Kikuchi Y., Seta K., Ogawa Y. et al. Chaga mushroom-induced oxalate nephropathy. Clin Nephrol. 2014;81(6):440–444. Ahn H.J. et al. Development of End Stage Renal Disease after Long-Term Ingestion of Chaga Mushroom. 2020 (PMC7234858). Park S. et al. Chaga mushroom-induced oxalate nephropathy manifesting as nephrotic syndrome. 2022 (PMC8913114).
Rationale
Chaga is one of the best-selling "medicinal" mushrooms — and it has a quality rare for the field: a measurable mechanism of harm. Dried chaga contains extreme amounts of oxalates — 14.2 g per 100 g of powder measured in the Korean case. Oxalates crystallize in renal tubules — a mechanism known from oxalic-acid poisoning and enteric hyperoxaluria. The question was whether this actually happens in people.
Documented cases
- Japan, 2014 (Kikuchi et al., Clin Nephrol): a 72-year-old woman drank chaga powder 4–5 teaspoons daily for six months "for treatment" after liver resection for cancer. Renal function fell to hemodialysis; biopsy — diffuse tubular atrophy and interstitial fibrosis with oxalate crystals in tubule lumens. The first described case.
- Korea, 2020 (PMC7234858): a 49-year-old man with end-stage renal disease; he had taken chaga for atopic dermatitis for years. Biopsy — chronic tubulointerstitial nephritis with oxalate deposits; estimated daily oxalate load exceeded the ordinary dietary load 2× over 4 years and 5× in the final year.
- Korea, 2022 (PMC8913114): a 69-year-old man, 10–15 g chaga powder + 500 mg vitamin C daily for 3 months → acute renal failure with nephrotic syndrome; after steroids and hemodialysis, function recovered within a month.
What it means
The mechanism is perfectly honest: chaga = a great deal of oxalate in concentrated form + prolonged daily intake + (in two cases) concurrent vitamin C, which metabolizes to oxalate. Not "chaga is dangerous to everyone," but "grams of chaga powder every day is a poisoning-level oxalate load."
Worth noting
Strengths of the data: biopsy confirmation (crystals in tubules — not a guess); measured oxalate content of the powder; three independent cases from two countries with outcomes from reversible injury to ESRD.
Limitations:
- Case reports — not an RCT; causality in individual cases is strong (biopsy + history + chemical analysis), but frequency is unknown.
- High and prolonged doses — cannot be extrapolated to chaga tea or short courses.
- Individual factors (cancer, dermatitis, vitamin C) modified the outcome.
- Practical lesson for the reader: chaga powder is not a harmless "tea" supplement; with kidney disease, urolithiasis and high-dose vitamin C it is a direct risk.