Should women eat oily fish in pregnancy – yes or no?!

The home page of asks: Ever noticed how health advice, especially natural health advice, can seem to flick-flack from one extreme to another? Well, another example of the way health advice can seemingly blow in the wind came about this week when pregnant women were advised to be on ‘oily fish alert’. For some time now, oily fish has been advocated in pregnancy because the so-called omega-3 fats these contain are believed to help in the healthy development of the foetus, particularly with regard to the brain and visual ability.

Recently, however, the journal Environmental Health Perspectives published a study in which women who had their babies at least two weeks early were found to have raised levels of mercury in their bodies. The relevance of this to fish-eating is that certain fish are a source of mercury. Consistent with this was the finding in this particular study that found the women with high levels of mercury were also tended to eat more oily fish, particularly canned fish.

Actually, more oily fish such as salmon, trout, mackerel, herring and sardine, do not tend to be contaminated with mercury. The worse offenders are ‘big’ fish such as marlin, swordfish and tuna. It is interesting that it was canned fish that was recently been associated with higher body mercury levels, as this may be explained by the fact that canned fish, particularly in America where the study was done, usually means tuna.

This is not the only reason why I think women should avoid canned tuna in pregnancy ” the fish is de-fatted prior to canning and although it is generally regarded as ‘oily’, the fact is it offer very little omega-3 compared to truly oily fish like salmon, mackerel and sardine.

I have attached here an article which looks at this issue of mercury in fish and it’s relevance to pregnancy in more depth.


1. Environmental Health Perspectives, DOI: 10.1289/ehp.9329

Observer Column – 9th March 2003

Barely a week seems to go by without the publication of a report or study extolling the health-boosting virtues of fish. Good news about fish abounds, it appears, so it’s no surprise that many of us are making a concerted effort to eat more of it. However, recent news that some fish species, including tuna, may be contaminated with mercury appears to have sent quite a ripple of disquiet amongst fish lovers. Because mercury has the potential to damage the nervous system of developing foetuses and small children, women who are pregnant, planning pregnancy or breast feeding have been advised to limit their consumption of tuna and to exclude some other types of fish altogether. After years of riding a tide of positive publicity, could it be that the chips are up for fish?

Mercury’s presence in the sea is the result of its natural release from the earth’s crust and industrial pollution. Not surprisingly, this metal has the propensity to makes its way from seawater into the fish that inhabit it. However, not all species of fish are as prone to mercury contamination as others. Through a phenomenon known as bioconcentration, mercury concentrations tend to increase the higher up the food chain you go. Basically, what this means is that the bigger the fish, the more tainted it is likely to be. Tuna, a firm favourite in this country in both fresh and canned forms, is one big fish well known to be prone to pollution with mercury, as is whale, marlin, swordfish and shark.

Research performed over the last 20 years has suggested that eating fish tainted with mercury can interfere with the neurological development of foetuses and small children. Some of the evidence for this has come from a study performed in Faroe Islanders, the diet of whom is traditionally rich in whale meat contaminated with mercury. Researchers have discovered that increasing levels of mercury in this population are associated with impairment in language, attention, memory and movement in children. As a result of this and other research, the Food Standards Agency here in the UK has recommended that women who are pregnant, planning pregnancy or breast feeding should limit their consumption of tuna to two medium-sized cans or one fresh tuna steak per week. They have also recommended complete abstinence from shark, marlin and swordfish for these women and all children under the age of 16.

My personal feelings that avoiding fish likely to be contaminated with mercury makes good sense. However, let us not forget that the omega-3 fats found in certain species of fish are known to promote health, and actually help neurological development in the growing foetus and during childhood. As it happens, while tuna is often classified as an oily fish, tests reveal it’s omega-3 content is actually really quite low. The best ploy, I think, is to shift emphasis away from tuna, towards fish that offer more in the way of healthy omega-3 fats, and less in the way of mercury. For those looking for a direct swap, I recommend salmon, either fresh or in tinned form. Other options include trout, mackerel and herring. While tuna may be of the menu for many, the good news is there’s plenty more fish in the sea.

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