“Kōji” Not the Culprit: Finding the Causes of the Kobayashi Pharmaceutical Supplement Scare

Major Health Scare, Misplaced Fears

Japan is today in the midst of a nutrition-related scare, with dozens hospitalized for kidney damage and multiple deaths reported in connection with dietary supplements produced by Kobayashi Pharmaceutical. This scare is spreading rapidly through society in part because of a lack of understanding of the main ingredient in the products in question, beni kōji, or red yeast rice.

As a researcher specializing in fermented foods, it concerns me greatly to see the commonly held misconceptions about kōji, the Aspergillus oryzae mold used in the production of everything from soy sauce and miso to sake and shōchū, and beni kōji, which—despite sharing the kōji character in its name with the former—is a different substance altogether, the product of strains of the Monascus yeast species grown on rice. It needs to be stated clearly that beni kōji is unlikely to be at fault in the ongoing crisis, and kōji is a broadly used substance that poses no threat whatsoever to health.

As far back as the Kamakura (1185–1333) and Muromachi (1333–1568) periods, Japan was home to a thriving industry making use of kōji in foodstuffs and beverages. High-quality kōji mold was cultivated by seed kōji growers known as moyashiya and sold to sake breweries and other businesses.

Beni kōji, meanwhile, was traditionally used on the Chinese mainland and in Taiwan to produce drinks like hongjiu and laojiu, “red liquor” and “aged liquor,” respectively. It is also an ingredient in the traditional Okinawan dish tōfu yō, a fermented tofu with a consistency like cheese. In the production of all these drinks and foods, beni kōji has a lengthy history and its safety as an ingredient has long been recognized.

Tōfu yō, a beni kōji dish often eaten with alcoholic drinks in Okinawa. (© Pixta)

The Need to Nail Down the Unknowns

The dietary supplements suspected of causing health damage to users contain beni kōji and promise to lower cholesterol. The particular products in question were made at a limited number of factories during a specific period of time, making it less likely that the harm is due to the basic ingredients in them. Kobayashi Pharmaceutical has announced the possibility that an unknown substance was introduced to them at some point during the manufacturing process. Needless to say, the media’s reporting on a dangerous “unknown substance” has prompted fear among many.

I must stress, though, that it is only natural for unidentified substances to be included in products made through fermentation. The world of microorganisms is one where we cannot be certain what reactions will take place, and to what extent, due to variations in the condition of those microorganisms and the environments where they grow. This is a field where we still have much to learn, and research in the area is constantly turning up new discoveries.

Of course, we never want to see the inclusion in food, drink, or supplements of unknown substances that pose a threat to health. To prevent this, humans have put centuries of experience and scientific knowledge to use in selecting the microorganisms that pose the least risk. Until the current scandal emerged, Kobayashi had also been controlling this risk appropriately, with strict management of its production processes.

When the first reports emerged of kidney damage, suspicion fell on a contaminant called citrinin. This is a form of mold that may be produced as a byproduct of beni kōji in some cases, and scientists have identified it as a threat to kidney health. The European Union has pointed to citrinin as a reason to heavily regulate beni kōji supplements; in some countries, all sales of products containing beni kōji are banned.

Kobayashi, though, produces all of its own beni kōji in house, and genomic analysis has confirmed that the seed strain it uses does not produce citrinin. Analysis of the content of the supplements used by people suffering kidney damage has also shown that citrinin is not present in them. This leaves the possibility that despite the company’s mechanisms to control its ingredients and production processes, another unexpected substance has been formed in or introduced to the products at some stage.

Until we can identify that substance, though, consumers will continue to be suspicious of these products. Over a week has now passed since the scandal came to light, and we are starting to hear theories about contaminants making their way into the supplements during production, or sudden mutations in the beni kōji yeast being used. We can only hope that the true cause will be pinpointed as soon as possible.

(Originally published in Japanese on March 29, 2024, based on an interview by Ōgitani Mika. Banner photo: the beni kōji used as a raw material for the supplements in question. Courtesy of Kobayashi Pharmaceutical; © Jiji.)