Neurotoxin of Blue-Green Algal Blooms May Raise Risk of ALS

Exposure to a neurotoxic molecule produced by blue-green algae seems to raise a person’s odds of developing amyotrophic lateral sclerosis (ALS), particularly for those under 65, a population-based study from Italy shows.

The research examined individuals who lived close to freshwater systems — a river, lake, even a small pond — as a proxy for cyanotoxin exposure. While it suggests an association between toxins produced by these algae and ALS risk, larger studies are needed as the link did not reach statistical significance.

The study, “Living near waterbodies as a proxy of cyanobacteria exposure and risk of amyotrophic lateral sclerosis: a population based case-control study,” was published in Environmental Research.

A large number of environmental factors are thought to increase the risk of ALS, including the use of herbicides, exposure to environmental pollution and to heavy metals, and working with silica.

Studies also support a link between exposure to the cyanotoxins — neurotoxic molecules produced by cyanobacteria — and higher-than-usual ALS incidence in a number of populations.

To investigate further, researchers conducted a population-based study targeting three provinces of northern Italy – Parma, Reggio Emilia, and Modena – and the province of Catania in southern Italy.

Their study included 703 ALS patients and 2,737 others serving as controls, matched to patients by sex, age, and province of residence. All were examined for their place of residence to determine whether they lived close (within 100 meters, about 328 feet) from water bodies, where cyanobacteria are often found when  water is warm, stagnant, and rich in nutrients (often due to fertilizer runoff or septic tank overflows).

Researchers did not take water samples to evaluate for contamination. Rather, they assumed that those living closer to water bodies had been exposed to cyanotoxins, as these often end up in edible plants and in smaller animals.

In total, 12 patients (1.71%) and 33 controls (1.21%) were found to have been exposed to cyanotoxins, with those without ALS being slightly older than exposed patients.

A statistical analysis demonstrated that living near water bodies at the time of the analysis was associated with roughly 40% greater odds of having ALS, with these odds being higher in men, in people younger than 65, and in people living in the Modena province.

Living in the Reggio Emilia appeared to be protective for ALS, with individuals being 24% less likely to develop the condition.

Associations were replicated in three statistical models that adjusted the results for sex and province (model 1), age, sex, and province (model 2), and for age, sex, province, and total agricultural land use (model 3).  None of the associations reached statistical significance in any of the three models.

Researchers also found similar results for historical exposure: people who lived in the vicinity of water bodies in the previous 30 years had 30% greater odds of having ALS, and the association was stronger here in women. Again, no association reached statistical significance in any of the three models.

These findings suggest that living near water bodies may increase the risk of ALS, likely due to an increased exposure to cyanotoxins. This is in line with prior studies showing that subjects living near lakes with algal blooms had a higher ALS risk.

“Overall, using an index of environmental exposure to cyanotoxins based on proximity of residence to waterbodies in two areas of Northern and Southern Italy, we found some evidence of an association with excess ALS risk,” the researchers wrote.

“However, the interpretation of our findings is limited by the limited statistical precision of the risk estimates and some concerns about exposure assessment, thus highlighting the need for further studies on this issue,” they concluded.