Experts reveal how many tins of tuna is safe to eat a week
Updated: 09:34 GMT, 1 November 2024
Earlier this week, concerns were raised about the safety of tinned tuna, after tests on 150 cans purchased in five countries found half contained in excess of the recommended amount of the toxin mercury.
The study, by French researchers, found that all tins studied — including some bought in the UK — contained some of the metal, which, in large quantities, can harm brain health and has been linked to cancer.
In fact, the NHS advises pregnant women should not eat more than two tuna steaks or four tins a week due to the risk of harm to an unborn baby's brain.
And it's not just tuna that contains mercury; in fact all fish does, with some types, like swordfish, packed with particularly large amounts.
So how much is safe for us to eat?
Firstly, whether the fish is tinned or not makes little difference.
The majority of the mercury put into the atmosphere from natural and human causes, such as burning coal, ends up in the ocean where some is converted by tiny organisms to a toxic compound known as methylmercury.
This methylmercury works its way up the food chain and accumulates in top predators in high concentrations.
As tuna — and other predators or longer-living species like sharks or swordfish — are higher up the food chain, they eat smaller fish and accumulate more mercury over time.
Exposure to methylmercury may damage the kidneys and nervous system, trigger issues with vision and raise the risk of cardiovascular disease.
According to the World Health Organisation, mercury can also cause neurological and behavioural disorders if it is inhaled, eaten or if the skin comes into contact with it.
Symptoms include tremors, insomnia, memory loss, headaches and cognitive and motor dysfunction.
In very high doses, studies have found that some forms of mercury have triggered the development in several types of tumors in rats and mice.