- Swordfish and shark both are known to contain high levels of the metal mercury
- This is linked to motor neurone disease – which Stephen Hawking suffers from
- The condition attacks nerves that control movement so muscles no longer work
- Regular fish eaters who consumed mercury were twice as likely to have MND
It’s an exotic ingredient used in trendy recipes by Nigella Lawson and Jamie Oliver, but eating swordfish may raise the risk of being diagnosed with motor neurone disease.
Both swordfish and shark meat contain high levels of mercury, which have been linked to the rare condition.
The progressive disease, which famously affects physicist Stephen Hawking, attacks nerves that control movement so muscles no longer work.
A study by US researchers found that regular fish eaters whose mercury consumption registered in the top 25 per cent were twice as likely to have MND.
Both swordfish and shark meat contain high levels of mercury, which have been linked to the rare condition made famous by Stephen Hawking
This was based on a survey of their seafood consumption, and on their nail clippings which were tested for mercury.
Swordfish and shark are believed to have more mercury in their system, as they are at the top of the food chain and eat smaller fish which accumulate the toxic metal.
It may contribute to MND, which kills six people a day in Britain, by damaging the way the cells work within the body.
The NHS already advises adults to eat only one portion of shark or swordfish a week, with children and pregnant women told to avoid them altogether.
The Motor Neurone Disease Association described the research as presenting an ‘intriguing theory’ on these types of fish, but said mercury would cause only a small risk for the disease.
The researchers at Dartmouth College studied 518 people, 294 with motor neurone disease and 224 without, asking them how much fish and seafood they ate.
Regular fish eaters whose mercury consumption registered in the top 25 per cent were twice as likely to have MND, a study found
Annual exposure to mercury was calculated based on how often people ate different types of fish, taking into account that sardines and salmon, for example, contain relatively low levels of the metal.
They also measured mercury levels found in toenail samples from people with MND and the healthy control group.
WHAT IS MND?
Motor neurone disease, also known as amyotrophic lateral sclerosis (ALS) is a rare condition that progressively damages parts of the nervous system.
it is also known as Lou Gehrig’s disease after the condition was named after the US baseball player when he was diagnosed in 1939 at just 36 years old.
It occurs when specialist nerve cells in the brain and spinal cord called motor neurones stop working properly – known as neurodegeneration.
Life expectancy for about half of those with the condition is three years from the start of symptoms.
However, some people may live for up to 10 years, and in rarer circumstances even longer.
The condition can affect adults of all ages, including teenagers, although this is extremely rare.
It’s usually diagnosed in people over 40, but most people with the condition first develop symptoms in their 60s. It affects slightly more men than women.
There’s currently no cure for motor neurone disease.
Treatment aims to make the person feel comfortable and have the best quality of life possible
It also tries to compensate for the progressive loss of bodily functions such as mobility, communication, swallowing and breathing.
Source: NHS Choices
Among participants who ate fish and seafood regularly, those in the top 25 per cent for estimated annual mercury intake were at double the risk for the condition compared to those with lower levels.
A total of 61 per cent of people with MND were in the top 25 percent of estimated mercury intake, compared to 44 per cent of people who did not have it.
Dr Elijah Stommel, lead author of the study which will be presented at a meeting of the American Academy of Neurology, said: ‘For most people, eating fish is part of a healthy diet. But questions remain about the possible impact of mercury in fish.’
Mercury is released into the environment mainly by coal-fired power stations, family homes which use coal for heating and cooking, industrial processes, waste incinerators and the mining industry. It builds up as methylmercury in fish and shellfish.
Fish and seafood consumption as a regular part of the diet was not linked with MND in the latest study. But shark and swordfish were among those with higher levels of mercury, which were more likely to put people in the top 25 per cent linked to the condition.
When Stephen Hawking was diagnosed with MND, at the age of 21, he was given only two years to live but recently celebrated his 75th birthday.
However there is no cure and around six people a day are diagnosed, eventually facing a future where they may be locked in a failing body, unable to move, talk and eventually breathe.
Dr Brian Dickie, director of research development at the Motor Neurone Disease Association, said: ‘Whilst these findings raise an intriguing theory that eating certain types of fish may be linked to a slightly higher incidence of ALS, the results would need to be independently verified.
‘Mercury may represent a risk factor for neurodegenerative conditions such as ALS but, if so, it is a very small risk and certainly not a primary cause of the disease.’