The USDA issues Dietary Guidelines for Americans every five years, and the agency is gathering expert input for the 2020-2025 update.
As part of that process, the USDA’s Dietary Guidelines Advisory Committee (DGAC) invites public comments on dozens of questions it posted online.
Two of the DGAC’s questions related to the effects of seafood on children and adolescents:
- What is the relationship between seafood consumption during pregnancy and lactation and the neurocognitive development of the infant?
- What is the relationship between seafood consumption during childhood and adolescence (up to 18 years of age) and neurocognitive development?
To answer those questions, 13 widely recognized experts in this field collaborated to review the available evidence, and submit their conclusions to the DGAC's Dietary Fat & Seafood subcommittee, whose members devised those two key questions.
The new evidence review covered all 44 studies published before and since the most recent prior review. Those studies involved 102,944 mother-child pairs (29 studies) and 25,031 children (15 studies), which adds to the credibility of the authors’ conclusions.
Importantly, the authors of the new review had no conflicts of interest, and their study adhered to the USDA's rigorous criteria for Nutrition Evidence Systematic Reviews.
Comprehensive evidence review finds seafood safe and beneficial
Like all prior evidence reviews, the expert committee’s report concluded that maternal and childhood diets higher in seafood deliver clear benefits for infant and adolescent brain development (Hibbeln JR et al. 2019).
These are highlights of the expert committee’s evidence review:
- Most of the mother-child studies (24 of 29) inked higher seafood intake among mothers to beneficial neurocognitive (brain performance) outcomes on some or all the tests administered to their children, who ranged in age from three days to 17 years.
- Children gained an average of 7.7 IQ (intelligence quotient) points when their moms ate seafood during pregnancy, compared with children born to mothers who ate no seafood. The size of IQ benefits ranged from 5.6 to 9.5 points.
- Higher seafood consumption was linked to better outcomes on verbal, visual, and motor skill development, as well as scholastic achievement.
- Four of the 24 mother-child studies compared seafood consumption with the risk for developing hyperactivity or ADHD, and one of those studies found that children of mothers who did not eat fatty, omega-3-rich seafood were nearly three times more likely to be diagnosed with hyperactivity.
- Benefits to children’s neurocognitive development appeared at the lowest maternal seafood intakes during pregnancy (one serving per week), and no adverse developmental effects were detected even when a mother consumed up to 100 ounces (about 25 servings) per week.
- Seafood consumption was not linked to negative brain development outcomes in any of the studies, which indicates that there may be no upper limit to seafood’s benefits for brain development.
“There is a lost opportunity for IQ when mothers are not eating enough seafood,” said the lead author of the new evidence review, Capt. Joseph Hibbeln, M.D., Acting Chief, National Institute on Alcohol Abuse and Alcoholism.
Dr. Hibbeln co-authored two recent, related studies, both of which found only benefits for children’s brain development when their pregnant mothers ate seafood, and no risk from the resulting higher intakes of methylmercury (Golding J et al. 2017; Hibbeln J et al. 2018).
“The risk is not eating enough seafood — the benefits are substantial for the development of baby brains, eyes and overall nervous system,” added study co-author J. Thomas Brenna, Ph.D., who is a member of the 2015-2020 Dietary Guidelines Advisory Committee.
As Dr. Brenna and his co-authors wrote, “Moderate and consistent evidence indicates that consumption of a wide range of amounts and types of commercially available seafood during pregnancy is associated with improved neurocognitive development of offspring as compared to eating no seafood. This evidence does not meet the criteria for “strong evidence” only due to a paucity of randomized controlled trials that may not be ethical or feasible to conduct for pregnancy.”
Critically, as they wrote, “No net adverse neurocognitive outcomes were reported among offspring at the highest ranges of seafood intakes despite associated increases in mercury exposures.” And, as they said, “… there is some evidence that dark/oily seafood may be more beneficial”.
That apparent brain-development advantage for oily (fatty) fish is likely attributable to the fact that — in addition to vitamin D — fatty species like salmon, albacore tuna, sardines, and sablefish are especially rich in omega-3 fatty acids (DHA and EPA), which are critical brain nutrients and anti-inflammatory agents.
The researchers speculated that the clearly positive outcomes of higher seafood consumption flow from the fact that — in addition to protein — it provides nutrients known to promote optimal brain development and function, including omega-3 fatty acids, trace minerals like iodine and selenium, and vitamins B-6, B-12, and D.
To read some of our past coverage of this issue, see Benefits of Fish to Kids Found to Outweigh Risks, Feds Advise Kids and Pregnant Women to Eat More Fish, FDA Analysis Supports More Fish for Moms and Kids, and Findings Verify Safety and Value of Higher Maternal Fish Intake. You'll find more information on the Healthy Mom & Baby page of our website.
Why would most (not all) ocean fish be safe and beneficial despite mercury?
The best available studies of populations where pregnant mothers and children eat copious amounts of seafood — such as the Seychelles Islands — have not detected any significant harm from that dietary habit.
Methylmercury is toxic largely because it binds to selenium, which the body needs as a component of key internal antioxidants called selenoenzymes (e.g., glutathione peroxidase and thioredoxin reductase). This may help expain why methylmercury disrupts nerve transmission/conductivity and promotes “excitotoxicity” while killing the brain’s neurons and their supporting glial cells.
As researchers from Northeastern University and the University of North Dakota explained, “Selenoenzymes … have roles in preventing and reversing oxidative damage in brain and endocrine tissues. Since the brain’s high rate of oxygen consumption is accompanied by high ROS [free radical] production, selenoenzyme activities are particularly important in this tissue.” (Raymond LJ et al. 2014)
Accordingly, one credible but as yet unproven hypothesis proposes that most ocean fish are safe to eat because they contain substantially more selenium than mercury. Thus, they provide enough selenium to maintain healthy levels of selenoenzymes, even though their methylmercury depletes some of the body’s selenium stores.
Another hypothesis for the documented safety of almost all ocean fish is that their package of brain-enhancing nutrients outweighs the negative effects of mercury. That idea fits with the fact that children’s brain development benefits most when their pregnant mothers eat lower-mercury fish species, and least when their mothers eat higher-mercury species (Oken E et al. 2008; Mahaffey KR et al. 2011).
Regardless of the reason, almost all ocean fish — except the few species that are higher in mercury than selenium (e.g., shark, swordfish, Gulf tilefish, and king mackerel) — appear very safe to eat.
Indeed, the only studies that have detected some harm to children’s brain development involved populations that ate seafood high in man-made contaminants such as PCBs, or seafood that was high in methylmercury and low in selenium.
Those studies were conducted in the Faroe Islands, where people eat lots of pilot whale — which is high in mercury and PCBs and low in selenium — and New Zealand, where people eat lots of shark, which is high in mercury but low in selenium.
For more on this topic, see Video Explains Seafood's Clean Safety Record and its links to related articles, including Most Fish Rank as Very Safe on New, Selenium-Based Standard.
- European Food Safety Authority. Scientific Opinion on health benefits of seafood (fish and shellfish) consumption in relation to health risks associated with exposure to methylmercury. EFSA Journal. 2014; 12: 3761. Accessed at https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/j.efsa.2014.376
- FAO/WHO. Report of the Joint FAO/WHO Expert Consultation on the Risks and Benefits of Fish Consumption. Rome, 25–29January 2010., (2011). Accessed atwww.fao.org/docrep/014/ba0136e/ba0136e00.pdf.
- Food and Drug Administration USA. Quantitative Assessment of the Net Effects on Fetal Neurodevelopment from Eating Commercial Fish (As Measured by IQ and also by Early Age Verbal Development in Children), (2014). Accessed at https://www.fda.gov/food/metals/quantitative-assessment-net-effects-fetal-neurodevelopment-eating-commercial-fish-measured-iq-and.
- Gilman CL, Soon R, Sauvage L, Ralston NV, Berry MJ. Umbilical cord blood and placental mercury, selenium and selenoprotein expression in relation to maternal fish consumption. J Trace Elem Med Biol. 2015 Apr;30:17-24. doi: 10.1016/j.jtemb.2015.01.006. Epub 2015 Jan 21.
- Golding J, Hibbeln JR, Gregory SM, Iles-Caven Y, Emond A, Taylor CM. Maternal prenatal blood mercury is not adversely associated with offspring IQ at 8 years provided the mother eats fish: A British prebirth cohort study. Int J Hyg Environ Health. 2017 Oct;220(7):1161-1167. doi: 10.1016/j.ijheh.2017.07.004. Epub 2017 Jul 17.
- Government of Canada, Prenatal Nutrition Guidelines for Health Professionals – Fish and Omega-3 fatty acids2009. Accessed at https://www.canada.ca/en/health-canada/services/publications/food-nutrition/prenatal-nutrition-guidelines-health-professionals-fish-omega-3-fatty-acids-2009.html (last accessed 7/9/2019).
- Hibbeln J, Gregory S, Iles-Caven Y, Taylor CM, Emond A, Golding J. Total mercury exposure in early pregnancy has no adverse association with scholastic ability of the offspring particularly if the mother eats fish. Environ Int. 2018 Jul;116:108-115. doi: 10.1016/j.envint.2018.03.024. Epub 2018 Apr 14.
- Hibbeln JR, Spiller P, Brenna JT, et al. Relationships between seafood consumption during pregnancy and childhood and neurocognitive development: two systematic reviews. Prostaglandins, Leukotrienes and Essential Fatty Acids (PLEFA) (2019). DOI: https://doi.org/10.1016/j.plefa.2019.10.002
- Mahaffey KR, Sunderland EM, Chan HM, Choi AL, Grandjean P, Mariën K, Oken E, Sakamoto M, Schoeny R, Weihe P, Yan CH, Yasutake A. Balancing the benefits of n-3 polyunsaturated fatty acids and the risks of methylmercury exposure from fish consumption. Nutr Rev. 2011 Sep;69(9):493-508. doi: 10.1111/j.1753-4887.2011.00415.x. Review.
- Nesheim MC, Yaktine A. Seafood Choices Balancing Benefits and Risks. (Available at) (Last accessed 8/8/19)Instiute of Medicine of the National Academy, Washington, D.C.; 2007. Accessed at http://www.nationalacademies.org/hmd/Reports/2006/Seafood-Choices-Balancing-Benefits-and-Risks.aspx
- Oken E, Østerdal ML, Gillman MW, Knudsen VK, Halldorsson TI, Strøm M, Bellinger DC, Hadders-Algra M, Michaelsen KF, Olsen SF. Associations of maternal fish intake during pregnancy and breastfeeding duration with attainment of developmental milestones in early childhood: a study from the Danish National Birth Cohort. Am J Clin Nutr. 2008 Sep;88(3):789-96.
- 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.
- Ralston NV, Raymond LJ. Dietary selenium's protective effects against methylmercury toxicity. Toxicology. 2010 Nov 28;278(1):112-23. doi: 10.1016/j.tox.2010.06.004. Epub 2010 Jun 16. Review.
- Ralston NVC, Ralston CR, Raymond LJ. Selenium Health Benefit Values: Updated Criteria for Mercury Risk Assessments. Biol Trace Elem Res. 2016 Jun;171(2):262-269. doi: 10.1007/s12011-015-0516-z. Epub 2015 Oct 13.
- Ralston NVC, Raymond LJ. Mercury's neurotoxicity is characterized by its disruption of selenium biochemistry. Biochim Biophys Acta Gen Subj. 2018 May 9. pii: S0304-4165(18)30141-7. doi: 10.1016/j.bbagen.2018.05.009. [Epub ahead of print] Review.
- Raymond LJ, Deth RC, Ralston NV. Potential Role of Selenoenzymes and Antioxidant Metabolism in relation to Autism Etiology and Pathology. Autism Res Treat. 2014;2014:164938. doi: 10.1155/2014/164938. Epub 2014 Mar 5. Review.
- Spiller P, Hibbeln JR, Myers G et al. An abundance of seafood consumption studies presents new opportunities to evaluate effects on neurocognitive development. Prostaglandins, Leukotrienes and Essential Fatty Acids (PLEFA) (2019). DOI: https://doi.org/10.1016/j.plefa.2019.10.001
- Usuki F, Yamashita A, Fujimura M. Post-transcriptional defects of antioxidant selenoenzymes cause oxidative stress under methylmercury exposure. J Biol Chem. 2011 Feb 25;286(8):6641-9. doi: 10.1074/jbc.M110.168872. Epub 2010 Nov 24.