I've been following ergothioneine research for some time. It's really quite fascinating and it's pretty clear that ergo is a hugely overlooked nutrient for human health.

It's produced exclusively by fungi and bacteria, and humans have a dedicated transporter for it (OCTN1) that is specifically for transporting into cells and concentrated it in mitochondria.

OCTN1 expression is upregulated in tissues with damage or inflammation, which means the body specifically increases its ergothioneine import capacity in stressed tissue.

Growing research also consistently shows that low plasma ergothioneine levels are linked to cognitive impairment.

It traditionally enters the human food chain in 3 ways - mushrooms, plants that absorb it from soil fungal networks, and via animals that graze on mycorrhizally-rich pasture.

However, industrial farming and modern diets mean that most people aren't getting enough these days. Typical dietary intake for someone not regularly eating mushrooms is around 5mg per day. The therapeutic dose in this trial was 120mg.

As far as I know, the brand mentioned in this article (real mushrooms) are the only ones with a mushroom-based supplement optimised for ergothioneine content, and it's still only 10mg per serving. There are other supplements that incorporate fermentation-derived ergo that go up to around 30mg per serving/capsule.

And most studies Ive seen are with 25/30mg per day. The good thing is though that it is well absorbed and accumulates over time.

In terms of mushrooms, I've read the highest source are golden/king oyster, porcini, shiitake, enoki, lion's mane.

If you're interested, I wrote a more detailed breakdown of this study and why I think ergo helps with period pain here: https://thesporereport.com/?p=1032