THURSDAY, March 1 (HealthDay News) -- Shark fins contain high levels of a neurotoxin called BMAA, which is linked to neurodegenerative diseases in humans such as Alzheimer's and Lou Gehrig's disease (amyotrophic lateral sclerosis), according to a new study.

The findings suggest that people who eat shark fin soup and shark cartilage pills may be at significant risk for these diseases, the University of Miami researchers warned.

The scientists tested seven shark species -- blacknose, blacktip, bonnethead, bull, great hammerhead, lemon and nurse -- in waters throughout South Florida.

"The concentrations of BMAA in the samples are a cause for concern, not only in shark fin soup, but also in dietary supplements and other forms ingested by humans," study co-author Deborah Mash, director of the University of Miami Brain Endowment Bank, said in a university news release.

The new study was published Feb. 21 in the journal Marine Drugs.

In a study published in 2009, Mash and her colleagues found that patients dying of Alzheimer's disease and amyotrophic lateral sclerosis had unusually high levels of BMAA in their brains, up to 256 nanograms per milligram (ng/mg). In comparison, healthy people had only trace amounts or no BMAA in their brains.

The new study found BMAA levels of between 144 and 1,836 ng/mg in the shark fins.

Many shark species are on the road to extinction because of the demand for shark fin soup, the authors said. "Because sharks play important roles in maintaining balance in the oceans, not only is shark fin soup injurious to the marine environment, but our study suggests that it is likely harmful to the people who are consuming them," co-author Neil Hammerschlag, director of the university's marine conservation program, said in the news release.

More information

The U.S. National Library of Medicine has more about neurodegenerative diseases.