A research team at Osaka University found that 87% of patients who suffered kidney function impairments after using Kobayashi Pharmaceutical’s beni kōji red yeast rice supplement continued to experience reduced kidney function, even after stopping their intake.
The findings, released Tuesday, were based on a survey of 192 patients reported by physicians affiliated with the Japanese Society of Nephrology. Researchers stressed the importance of long-term follow-up for affected patients.
The study, led by Yoshitaka Isaka, a professor at Osaka University’s graduate school of internal medicine, analyzed data from patients who reported health issues between late March and late April 2024. The research team tracked the progress of 114 of these patients until early June of the same year.
While many patients showed improvement in Fanconi syndrome — a condition where kidney tubules fail to reabsorb essential nutrients such as potassium and phosphorus — 87% still had kidney function indicators below standard levels. This was despite two months having passed since the company urged consumers to stop taking the supplement.
The team suggested the possibility of nephron reduction, the structures in kidneys responsible for filtering waste in the blood and producing urine.
Among 102 patients who underwent kidney biopsies, 50% exhibited tubulointerstitial nephritis (inflammation), while 32% showed evidence of tubular necrosis. The use of immunosuppressive steroid drugs, typically effective in kidney disease treatment, showed no benefits, leading researchers to propose that the kidney damage may stem from mechanisms unrelated to immune abnormalities.
“There were many patients whose kidney function remained impaired,” Isaka stated. “Further investigation will be necessary going forward.”
Translated by The Japan Times