In humans, ergothioneine is acquired exclusively through the diet and accumulates in erythrocytes, bone marrow, liver, kidney, seminal fluid, and eyes.

So eating cum lowers your dementia risk too?

Foods found to contain ergothioneine include liver, kidney, black beans, kidney bean, and oat bran, with the highest levels in bolete and oyster mushrooms, especially in Pleurotus citrinopileatus.

“Eliminating benefit of vegetables” almost makes it sound as if it counteracts the positive effects of vegetables, which is not quite right—and I’m assuming not your intention, either, but the details are worth getting into. Here’s what the introductory results section says:

In subgroup analyses stratified by daily vegetable intake, higher serum ergothioneine levels were consistently associated with lower dementia risk, irrespective of vegetable consumption.

In other words, they’re just emphasizing that this effect of ergothioneine (“a dietary antioxidant abundantly found in many edible mushrooms, including oyster mushrooms, maitake mushrooms, and porcini mushrooms”) is still found even after controlling for vegetable intake. Bit more detail here:

Since vegetable intake may influence the association between serum ergothioneine levels and risk of dementia, we further examined the combined influence of serum ergothioneine levels and vegetable intake on the risk of developing all‐cause dementia (Fig. 3). Compared to the participants with low vegetable intake and a low serum ergothioneine level, the multivariable‐adjusted risks of dementia decreased significantly in those with a high serum ergothioneine level, irrespective of daily vegetable intake levels. In the subgroup analysis of daily vegetable intake levels, higher serum ergothioneine levels taken as a continuous variable were significantly associated with lower risk of dementia both in the subgroup with daily vegetable intake level of <165.0 and that with intake of ≥165.0 g/day (Table 3 [not reproduced in this comment]).

Hazard ratios of developing dementia according to serum ergothioneine levels and total vegetable intake. The risk estimates were adjusted for age, sex, education status, systolic blood pressure, antihypertensive medication, diabetes mellitus, serum total cholesterol, body mass index, electrocardiogram abnormalities, history of stroke, smoking habits, alcohol intake, regular exercise, and total daily vegetable intake.

In this graph, they split the cohort into two groups for each of two variables (with the split points being 0.693 µmol/L serum ergothioneine and 165 g/day vegetable intake), adjusted for (all?) other variables, then showed the hazard ratio relative to the low vegetable-intake and low serum ergothioneine group for each of the three remaining combinations. What you can see from this graph is that, for the people with low serum ergothioneine levels, increased vegetable intake shows a moderately protective but not statistically significant effect (HR=0.81 (0.52-1.25), which is the difference you see between the first bar from the left (low vegetable intake, low serum ergothioneine) and the second (high vegetable intake, low serum ergothioneine). But the third and fourth bars (low vegetable intake, high serum ergothioneine and high vegetable intake, high serum ergothioneine, respectively) are each significantly smaller than the first bar one and not significantly different from each other (low veg, high serum: HR=0.58 (0.39-0.87); high veg, high serum: HR=0.59 (0.37-0.93).

I assume it’s this last point which you described as “eliminating benefit of vegetables”, which does appear to be true for this specific measures of dementia in this study, but I don’t want the takeaway for anyone to be “I only need to eat mushrooms now!”. In the discussion section, they say

Finally, two prospective longitudinal studies reported that higher vegetable intake is associated with a reduced risk of dementia. ³¹ , ³² There was thus a chance that the significant negative associations between serum ergothioneine levels and dementia risk observed in the present study were merely a reflection of vegetable intake levels. However, even in our multivariable‐adjusted analysis that included daily vegetable intake and in our subgroup analysis of daily vegetable intake levels, a significant association was observed between higher serum ergothioneine levels and reduced risk of dementia. Collectively, the above findings support the results of this study, suggesting that mushroom and ergothioneine intake may be useful for reducing dementia risk.

The results of this study might indicate that ergothioneine is the predominant lurking variable in those other longitudinal intake studies, but it’s possible that vegetable intake has an independent effect as well—way above my pay grade to make any claims about that, especially since the authors don’t seem to make a strong claim like that.

Anyway, it sounds like I need to start chowing down on mushrooms! Thanks for sharing the paper.

(also if I screwed up with the statistics talk somewhere please let me know—stats has never been my strength.)

TL;DR: “even in our multivariable‐adjusted analysis that included daily vegetable intake and in our subgroup analysis of daily vegetable intake levels, a significant association was observed between higher serum ergothioneine levels and reduced risk of dementia.”

BE NOT AFRAID