More evidence supports fish eating in pregnancy, but again finds mercury is to be avoided

Many of you will have noticed that nutritional information and advice can sometimes be widely contradictory and therefore very confusing. I usually mention this at the start of any talk I may give. One of examples I often cite is the general recommendation to eat a low-fat, high-carb diet, though on the other hand some argue for a diet relatively low in car (and maybe quite high in fat). Another example I quite often cite is the recommendation for women to consume oily fish in pregnancy for the so-called omega-3 fats that are supposedly good for the development of the foetal brain. On the other hand, some warn us to be wary of fish in pregnancy because it can be contaminated with mercury which can be toxic for the, err brain.

Scientists based at the Harvard Medical School and Harvard School for Public Health in Boston, USA, recently published a study which assessed the relationship between fish eating and mercury levels during pregnancy and the subsequent brain function in children who were the result of those pregnancies [1].

The scientists in this research assessed the fish intake of 341 women in the 2nd trimester (middle three months to you and I) of pregnancy. They also measured blood levels of mercury in these women. The children born to these women were assessed at the age of 3 years with tests of vocabulary and ‘visual motor abilities’.

Here’s what they found:

Consuming fish two or more times each week was associated with better visual motor abilities

Higher levels of mercury were associated with worsened outcomes with regard to both vocabulary and visual motor abilities

In other words, this study suggests that brain foetal development may be helped by the consumption of fish, but for the best results, women should avoid consuming fish contaminated with mercury. Armed with this sort of knowledge, women I think are in a better position to decide whether or not to eat fish during pregnancy, and if so, what forms of fish are likely to have the best ‘risk/benefit ratio’.

Further information and recommendations regarding omega-3 and fish intake can be found in previous blog posts here and here.


1. Oken E, et al. maternal fish intake during pregnancy, blood mercury levels, and child cognition at 3 years in a US cohort. Am J Epidem 2008 167(10):1171-1181


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