"Earthrise Nutritionals and Cyanotech Corp. are proactively responding to alleviate possible consumer concerns about spirulina consumption," said Kristen McCarthy Thomas, speaking for the companies. Cyanotech is a Hawai'i company that produces natural projects from microalgae. Earthrise, a California firm, produces and sells spirulina products.

Hawai'i researcher Paul Cox was among the scientists who published a paper earlier this month indicating that a toxin found in some cyanobacteria may be linked to a class of diseases that include Alzheimer's and Lou Gehrig's disease.

A neurotoxic amino acid was found in several different cyanobacteria or blue-green algae.

Earthrise and Cyanotech said the Cox group did not study the type of cyanobacteria that produces spirulina. The firms have asked the researchers to conduct tests on the product to determine whether the specific neurotoxin they cited is present.

"The dietary supplement has a recorded history of safe use ... We have not received any complaint concerning health problems related to neurological conditions. On the contrary, the antioxidant and anti-inflammatory effects of spirulina have been demonstrated in several animal studies," the firms said in a statement.