Pregnancy is a time when the mother’s diet becomes essential not only for reasons of proper nutrition but to avoid harm to or enhance the development of the child. Now a new study published in the journal JAMA Network Open in March 2020 shows that mothers who ate one to three servings of fish a week while they were pregnant gave birth to children with a better metabolic profile compared to those mothers who ate little or no fish at this time.
The potential for mercury toxicity, which can cause fetal neurological damage, has held back pregnant women from eating many types of fish. The balance between the risk caused by mercury and the benefit in nutritional terms from fish intake in pregnancy is mostly unknown, and this was the focus of the study.
What are the nutrients in fish? For one, fish contains a lot of polyunsaturated long-chain omega-3 fatty acids, a type of compound that is important in the physical development of the fetus. Some sea fish, however, like the swordfish, shark, and mackerel, have been proved to contain high mercury levels, and this, in turn, causes long-term damage to the developing brain. Mercury is also found in soil, water, air, and plants.
The researchers analyzed 805 mother-child pairs in 5 European countries, as part of the HELIX study, in which pregnant women are followed until the children are born, at which point the infants are also included in the research. The average maternal age was 31 years. Most were white, and about half were carrying their first pregnancy. The average woman in this study ate fish 3.7 times a week.
The pregnant women were surveyed and asked about how much fish they ate in an average week, and their blood mercury levels were tested.
After 6-12 years, the children born to the same women were examined clinically, and several measurements were also taken – the waist circumference, the blood pressure, high-density lipoprotein cholesterol, triglycerides, and insulin. These measurements were used to calculate a metabolic syndrome score.
The study found that children born to pregnant women who consumed fish one to three times a week vs. those born to mothers who ate less than one serving of fish a week had a better metabolic function, as assessed by the metabolic syndrome scores.
However, the researchers also observed a higher score (implying an impaired metabolic profile) for women who ate more than three servings of fish a week. Mercury levels were higher in women who ate moderate to high levels of fish.
Researcher Leda Chatzi puts the matter in perspective, based on the study findings: “Fish is an important source of nutrients, and its consumption should not be avoided. But pregnant women should stick to one to three servings of fish a week as recommended, and not eat more, because of the potential contamination of fish by mercury and other persistent organic pollutants.”
The most significant benefit in terms of lowering of the metabolic syndrome score is linked to the combination of moderate fish intake and low mercury levels. Higher maternal intake of fish was associated inversely with waist circumference and insulin levels.
The explanation offered by researcher Nikos Stratakis is the presence of pollutants in fish, which can cross the limit of harm if the number of servings is excessive. In his words, “It is possible that when women eat fish more than three times a week, that pollutant exposure may counterbalance the beneficial effects of fish consumption seen at lower intake levels.”
Notably, a higher concentration of mercury in the woman’s blood was linked to a higher score in the child. However, the study also looked at certain cytokines and adipokines in the child’s blood in relation to fish consumption. Cytokines are signaling chemicals released by the inflammatory cells in the body, while adipokines are similar compounds released by fat cells.
The aim of the researchers was to detect inflammation in the body because this is in part related to the metabolic syndrome. Against the background of fish intake, they found that consuming more fish in pregnancy was linked to lower levels of this inflammation-producing or to enhance chemicals in the body.
The authors say this is the first time that the association of fish consumption by pregnant women with better metabolic health in the child has been explained by the reduction in the biomarkers of the inflammatory process.
The next step is to examine how consuming different types of fish affects the child since each has its own nutritional and mercury content. They aim to follow up with the child until 14 or 15 years.
Stratakis N, Conti DV, Borras E, et al. Association of Fish Consumption and Mercury Exposure During Pregnancy With Metabolic Health and Inflammatory Biomarkers in Children. JAMA Netw Open. 2020;3(3):e201007. doi:10.1001/jamanetworkopen.2020.1007