Shark fins contain high levels of a potent neurotoxin that scientists have linked to neurodegenerative diseases like Alzheimer and Parkinson.
The study was the first to find the toxin, BMAA, or Beta-methylamino-L-alanine, in sharks, a researcher at the University of Miami.
BMAA is produced by virtually every known species of cyanobacteria, a ubiquitous algae-like microbe present in freshwater and saltwater worldwide.
The study suggests that the toxin can accumulate up the food chain, increasing in concentration as one animal eats another.
A growing body of research suggests there may be a connection between exposure to the toxin and the development of neurodegenerative diseases like Alzheimer’s, Parkinson’s and Lou Gehrig’s disease, also known as amyotrophic lateral sclerosis, or A.L.S.
More recent research has found high levels of BMAA in the brains of some people who died from Alzheimer’s and Parkinson’s, but not in the brains of other people with similar backgrounds and physiology who died from other conditions, said Douglas C. Lobner, a Marquette University researcher who was not involved in the study. These concentrations are similar to those seen in the Guam fruit bat — and now, in shark fins.
The toxin has been shown to incorporate itself into brain proteins in animal studies, causing protein tangles like those seen in neurodegenerative conditions, Dr. Mash said.
BMAA also acts synergistically with other neurotoxins like mercury; research has shown that when sublethal amounts of the two are combined, they become exponentially more deadly. That is of particular concern because shark fins are often contaminated with mercury and other heavy metals.
Report has found BMAA in other foods, including a type of Peruvian soup and a species of fish in Japan. In each case — as with the Guam bats and shark fin soup — people generally describe the taste as delicious and are willing to pay a lot to obtain it. This may be because the toxin binds to glutamate receptors, possibly like those found in “umami” taste buds, said Dr. Cox and his colleague, Sandra Banack.
Dr. Cox emphasized that this remains a hypothesis, however, as does the link between BMAA and neurodegenerative conditions. But that does not mean it is necessarily smart to dine on shark.