A study published on October 3, 2019, in the International Journal of Epidemiology shows that babies whose mothers ate more seafood in the first three months of pregnancy showed greater attention capacity at eight years of age.
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Earlier research by the same scientists showed that children at five years of age, born in a population who typically ate a lot of fish, showed some improvement in cognitive processes, including thinking, memory, judgment, emotions and decision making, as well as a slightly reduced risk of autism spectrum disorders, when born to mothers in the highest percentile of seafood consumption, as compared to those born to mothers with the lowest percentile.
The current study included over 1,600 paired mothers and children drawn from the Spanish INMA Environment and Childhood Project, which studies pollutants in pregnancy and the effects they have on children. The mothers were regularly and frequently asked to complete questionnaires about the number of times they ate over 100 different types of foods, including seafood of various types. After the babies were born, the mothers also gave data about what the children ate, at age one, five and eight years.
When the children reached eight years of age, they were taken through the Attention Network Task (ANT), which is a computerized test of neurologic and psychological functioning intended to show the child’s capacity to be attentive to a given task. The ANT was evaluated mainly in terms of how many errors of omission were committed relative to the target stimuli, and how fast the child responded to the stimuli. These are typical outcomes that indicate how well a child can pay sustained and selective attention to a task.
Besides testing the attention capacity of the eight-year-old children, the study also explored the association between different types of seafood and the attention testing results. They found that when mothers ate all kinds of seafood in large amounts or plenty of fatty fish, their children performed very well on these tests. However, if canned tuna or shellfish were the primary sources of seafood consumption for the mother, children scored lower.
Fish consumption: good or bad?
Improvements in mental function with fish consumption have been theorized to be due to increased amounts of important nutrients such as long-chain polyunsaturated fatty acids, including ω-3 docosahexaenoic acid (DHA). The latter is considered a vital factor for normal growth and development of the fetal brain and nervous system. A typical Western diet contains little DHA apart from fatty sea fish. DHA is thought to be specially required for the early stages of neurodevelopment, and thus the consumption of seafood in the early part of pregnancy is beneficial for the brain growth of the fetus.
On the other hand, many researchers have expressed concern about the presence of methylmercury, organochlorine compounds and other neurotoxic substances in seafood. Thus, many health agencies have advised pregnant women to eat large fatty fish such as shark, king mackerel and swordfish, even though these contain high DHA levels.
On the other hand, there is not much solid evidence that the consumption of over 340g a week of seafood by the mother leads to fetal harm. This happens to be the upper limit allowable under US guidelines, though European Food Safety Authority recommendations envisage 1-4 servings of fish a week, which means 150-600 g. The task of teasing out the various interactions between DHA and methylmercury levels in the same fatty fish, and the combined effects on the child’s neurodevelopment, is quite difficult, which is one reason for the controversy.
Timing of seafood consumption: does it matter?
An earlier study covering almost 1,900 children at 14 months and about 1,600 five-year-olds showed the average consumption of seafood to be about 500 g/week. Mothers who ate large fatty fish in moderate amounts had children with better cognitive scores by about 2 points, and the positive association continued though it was slightly weaker, with seafood consumption in childhood. Many other studies show the same positive association of seafood consumption with many neuropsychiatric outcomes, including less hyperactivity and better attention capacity.
This could have indicated the importance of the timing of seafood consumption – early fetal life being a period of rapid and intense formation, differentiation and migration of brain neurons. The development of the complex nervous system includes processes such as the formation of synapses, or junctions between nerve cell projections to transmit nerve signals to other nerve cells, as well as the formation of the insulating and protective fatty myelin sheath around the nerve cell axons that form nerve fibers. DHA and another fatty acid called eicosapentaenoic acid (EPA) are both omega-3 fatty acids that are intimately associated with such developmental processes – and both are derived from seafood, in most people.
The researchers also tried to understand how genetic factors affected the functioning of PUFAs in the body. They looked at gene variations in which a single nucleotide was altered, called single nucleotide polymorphisms (SNPs), in relation to how seafood affected the child’s attention capacity. They concluded that certain SNPs help the body to use the PUFAs more effectively, which increases the child’s neurodevelopment as shown by higher attention scores. Other SNPs affect the PUFA metabolism negatively, and in these children especially, seafood could bridge this gap if consumed in early pregnancy.
Julvez points out,
Children with, for example, the rs1260326 CC genotype – which has been associated with lower PUFA levels – had worse attention scores if their mothers had not eaten much seafood during pregnancy. But their outcomes improved if their mothers consumed more seafood.”
Researcher Jordi Júlvez
The importance of a 2-point increase in a child’s score on cognitive testing reflects a significant increase at the population level, shifting the number of children with low intellectual ability to the lower side. As a result, the researchers carried on their study with another one, this time focusing on children at eight years of age.
The consumption of seafood during the first trimester of pregnancy had a greater effect on children's attention capacity than the consumption of seafood later in pregnancy or at five years of age, by which time some neurodevelopment processes have already been completed.”
The consumption of food rich in DHA and other PUFAs in pregnancy by the mother is thus essential for the continued neurological and psychological development of the child after birth as they modulate the brain’s growth. Attention is both a basic and complex trait that is vital to learning since it underlies the formation of memory. Moreover, school-age children are commonly diagnosed with attention-deficit hyperactivity disorder, which is the reason why the behavioral trait of attention was the focus of the current study.
So does this mean all mothers should go ahead and eat a lot of seafood? Unfortunately, some research has indicated a possible link between fish consumption in pregnancy and obesity in childhood, with high blood pressure. There is, therefore, a need to delve more deeply into this topic to decide what type of, and how much, seafood may be eaten safely and beneficially in pregnancy.
Maternal consumption of seafood in pregnancy and child neuropsychological development: a longitudinal study based on a population with high consumption levels. Jordi Julvez et al. American Journal of Epidemiology, Volume 183, Issue 3, 1 February 2016, Pages 169–182. https://doi.org/10.1093/aje/kwv195.