Japan's health ministry says the maker of the "Beni-koji" fermented rice health supplement has confirmed the presence of "puberulic acid", an unintended substance, in its products. The products made by Kobayashi Pharmaceutical are reportedly linked to five deaths and dozens of hospitalizations. But the ministry says it is not certain whether the substance is the cause.

The company disclosed the finding at a panel of experts meeting held by the health ministry on Thursday.

The firm said the "puberulic acid", which can be produced from blue mold, was confirmed present in a batch of the products that caused health complaints.

More than 100 people who took the supplement have been hospitalized, and nearly 700 others are consulting doctors, or plan to do so.

The company earlier admitted that the batches of Benikoji CholesteHelp, manufactured between last April through December, could contain an "unintended substance."

Ministry officials say the acid is reported to have antimalarial properties. But they say it is not known how much of its consumption could harm people's health, or how it damages kidneys. They also say it is unknown how the unintended substance was mixed into the product.

The ministry will have the National Institute of Health Sciences analyze samples from the past three years to examine toxicity levels, while looking into the possibility that other substances may be contained in them.