If you’re pregnant or trying to conceive, you’ve probably been advised not to eat too much seafood to protect your baby from evil mercury. But using data from the Children of the 90s study, scientists from Bristol University now suggest that the warning may be overrated and that women can safely increase their consumption of oily fish.
The concerns with mercury
Since the metal can be readily absorbed by fat-rich tissues, it can easily cross the placenta and reach the foetus’ brain and nervous system where it can hamper development. Mercury exposure has also been linked to fertility issues and miscarriage.
Fish: Definitely a friend
It is well established that seafood is the richest source of the long-chain omega-3s DHA and EPA –these fatty acids are essential during pregnancy as they are needed for optimal foetal brain and nervous system development. Previous studies have linked prenatal DHA consumption to improved behaviour, visual recognition, IQ and language skills in infancy. Plus omega-3s can also protect you from increased anxiety during pregnancy and cardiovascular complications later on.
The researchers collected diet and sociodemographic information from 4,484 pregnant women who were previously enrolled in the ALSPAC study. Blood samples were sent to the Centre for Disease Control where they were analysed for total mercury content.
“We were pleasantly surprised to find that fish contributes such a small amount, only 7 per cent, to blood mercury levels,” reported study lead author Professor 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,” Professor Golding said.
The team also discovered that:
- Food and drink accounted for 17% of mercury levels in the women’s blood.
- After white and oily fish, herbal teas and alcohol were found to have the highest mercury levels.
- Wine appeared to contain more mercury than beer.
- Less than 1% of the women showed mercury levels above the maximum recommended by the US National Research Council – there are no official safe levels in the UK.
Limiting seafood is unlikely to significantly reduce your mercury levels. The scientists explain that diet is not the sole contributor to blood mercury levels – you can also absorb mercury from water, air, dental amalgam fillings, cosmetic products, cigarettes, alcohol, illegal drugs and medications.
So, should you eat more fish?
The Food Standard Agency maintains the current guidelines regarding fish consumption during pregnancy. A spokesman told the Daily Mail that ‘most people do not eat enough fish. However, children, pregnant women and women who are trying to get pregnant should not eat shark, marlin or swordfish. If you are trying for a baby or are pregnant, you should have no more than four cans of tuna a week. Mackerel, sardines, salmon and trout should not be eaten more than twice a week.’
Golding et al (2013) Dietary predictors of maternal prenatal blood mercury levels in the ALSPAC birth cohort study. Environ Health Perspect. 121(10):1214-1218.