiology.

(Since mercury is virtually everywhere in the environment, we interpret this to mean fish containing mercury in levels that do not exceed 500 ppb. This would eliminate shark, swordfish and marlin and limit tuna intake. We prefer to err on the side of safety and recommend avoiding tuna as well when pregnant or breastfeeding.)

In this study, researchers evaluated language and communication skills in 7,421 British children at 15 and 18 months of age. Infants whose mothers had consumed fish during pregnancy and whose diets, after the introduction of solid foods, had included fish, had higher developmental scores. For example, among children whose mothers had consumed fish 4 or more times per week, the average MacArthur Communicative Development Inventory score was 72 compared to 68 – 7% higher – among those whose mothers did not consume fish.

The latest UK Food Standards Agency (FSA) recommendations emphasize the health benefits of eating oily fish and provide guidelines for the maximum levels at which the health benefits clearly outweigh possible risks from another contaminant found in fish – dioxins and dioxin-like polychlorinated biphenyls (PCBs). According to the FSA, Women of childbearing age (including pregnant and breast-feeding women) and girls can safely eat up to 2-3 portions of oily fish per week – if they have not previously eaten more than this amount. Men, boys and women past childbearing age can safely eat up to 4 portions of oily fish per week. The full FSA report can be accessed from the FSA web site.

We still recommend choosing which oily fish you consume wisely. Tuna, unless known to be uncontaminated, and farmed salmon, which have been identified as having some of the highest levels of PCBs found anywhere in the world, should be avoided. (August 1, 2004)

Table 1

Species (Domestic Samples) Range (ppm) Average (ppm)
Catfish ND-0.16 ND
Cod ND-0.17 0.13
Crab ND-0.27 0.13
Flounder ND ND
Hake ND ND
Halibut 0.12-0.63 0.24
Pollack ND ND
Salmon (canned) ND ND
Salmon (fresh or frozen) ND ND
Shark 0.30-3.52 0.84
Swordfish 0.36-1.68 0.88
Tuna (canned) ND-0.34 0.20
Tuna (fresh or frozen) ND-0.76 0.38
Shark 0.30-3.52 0.84
Swordfish 0.36-1.68 0.88
Species (Imported Samples) Range (ppm) Average (ppm)
Pollack ND-0.78 0.84
Shark ND-0.70 0.36
Swordfish 0.80-1.61 0.86
Tuna (canned) ND-0.39 0.14
Tuna (fresh or frozen) ND-0.75 0.27

ND=not detected Source: FDA website (www.fda.gov)

Practical Tip

Lab tests measure methylmercury levels based on micrograms per liter of blood. The EPA safety threshold is 5.8 micrograms of methylmercury per liter. In an optimally healthy individual half of the mercury that is accumulated in the body is eliminated every 50 days. 99% of the mercury that we eat today will be gone within the year.

References

  • Andre, J.; Boudou, A.; Ribeyre, F., and Bernhard, M. Comparative study of mercury accumulation in dolphins (Stenella coeruleoalba) from French Atlantic and Mediterranean coasts. Sci Total Environ. 1991 May 15; 104(3):191-209.
  • Daniels JL, Longnecker MP, Rowland AS, Golding J; ALSPAC Study Team. University of Bristol Institute of Child Health. Fish intake during pregnancy and early cognitive development of offspring. Epidemiology. 2004 Jul;15(4):394-402.
  • Inasmasu, T.; Ogo, A.; Yanagawa, M.; Keshino, M.; Hirakoba, A.; Takahashi, K., and Ishinish, N. Mercury concentration change in human hair after the ingestion of canned tuna fish. Bull Environ Contam Toxicol. 1986 Oct; 37(4):475-81.
  • Louie, H. W.; Go, D.; Fedczina, M.; Judd, K., and Dalins, J. Digestion of food samples for total mercury determination. J Assoc Off Anal Chem. 1985 Sep-1985 Oct 31; 68(5):891-3.
  • Myers GJ, Davidson PW, Cox C et al. Prenatal methylmercury exposure from ocean fish consumption in the Seychelles child development study. Lancet. 2003 May 17;361(9370):1686-92.
  • Nakagawa, R.; Yumita, Y., and Hiromoto, M. Total mercury intake from fish and shellfish by Japanese people. Chemosphere. 1997 Dec; 35(12):2909-13.
  • Pilgrim, W.; Poissant, L., and Trip, L. The Northeast States and Eastern Canadian Provinces mercury study: a framework for action: summary of the Canadian chapter. Sci Total Environ. 2000 Oct 16; 261(1-3):177-84.
  • Storelli, M. M. and Marcotrigiano, G. O. Total mercury levels in muscle tissue of swordfish (Xiphias gladius) and bluefin tuna (Thunnus thynnus) from the Mediterranean Sea (Italy). J Food Prot. 2001 Jul; 64(7):1058-61.
  • Tollefson, L. and Cordle, F. Methylmercury in fish: a review of residue levels, fish consumption and regulatory action in the United States. Environ Health Perspect. 1986 Sep; 68:203-8.
  • Yakoo EM, Valente JG, Grattan L et al Low level methylmercury exposure affects neuropsychological function in adults. Environmental Health: A Global Access Science Source 2003 2:8.
  • Yess, N. J. U.S. Food and Drug Administration survey of methyl mercury in canned tuna. J AOAC Int. 1993 Jan-1993 Feb 28; 76(1):36-8.
  • Voegborlo RB, El-Methnani AM, and Abedin MZ. (1999). Mercury, cadmium and lead content and canned tuna fish. FOOD CHEMISTRY; 67 (4). 1999. 341-345.

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