Bats, Fish and Amyotrophic lateral sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is a type of motor neuron disease, a group of rare neurological diseases that mainly involve the nerve cells (neurons) responsible for controlling voluntary muscle movement. Voluntary muscles produce movements like chewing, walking, and talking.

The disease is progressive, meaning the symptoms get worse over time. Currently, there is no cure for ALS and no effective treatment to halt, or reverse the progression of the disease. 1

The book, Tuesday with Morrie, told the story of Mitch Albom’s reconnection with his college professor, Morrie Schwartz, as he declined with ALS. 2

Stephen Hawking, the astrophysicist, has a rare form of ALS.

The Chamorro people of Guam have been afflicted with a form of motor neuron disease known as ALS-PDC with similarities to ALS as well as Alzheimer’s disease and Parkinson’s disease. The prevalence rate was 30%. 3

The paper was co-authored by Oliver Sacks (1933-2015), the neurologist and medical doctor who has published hundreds of scientific articles and books for a general audience. He wrote about neurological disorders and the history of science and nature. His best known book is The Man Who Mistook His Wife for a Hat and Other Clinical Tales. 4

The cause was tracked down to a non-protein amino acid, β-N-methylamino-L-alanine (which is why it is referred to as BMAA).

BMAA is produced by a number of species of cyanobacteria (commonly called blue-green algae even though it is not an algae). Cyanobacteria and BMAA was in the water in Guam. However, that was not sufficient to cause ALS. The water was taken up by the palms and stored in the dates that were eaten, but that was not sufficient. The dates were eaten by the fruit bats which were eaten by the locals. Since BMAA accumulates in the food as it consumed at each step, which was sufficient to cause the disease.

BMAA is not the only possible neurotoxin produced by cyanobacteria. Microcystis aruginosaz is a species of cyanobacteria that produces microcystins which are potent liver toxins. The Oregon Health Division has a regulator limit of 1 part per billion. Their tests of a certain health product showed 83 of 85 samples contained microcystins with 63 (72%) over the regulatory limit. 5

Whilst eating fruit bats is not common elsewhere, eating fish is. The consumption of fish in the US has risen 30% between 1950-2015 , although the amount varies according to the demographics of the sample. 6

Outbreaks of ALS has been associated with outbreaks of cyanobacteria blooms in Florida, 7 southern France, 8 New Hampshire, 9 Arabia, 10 and Sweden. 11

Increased levels of BMAA has been found in Alzheimer’s patients in Canada and the US. 12

Mercury is a common pollutant in fish and mercury has been found to accentuate the affects of BMAA. 13

Even if you do not eat fish, you can still be affected as fish meal is frequently fed to farm animals.

Methyl mercury and organochlorides from fish are fed to farmed fish that accumulate the toxins, which are then eaten by people. Fish meal is also fed to farm animals that accumulate the toxins. However, these animal products contain saturated fats which have a greater capacity to store the organochlorides along with the methyl mercury. 14

Lead another neurotoxin that has increased significantly in the environment, mostly from tetraethyllead that was added to petrol.

Whilst there is debate whether BMAA or neurotoxins cause ALS, it would seem prudent, given that dozens of researchers have found associations with ALS and BMAA and other neurotoxins, to remove any possible antagonist from our diet.

Last updated on Saturday 3 December 2022 at 20:53 by administrators

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  1. National Institute of Neurological Disorders and Stroke (2018) Amyotrophic Lateral Sclerosis (ALS) Fact Sheet. [online]. Available from:
  2. Albom, M. (2003) Tuesdays with Morrie. Time Warner Paperbacks.
  3. Cox, P. A. & Sacks, O. W. (2002) Cycad neurotoxins, consumption of flying foxes, and ALS-PDC disease in Guam. Neurology. 58 (6), 956.
  4. Sacks, O. (1985) The Man Who Mistook His Wife for a Hat and Other Clinical Tales. Summit Books.
  5. Gilroy, D. J. et al. (2000) Assessing potential health risks from microcystin toxins in blue-green algae dietary supplements. Environmental health perspectives. 108 (5), 435.
  6. SDA ERS (2018) USDA ERS – Food Availability (Per Capita) Data System [online]. Available from: (Accessed 5 March 2018).
  7. Brand, L. E. et al. (2010) Cyanobacterial blooms and the occurrence of the neurotoxin, beta-N-methylamino-l-alanine (BMAA), in South Florida aquatic food webs. Harmful Algae. 9 (6), 620–635.
  8. Masseret, E. et al. (2013) Dietary BMAA Exposure in an Amyotrophic Lateral Sclerosis Cluster from Southern France Gilles J. Guillemin (ed.). PLoS ONE. 8 (12), e83406.
  9. Caller, T. A. et al. (2009) A cluster of amyotrophic lateral sclerosis in New Hampshire: A possible role for toxic cyanobacteria blooms. Amyotrophic Lateral Sclerosis. 10 (sup2), 101–108.
  10. Banack, S. A. et al. (2010) The Cyanobacteria Derived Toxin Beta-N-Methylamino-L-Alanine and Amyotrophic Lateral Sclerosis. Toxins. 2 (12), 2837–2850
  11. Jonasson, S. et al. (2010) Transfer of a cyanobacterial neurotoxin within a temperate aquatic ecosystem suggests pathways for human exposure. Proceedings of the National Academy of Sciences. 107 (20), 9252–9257.
  12. Jonasson, S. et al. (2010) Transfer of a cyanobacterial neurotoxin within a temperate aquatic ecosystem suggests pathways for human exposure. Proceedings of the National Academy of Sciences. 107 (20), 9252–9257.
  13. Rush, T. et al. (2012) Synergistic toxicity of the environmental neurotoxins methylmercury and β-N-methylamino-L-alanine. Neuroreport. 23 (4), 216–219.
  14. Dórea, J. G. (2009) Studies of fish consumption as source of methylmercury should consider fish-meal-fed farmed fish and other animal foods. Environmental research. 109 (1), 131–132.

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