The UK’s Food Standards Agency (FSA) has advised pregnant and breastfeeding women, and women who intend to become pregnant, to limit their consumption of tuna to no more than two medium-size cans or one fresh tuna steak per week, because of the amount of mercury the fish contains.

The FSA said this precautionary advice is to protect against the small risk to the unborn child, and breast-fed babies, from mercury in certain fish. This is because mercury can harm an unborn child’s developing nervous system. Pregnant and breastfeeding women are also advised to avoid eating shark, swordfish and marlin.

Dr Andrew Wadge, acting director of food safety at the Food Standards Agency said: ‘It is unlikely that many pregnant or breastfeeding women eat more than the recommended amounts of these fish every week. But for any that currently do, it would be a sensible precaution to change their diets slightly. This will help protect the unborn child and the developing breastfed baby. When planning to have a baby and whilst pregnant or breastfeeding, women do need to take particular care of their health and that of their baby.’

This new advice on tuna does not apply to children or any other adults.

However, infants and children under 16 are still advised to avoid eating shark, swordfish and marlin. Shark, swordfish and marlin have levels of mercury approximately five to seven times higher than that of canned tuna and two to four times higher than that of fresh tuna. The Agency previously published advice on this issue on 10 May 2002.

The agency stressed that fish is a good source of high quality protein and other nutrients, and that oily fish can cut the risk of heart attacks. Because of these benefits, the FSA said that fish is also an important part of a balanced diet for pregnant women.

A survey of fish carried out by the FSA in 2002 revealed relatively high levels of mercury in some types of large predatory fish. This current advice is being issued following an extensive review by the independent Committee on Toxicity (COT) on the possible risks.

During this review, the COT compared levels of mercury found in fish against World Health Organisation safety guidelines for weekly intake of mercury. While the COT felt this limit was adequate to protect the general population, it was concerned that it may not be sufficiently protective for the developing foetus and breast-feeding baby because of the possible effects on the central nervous system. The COT concluded that, for these groups only, a more precautionary approach was required.

The new safety guideline for pregnant and breastfeeding women and women intending to become pregnant is almost five times lower than that for the general population.

The Food Standards Agency’s general advice on fish consumption is to eat two portions of fish a week, one of which should be oily, as part of a balanced and varied diet. This advice is based on findings that this level of fish consumption resulted in a significant reduction in the risk of heart attacks. On average, people in the UK eat only three-quarters of a portion of white fish and one quarter of a portion of oily fish a week.