Fish and mercury

Dr. Weeks’ Comment: This report is not helpful until we understand where the other 93% of the mercury come from… sometimes the difference between science and spin is imperceptible.  Might we know who funded this study? Smells fishy….

“…the question that is raised by these results: Where is the rest of the blood mercury coming from?..”

“…It has been estimated that 9.9 tons of mercury are deposited on the United Kingdom from the atmosphere each year…”


  • Background: Very high levels of prenatal maternal mercury have adverse effects on the developing fetal brain. It has been suggested that all possible sources of mercury should be avoided. However, although seafood is a known source of mercury, little is known about other dietary components that contribute to the overall levels of blood mercury.
    Conclusions: Although seafood is a source of dietary mercury, seafood appeared to explain a relatively small proportion of the variation in TBM in our UK study population. Our findings require confirmation, but suggest that limiting seafood intake during pregnancy may have a limited impact on prenatal blood mercury levels.


Concerns Over Mercury Levels in Fish May Be Unfounded

Sep. 30, 2013 ”” New research from the Children of the 90s study at the University of Bristol suggests that fish accounts for only seven per cent of mercury levels in the human body. In an analysis of 103 food and drink items consumed by 4,484 women during pregnancy, researchers found that the 103 items together accounted for less than 17 per cent of total mercury levels in the body.

Concerns about the negative effects of mercury on fetal development have led to official advice warning against eating too much fish during pregnancy. This new finding, published today in Environmental Health Perspectives, suggests that those guidelines may need to be reviewed.

Previous research by Children of the 90s has shown that eating fish during pregnancy has a positive effect on the IQ and eyesight of the developing child, when tested later in life. Exactly what causes this is not proven, but fish contains many beneficial components including iodine and omega-3 fatty acids.

After fish (white fish and oily fish) the foodstuffs associated with the highest mercury blood levels were herbal teas and alcohol, with wine having higher levels than beer. The herbal teas were an unexpected finding and possibly due to the fact that herbal teas can be contaminated with toxins.

Another surprise finding was that the women with the highest mercury levels tended to be older, have attended university, to be in professional or managerial jobs, to own their own home, and to be expecting their first child. Overall, however, fewer than one per cent of women had mercury levels higher than the maximum level recommended by the US National Research Council. There is no official safe level in the UK.

The authors conclude that advice to pregnant women to limit seafood intake is unlikely to reduce mercury levels substantially.

Speaking about the findings, the report’s main author, Professor Jean Golding OBE, said:

‘We were pleasantly surprised to find that fish contributes such a small amount (only seven per cent) to blood mercury levels. We have previously found that eating fish during pregnancy has many health benefits for both mother and child. We hope many more women will now consider eating more fish during pregnancy. It is important to stress, however, that pregnant women need a mixed balanced diet. They should include fish with other dietary components that are beneficial including fruit and vegetables.’




“…The diet is not the only contributor to blood mercury levels. Mercury can also be absorbed from water and air, and from nondietary products such as dental amalgam fillings, beauty products, social drugs such as cigarettes and alcohol, illicit drugs, and medications. Mercury vapor in the atmosphere is absorbed mainly through the respiratory tract (Holmes et al. 2009). Once absorbed, the mercury is widely distributed to fat-rich tissues, and is readily transferred across the placenta and blood brain barriers. Major sources include refuse incineration, fossil fuel combustion, and fungicides/pesticides (Hutton and Symon 1986). It has been estimated that 9.9 tons of mercury are deposited on the United Kingdom from the atmosphere each year (41% from sources in the United Kingdom, 33% from elsewhere in Europe, and 25% from other parts of the northern hemisphere) (Lee et al. 2001).



Although we confirmed that seafood was a major dietary contributor to blood mercury levels in our study population, estimated intakes of the three seafood items evaluated in our study (white fish, oily fish, and shellfish) accounted for only 8.75% of the estimated variation in log-transformed blood mercury concentrations. Of interest are the increased mercury levels in women who drank herbal teas, as well as confirmation of a “protective effect” of foods such as french fries, white bread, and milk, and the question that is raised by these results: Where is the rest of the blood mercury coming from?


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