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.'
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The paper, Golding J et al, 'Dietary predictors of maternal prenatal blood mercury levels in the ALSPAC birth cohort study is published today [1 October 2013] in the journal Environmental Health Perspectives, DOI: 10.1289/ehp.1206115