How does liver suppress thyroid function?

Ray Peat says it's not good to eat liver too often (more than 2 times a week, I think) because it suppresses thyroid function. What is it about liver that suppresses thyroid function?

 

It's the large amount of Vitamin A (retinol) that can suppress the thyroid.

"Since vitamin A is highly unsaturated, in excess it suppresses the thyroid, so it has to be balanced with the thyroid"

And

"I avoid carotene, because it blocks thyroid and steroid production, and very large, excessive, amounts of vitamin A, retinol, can do the same. I use halibut liver oil-derived vitamin A, or retinyl palmitate."

From Danny Roddy's: Ray Peat's Brain Post - (ctrl + f "vitamin A")

 

I had the impression that liver suppressed thyroid function for another reason. A serving of liver typically has 25,000 IU of vitamin A, and RP mentioned that he took 100,000 IU of vitamin A daily at some point.

 

Yes someone asked ray and ray said he thinks there are other things in liver that suppress thyroid besides vitamin A.