Concerns about the risks of mercury to children have led to official advice to limit fish intake during pregnancy.
In 2001, the U.S. EPA and FDA issued joint guidelines for children and pregnant/nursing mothers.
The agencies recommend limiting tuna consumption, and warned against eating any of four higher-mercury species: shark, swordfish, tilefish, and king mackerel (our Portuguese mackerel is a different, smaller, very-low-mercury species).
Contradicting those mercury concerns, a large 2007 British study found that children benefited when they and their pregnant mothers ate more seafood than average.
Since then, several other studies have allayed fears about possible mercury-related effects of seafood on children, and/or found benefits to higher fish intakes (Oken E et al. 2008; Lederman SA et al. 2008; Ramón R et al. 2009; Drouillet-Pinard P et al. 2010; Deroma L et al. 2013).
In part, the safety of almost all seafood – except a very few species like shark, and marine mammals (whales and seals) – stems from the role that selenium plays.
Ocean fish are by far the richest sources of iodine, selenium, and omega-3 fatty acids, which are essential to brain, immune-system, and eye development.
Now, a study from U.S. and British researchers offers more reassurance about the safety of virtually all seafood.
Concerns about fish as a major mercury source appear unfounded
The new study comes from scientists at the U.S. National Institutes of health, and Britain's University of Bristol (Golding J et al. 2013).
Based at the University of Bristol, the Avon Longitudinal Study of Parents and Children (ALSPAC
) – also known as Children of the 90s – has been monitoring more than 14,000 British children since birth.
Previous ALSPAC research showed that eating fish during pregnancy improves the IQ and eyesight of a developing child, when tested later in life.
For their new study, the ALSPAC researchers analysed 103 food and drink products consumed by 4,484 women during pregnancy.
They found that together, those food and drink products accounted for less than 17 percent of total mercury in the mothers' bodies.
And – contradicting an assumption common to regulators and consumers – fish accounted for only seven percent of the mercury in the mothers' bodies.
After fish (lean and fatty) the foods associated with the highest mercury blood levels were herbal teas and alcohol, with wine having higher levels than beer.
The authors conclude that advice to pregnant women to limit seafood intake is unlikely to reduce mercury levels substantially.
Women with the highest mercury levels tended to be older, have attended university, to be in professional or managerial jobs, to own their own home, and to be expecting their first child.
Overall, however, less than one percent of women had mercury levels higher than the level recommended by the US National Research Council.
Lead author Professor Jean Golding OBE, made several comments about the findings (ALSPAC 2013):
- “We were pleasantly surprised to find that fish contributes such a small amount (only seven percent) to blood mercury levels.”
- “We have previously found that eating fish during pregnancy has many health benefits for both mother and child.”
- “We hope many more women will now consider eating more fish during pregnancy. It is important to stress, however, that pregnant women need a mixed balanced diet. They should include fish with other dietary components that are beneficial including fruit and vegetables.”
Together with strong evidence that the selenium in ocean fish renders its mercury harmless – and that high maternal intake of ocean fish causes no harm – this new finding suggests that the EPA-FDA guidelines should be revised.
Funding for the study was provided by the National Seafood Inspection Laboratory of the US National Oceanic and Atmospheric Administration (NOAA).
Diet is only one source of mercury
Mercury can also be absorbed from water and air and is present in dental amalgam fillings, beauty products, legal drugs (like alcohol and tobacco), illegal drugs, and some medications.
Major sources of mercury include refuse incineration, coal-fired power plants, fungicides, and pesticides.
- Golding J, Steer CD, Hibbeln JR, Emmett PM, Lowery T, Jones R. Dietary Predictors of Maternal Prenatal Blood Mercury Levels in the ALSPAC Birth Cohort Study. Environ Health Perspect. 2013 Oct;121(10):1214-1218. Epub 2013 Jun 26. doi.org/10.1289/ehp.1206115
- ALSPAC. Concerns over mercury levels in fish may be unfounded. October 1, 2013. Accessed at http://www.bristol.ac.uk/alspac/news/2013/191.html
- Deroma L, Parpinel M, Tognin V, Channoufi L, Tratnik J, Horvat M, Valent F, Barbone F. Neuropsychological assessment at school-age and prenatal low-level exposure to mercury through fish consumption in an Italian birth cohort living near a contaminated site. Int J Hyg Environ Health. 2013 Jul;216(4):486-93. doi: 10.1016/j.ijheh.2013.02.004. Epub 2013 Mar 6.
- Drouillet-Pinard P, Huel G, Slama R, Forhan A, Sahuquillo J, Goua V, Thiébaugeorges O, Foliguet B, Magnin G, Kaminski M, Cordier S, Charles MA. Prenatal mercury contamination: relationship with maternal seafood consumption during pregnancy and fetal growth in the 'EDEN mother-child' cohort. Br J Nutr. 2010 Oct;104(8):1096-100. doi: 10.1017/S0007114510001947. Epub 2010 May 21.
- Lederman SA, Jones RL, Caldwell KL, Rauh V, Sheets SE, Tang D, Viswanathan S, Becker M, Stein JL, Wang RY, Perera FP. Relation between cord blood mercury levels and early child development in a World Trade Center cohort. Environ Health Perspect. 2008 Aug;116(8):1085-91. doi: 10.1289/ehp.10831.
- Ramón R, Ballester F, Aguinagalde X, Amurrio A, Vioque J, Lacasaña M, Rebagliato M, Murcia M, Iñiguez C. Fish consumption during pregnancy, prenatal mercury exposure, and anthropometric measures at birth in a prospective mother-infant cohort study in Spain. Am J Clin Nutr. 2009 Oct;90(4):1047-55. doi: 10.3945/ajcn.2009.27944. Epub 2009 Aug 26.
- Oken E, Radesky JS, Wright RO, Bellinger DC, Amarasiriwardena CJ, Kleinman KP, Hu H, Gillman MW. Maternal fish intake during pregnancy, blood mercury levels, and child cognition at age 3 years in a US cohort. Am J Epidemiol. 2008 May 15;167(10):1171-81. doi: 10.1093/aje/kwn034. Epub 2008 Mar 18.
- Pearson H. Children of the 90s: Coming of age. April 11, 2012. Nature. Accessed at http://www.nature.com/news/children-of-the-90s-coming-of-age-1.10396