Fish increasingly contains toxic metals. A new study aims to discover the effects, writes Dick Ahlstrom.
It is a classic catch-22. Diets rich in fish are good for pregnant mothers and their growing babies, but fish can accumulate toxic metals such as mercury. Is it better to eat fish or avoid it during pregnancy?
A €13 million research collaboration involving the University of Ulster (UU) hopes to provide the answer to this question, and the result may already be favouring fish dinners.
"A lot of data says mothers should be eating fish during pregnancy and the benefit of this outweighs the risks," states Prof Sean Strain of the Northern Ireland Centre for Food and Health based at UU's Coleraine campus.
Strain will lead the university's team of nutritionists in a five-year study that also involves most EU states along with China, the US, Bangladesh and the Seychelles. The goal is to investigate the long-term effect of low levels of toxic metals such as mercury on the body.
"The focus of research in this study will not be on classical toxicity of high intakes, but rather on long-term, low-level exposures," says Prof Strain.
UU has a key role in the effort due to earlier US National Institutes of Health-funded work done in the Seychelles. That effort allowed the Coleraine team to assemble a cohort of 250 mothers and their children in the Seychelles who will now take part in this study.
The researchers want to conduct physiological and developmental tests on this group to assess whether there is a link between mercury exposures at background levels during gestation and any impacts after birth.
The Seychelles cohort are very important to the study given the high fish content of these islanders' diet. "The big advantage the Seychelles has is that they eat two servings of fish a day," says Prof Stain. Unfortunately, this also exposes them to toxic metals in the fish.
The researchers will be able to capture a highly reliable record of mercury intake over time from a most unusual source. Human hair as it grows takes up some of the available mercury, giving the researchers an individual tally of mercury levels in the diet.
"It gives a measure of mercury exposure. We have a history of the mercury," says Prof Stain. Hair grows at about a centimetre per month, so a single strand of hair will provide a record stretching back over months, far beyond a single pregnancy, depending on the hair style favoured by the mother.
The US researchers will measure this mercury while the UU group will study various blood parameters, says Prof Stain. Breast milk will also be assessed for metal content.
"The foetal brain is very sensitive to mercury compared to the adult brain," he says. The foetus is 10 times more sensitive to it and damage and even death can result if levels get too high.
If their early assumptions are correct, then the benefits of the fish nutrients may outweigh the impact of metal toxins. The local catch certainly has background levels of mercury, but the fish is also highly nutritious. "We believe that what the mothers are eating can counteract some of the toxicity of the mercury. The nutrients not only counter the mercury but also aid the development of the child," says Prof Stain.
"Data from child development tests that we carried out previously in the Seychelles suggest that the benefits of high fish consumption during pregnancy outweigh the risk of higher organic mercury exposure to the foetus," he says.
Stain heads the work at UU and he will be joined by Dr Julie Wallace, Dr Maxine Bonham and Dr Emeir Duffy. Five or six others will work in the Seychelles, taking blood samples and working with the study group.
The project looks at mercury but other toxic metals such as lead and cadmium are included in the study.