Fish cleared as major mercury source

While fish has frequently been blamed for rising mercury levels in the human body, new research from the University of Bristol suggests that fish may not be the biggest contributor to mercury levels.

Results from the Children of the 90s study suggest that fish accounts for only 7% of mercury levels in the human body. In an analysis of 103 food and drink items consumed by 4484 women during pregnancy, researchers found that the 103 items together accounted for less than 17% of total mercury levels in the body.

Concerns about the negative effects of mercury on foetal 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, 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 1% 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.

“We were pleasantly surprised to find that fish contributes such a small amount (only 7%) to blood mercury levels,” said the report’s main author, Professor Jean Golding OBE.

“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.”