A 49-year-old man reached end-stage renal disease after years of daily chaga powder. When his nephrologists measured the oxalate content of what was left in his jar, it came back at 14.2 grams per 100 grams. At that concentration a single level teaspoon delivers more oxalate than most people get from an entire day of food — and chaga is the one mushroom this applies to.
Culinary and medicinal mushrooms are, as a group, not a significant oxalate source. Chaga is the exception and it is an extreme one: measured at 14.2 g per 100 g in a Korean case investigation, roughly 142 mg of oxalate per gram of powder, against a typical Western dietary intake of 100–200 mg per day. Two published cases document the consequence. In the first, long-term chaga powder use produced chronic tubulointerstitial nephritis with oxalate crystal deposits and end-stage renal disease, with estimated oxalate intake two times usual for four years and five times usual for one. In the second, 10–15 g a day of chaga powder alongside 500 mg of vitamin C for three months produced acute kidney injury presenting as nephrotic syndrome, with calcium oxalate crystals in the tubules. Oxalate is water-soluble, so brewing it into tea transfers it rather than removing it.
This is a narrow, specific, well-documented risk attached to one product, and it gets lost inside general reassurance that mushrooms are good for you. Most of them are. This one needs a dose ceiling.
What Oxalate Does to Kidneys
Oxalate binds calcium and forms crystals. In urine those crystals are the basis of the commonest kidney stones; deposited in kidney tissue they cause oxalate nephropathy, an inflammatory and scarring injury to the tubules.
Most dietary oxalate never reaches the kidney, because gut bacteria degrade a portion of it and calcium in the same meal binds more into an unabsorbable form. The system copes well with ordinary food.
It copes less well with a concentrated daily load that arrives outside a meal, which is exactly how supplement powders are usually taken.
The Number That Makes Chaga Different
Lee's 2020 case report is the source of the figure. A 49-year-old Korean man presented with end-stage renal disease; kidney biopsy showed chronic tubulointerstitial nephritis with oxalate crystal deposits, and his history revealed long-term chaga mushroom powder taken for intractable atopic dermatitis.
The investigators measured what remained of his supply: 14.2 g of oxalate per 100 g. They estimated his daily oxalate intake as roughly twice usual dietary intake for four years, rising to five times usual for one year.
Convert that into a kitchen measure. At 142 mg of oxalate per gram, a 5 g teaspoon of chaga powder carries around 710 mg — several times a normal day's total dietary oxalate, in one spoon, in one go.
For context, the foods usually named in oxalate advice are spinach at roughly 600–750 mg per 100 g and rhubarb somewhat higher. Chaga powder measured an order of magnitude above those per unit weight.
The Vitamin C Stack Nobody Warns About
Kwon's 2022 case adds the mechanism that turns a marginal intake into an injurious one. A 69-year-old man took chaga mushroom powder at 10–15 g per day together with 500 mg of vitamin C daily for three months.
He developed acute kidney injury presenting as nephrotic syndrome. Pathology showed focal acute tubular injury with calcium oxalate crystal deposition in the tubules, interstitial fibrosis and tubular atrophy, plus podocyte foot-process effacement consistent with minimal change disease alongside the oxalate nephropathy.
The relevant biochemistry is that ascorbic acid is metabolised endogenously to oxalate. High-dose vitamin C therefore adds to the same pool the chaga is loading, and the two are commonly taken together by exactly the same wellness-minded person.
No chaga product carries that warning. It is a supplement-plus-supplement interaction with no drug in it, which is precisely the kind that falls through every gap.
Why Tea Does Not Solve It
Oxalate is water-soluble. That is why it is absorbed from food and why it appears in urine, and it is why simmering chaga chunks moves the oxalate into the tea rather than leaving it behind in the chunk.
So the traditional preparation is not the safer preparation from an oxalate standpoint. A long decoction is an efficient oxalate extraction. Our format comparison treats this as a safety choice rather than a taste one, and it is.
The only variable that reliably reduces exposure is how much chaga you consume per day and how many days you do it.
Is This a Mushroom Problem or a Chaga Problem?
A chaga problem. There is no comparable oxalate literature for reishi, lion's mane, cordyceps, Trametes Versicolor, shiitake, maitake or any culinary species. Organic acid profiling of wild edible mushrooms finds oxalic acid among the acids present, at concentrations nowhere near chaga's.
| Product | Oxalate concern | Evidence |
|---|---|---|
| Chaga powder | High — 14.2 g/100 g measured | Two case reports; ESRD and AKI |
| Chaga tea from chunks | High — oxalate is water-soluble | Mechanistic; same load transferred |
| Reishi, lion's mane, cordyceps | None documented | No case literature, no high measurements |
| Shiitake, maitake, culinary species | None documented | Ordinary food-level organic acids |
| Sea moss, spirulina | Not an oxalate question | Different risk profiles entirely |
| Chaga + high-dose vitamin C | Additive | Ascorbate metabolises to oxalate; documented case |
The practical effect of blanket "mushrooms and kidneys" advice is that it over-warns about the category while under-warning about the single product that earned the warning.
Who Should Avoid Chaga Entirely
Anyone with chronic kidney disease of any stage, anyone with a history of calcium oxalate kidney stones, anyone with reduced kidney function from any cause, and anyone with a condition causing fat malabsorption — inflammatory bowel disease, coeliac disease, bariatric surgery — because that state increases oxalate absorption substantially.
People on high-dose vitamin C should treat the combination as the documented risk it is. And anyone taking chaga daily for years, even with normal kidney function, is in the exposure pattern both case reports describe.
Our chaga side effects article covers the wider picture; this is the part that has put people on dialysis.
What Normal Use Looks Like
- Treat chaga as an occasional preparation, not a daily habit. Both documented cases involved sustained daily intake over months to years.
- Do not take grams of powder daily. The acute case used 10–15 g a day; the chronic case reached five times normal dietary oxalate.
- Do not combine chaga with high-dose vitamin C. Ascorbate becomes oxalate, and that exact combination is in the published acute case.
- Drink water generously on days you take it. Dilute urine is the main defence against crystal formation.
- Take it with a calcium-containing food. Calcium binds oxalate in the gut, reducing absorption — the same reason dairy is advised with high-oxalate foods.
- If you have any kidney history, choose something else. The benefit case for chaga is weak enough that this is not a difficult trade — see our reishi versus chaga comparison.
- Know the symptoms: reduced urine output, swelling, flank pain, unexplained fatigue. Oxalate nephropathy is quiet until it is not.
The Honest Summary
Two case reports are not an epidemiology, and millions of people drink chaga tea without consequence. What the two cases supply is the mechanism, the measurement and the dose pattern, and they agree with each other: a genuinely extreme oxalate concentration, taken daily, over a long period, in one instance with a co-supplement that adds to the same load.
That is enough to set a rule without panic. Chaga is not a daily-forever supplement, it is the wrong product for anyone with kidney history, and it should not be stacked with high-dose vitamin C. Every other mushroom on the shelf is outside this conversation, and it is worth being precise about that rather than spreading the warning across products it does not apply to.
Frequently Asked Questions
How much oxalate is in chaga?
In the one published measurement, 14.2 g per 100 g — about 142 mg per gram of powder. A 5 g teaspoon therefore carries roughly 710 mg, against a typical total dietary intake of 100–200 mg a day.
Can chaga cause kidney damage?
Two published cases document it. One describes end-stage renal disease with oxalate crystal deposits after years of daily chaga powder; the other describes acute kidney injury with calcium oxalate crystals after three months at 10–15 g a day alongside vitamin C.
Does making chaga into tea remove the oxalate?
No. Oxalate is water-soluble, so simmering transfers it into the liquid rather than leaving it in the chunk. Reducing the amount and frequency is the only thing that reduces exposure.
Do other mushrooms carry the same risk?
No. There is no comparable oxalate measurement or case literature for reishi, lion's mane, cordyceps, Trametes Versicolor or any culinary species. This is specific to chaga.
Is it safe to take chaga with vitamin C?
It is the combination in the documented acute case, and the reason is biochemical: ascorbic acid is metabolised to oxalate in the body, adding to the load chaga is already delivering. Avoid taking them together.
Shop Sensibly
If you enjoy chaga, buy it as an occasional drink rather than a daily powder: Chaga chunks (100 g €25, 300 g €39, 1 kg €59) are easy to use at low frequency and hard to over-consume by accident. If you want a daily mushroom and kidney history rules chaga out, Reishi capsules (120 caps €39) or Lion's mane capsules (120 caps €49) carry no oxalate concern. Free shipping on orders over €50.
Related Articles
- Chaga Side Effects and Interactions
- Chaga Mushroom Dosage Guide
- Chaga Powder vs Chunks vs Extract
- Reishi vs Chaga
- Chaga Tea vs Tincture vs Dual Extract
- Mushroom Supplements and Medication Interactions
- Heavy Metals in Mushroom Supplements
Sources
- Lee S, Lee HY, Park Y, et al. Development of end stage renal disease after long-term ingestion of chaga mushroom: case report and review of literature. J Korean Med Sci. 2020;35(19):e122. PubMed 32419395
- Kwon O, Kim Y, Paek JH, et al. Chaga mushroom-induced oxalate nephropathy that clinically manifested as nephrotic syndrome: a case report. Medicine (Baltimore). 2022;101(10):e28997. PubMed 35451393
- Magdziak Z, Gasecka M, Golinski P, Mleczek M. Characteristics of organic acid profiles in 16 species of wild growing edible mushrooms. J Environ Sci Health B. 2017;52(10):784-789. PubMed 28862514
- Garland V, Herlitz L, Regunathan-Shenk R. Diet-induced oxalate nephropathy from excessive nut and seed consumption. BMJ Case Rep. 2020;13(11):e237212. PubMed 33257378
- Whittamore JM, Hatch M. Oxalate flux across the intestine: contributions from membrane transporters. Compr Physiol. 2021;12(1):2835-2875. PubMed 34964122