Long-term exposure to a toxin produced by blue-green algal blooms can trigger tangles in the brains of animals similar to those seen in the brains of humans with Alzheimer's disease and other neurological conditions, a study has found.

Key points: Blue-green algae is common in the environment

Blue-green algae is common in the environment Exposure to high doses of toxins increases brain tangles in animals

Exposure to high doses of toxins increases brain tangles in animals Brain tangles reduce in animals if diet supplemented with amino acid L-serine

"As far as we are aware, this is the first time researchers have been able to successfully produce brain tangles and amyloid deposits in an animal ... through exposure to an environmental toxin," said the study's lead author Dr Paul Alan Cox, an ethnobotanist at the Institute for EthnoMedicine.

The study, published in the journal Royal Society Proceedings B, also identified a common supplement decreased the number of brain tangles in animals exposed to the toxin.

Researchers have suspected a link between environmental triggers and Alzheimer's disease since the discovery of an unusual illness that included features of dementia, Parkinson's disease and motor neurone disease, which affected Chammoro villagers from the Pacific island of Guam in the 1960s.

The illness was thought to be caused by a toxin called BMAA, produced by cyanobacteria — commonly known as blue-green algae — in the roots of a cycad plant on the island. The villagers used the seeds from this tree to make flour.

To emulate the conditions experienced by the Chammoro villagers, Dr Cox and his colleagues fed high doses of toxin to a group of primates called vervets for 140 days, while others were fed regular food or a combination of the toxin and an equally high dose of an amino acid called L-serine.

While the vervets given regular food did not develop brain tangles, those given the toxin did. Animals fed both the toxin and the amino acid had reduced rate of brain tangles.

Blue-green algae common in the environment

Dr Rachael Dunlop, a visiting associate in the Faculty of Medicine and Health Sciences at Macquarie University, said the study showed strong evidence the toxin triggered brain tangles.

"We've been looking at the role of environmental toxins for a very long time," Dr Dunlop said.

She was not involved in the latest study, but is also studying the role of blue-green algae and disease for the Institute of EthnoMedicine.

Although blue-green algae does not always produce toxins, it is very common in the environment, she said.

"This would be very familiar to people as it appears as green scum on water bodies," Dr Dunlop explained.

She said it had also been found in seafood, particularly mussels, prawns and crabs that feed on the algae.

Cyanobacteria, known as blue-green algae, is very common in water. ( Supplied: CSIRO ScienceImage CC BY 3.0 )

"You don't just have to live on Guam and eat cycad trees to be exposed to this toxin," she said.

Although the toxin has been found in many countries such as France, South Africa, Britain and the US, there is little evidence of it in Australia.

"I have no reason to believe it's not here because we know it's everywhere," Dr Dunlop said.

However, she said most people would not be exposed to the high doses of the toxin used in the experiment.

"We haven't got any handle on how much people might be exposed to as they go about their daily life — it's probably very low," she said.

And not everyone exposed to the toxin would develop dementia, she added.

"There's going to be a whole bunch of factors that come together, because importantly ... if this toxin seems to be enriched in the environment, why don't we all have dementia?" she said.

Role of amino acid in prevention

Dr Dunlop said the focus of research now was to investigate whether or not the amino L-serine that reduced the development of brain tangles in the experiment could help slow down the early stage of Alzheimer's disease in humans.

But first, she said, scientists needed to work out if the supplement was safe.

"We cannot recommend that people start taking it," she cautioned.

"We are currently starting phase 1 trials in the US looking at the safety of this particular supplement in humans."

In the meantime, she said people could take simple steps to avoid exposure to the toxin.

"We're not suggesting people stop eating certain foods but ... if you're surfing or swimming or doing recreational activities in lakes that have green scum, it's probably not a good idea," Dr Dunlop said.