A Japanese pharmaceutical company is investigating 80 deaths possibly linked to a yeast-containing supplement it sells in Japan, the country’s health ministry said Friday, in a shocking increase from an earlier revelation that is focusing attention on how supplements are regulated.

The company, Kobayashi Pharmaceutical, in March had reported five deaths potentially linked to its CholesteHelp rice and red-yeast pills. Japanese government health officials said the supplement, which claimed to help reduce cholesterol, contained puberulic acid, a highly toxic compound that is a product of mold.

In response to the sudden surge in reported deaths, Health Minister Keizo Takemi said it was “extremely regrettable” that Kobayashi Pharmaceutical had not updated the ministry sooner. The company, which is based in Osaka, had not provided new information on deaths potentially linked to CholesteHelp since March.

Since then, Kobayashi Pharmaceutical has received reports that 1,656 people sought medical advice for CholesteHelp-related health concerns, and 289 people have been hospitalized, the company reported. CholesteHelp has been recalled in Japan and China, the only countries the supplement was sold in, according to a spokeswoman for Kobayashi Pharmaceutical.

Mr. Takemi said the government would step in to take a more active role in investigating, after allowing the company to self-report its findings. “We cannot leave Kobayashi Pharmaceutical alone to handle it anymore,” he said.

Kobayashi Pharmaceutical was founded in 1919. While it is not one of Japan’s top pharmaceutical companies, it produces a variety of supplements and health products such as hand warmers and air fresheners, some of which are sold in the United States and elsewhere in Asia.

Quality-control guidelines related to supplements and other products making health claims were established in Japan in 2015. Those regulations are perceived to be less stringent than Japan’s rules governing prescription medications. Companies are typically responsible for self-reporting compliance rather than undergoing state screenings.

In the United States, where the dietary supplement market is booming, organizations like the American Medical Association have urged the Food and Drug Administration to introduce stricter rules to ensure supplement safety. Dietary supplements marketed for weight loss and muscle building have been linked with a number of deaths in the United States.

At a news conference in March when the potentially CholesteHelp-related deaths were first disclosed, the president of Kobayashi Pharmaceutical, Akihiro Kobayashi, apologized for not providing information sooner and said he had “no words.”