@gentlepotato basically, thiamine deficiency is almost as prevalent as hypothyroidism, in the two are very much intertwined.
It's an enzyme transporter, responsible for multiple parts of the ETC, and whole host of things. It's very easily depleted by oxphos, and by metabolizing alcohol.
Thiamine is actually very cheap if you buy powder and put it in capsules. I use benfotiamine. At first I took a couple grams a day, and it took a week before it started to excrete in the urine.
Incidentally, high dose thiamine cured my "seasonal allergies" where I would wake up every day congested or only able to breath through one nostril.
@takethiamine on X has detailed threads about B1maxxing.