Most of us eat fish on a regular basis, whether it is a delicious piece of hake or a tuna sandwich, but few of us is aware of the dangers of mercury in seafood.
Eating mercury-laden seafood may raise the risk of developing ALS (amyotrophic lateral sclerosis), preliminary research suggests.
According to the Council for Scientific and Industrial Research (CSIR), fish sold in South Africa’s retail stores contains mercury levels well above the World Health Organisation (WHO) guidelines.
Dr Brent Newman, a principal researcher at the CSIR, previously told Health24, “The risk depends on how much fish one eats.”
"For most people, eating fish is part of a healthy diet," said study author Dr Elijah Stommel, who's with Dartmouth College's Geisel School of Medicine in Hanover, New Hampshire.
"But questions remain about the possible impact of mercury in fish," Stommel said in an American Academy of Neurology news release.
The report warns of possible harm from fish containing the most mercury, such as swordfish and shark. It doesn't suggest a higher risk of ALS from general consumption of seafood.
The study of 500-plus people found that seafood eaters who ate the most mercury-heavy fish may face double the risk of developing ALS.
However, the study only established a link between the two, not a cause-and-effect relationship.
Mercury is a toxic metal that occurs naturally in the environment. It tends to be lower in fish such as salmon and sardines, and the study authors stressed that seafood confers many health benefits. But they suggested paying attention to what type of seafood you eat.
What is ALS?
ALS, an incurable neurodegenerative disease, is also called Lou Gehrig's disease in memory of the legendary baseball player who died from it. It often starts with muscle weakness or twitching and eventually develops into complete paralysis and death.
In the United States, just over 6,000 people are diagnosed with ALS each year, according to the ALS Association.
What causes ALS is unknown, but some research has identified mercury as a risk factor. Americans most commonly encounter mercury when they eat fish that contains it, the researchers pointed out.
For the study, the researchers surveyed 294 people with ALS and 224 without it.
Participants were asked about their seafood consumption and whether they caught it themselves or bought it. The researchers then estimated how much mercury the participants consumed annually. They also tested participants' toenail clippings for mercury content.
Mercury doubles risk of ALS
The results: 61% of those with ALS were in the top quarter of mercury consumption, compared to 44% of those without ALS.
Among regular seafood eaters, people in the top quarter of mercury consumption were at twice the risk of ALS, the researchers determined. People with the highest mercury levels, based on toenail clippings and diet, also had twice the risk, they said.
Dr Newman from the CSIR however cautions that people should not be afraid to eat fish. “Fish is very, very important in the human diet. What people should be doing is eating certain fish in moderation, based on the fish’s mercury content.
“This applies especially to pregnant women, those that want to become pregnant and nursing mothers. This is because mercury is a potent neurotoxin, and the neurological systems of children and infants are especially susceptible to the toxic effects of mercury.”