LITHIUM! ...But ya know what, it's harder than hell to find out exactly how much is in common foodstuffs! One website says, grain is a major source and beef is not, and the next site states it vice-versa. :-( I searched for hours for a chart listing generalized quantities, and there seem to be NONE. (And they'd have to be generalized, because soil and water samples vary significantly from place to place.)
It's truly impressive -- the lack of knowledge about what this stuff does in the body! In large doses, lithium can be very effective in mental disorders, but what it does in the "normal" brain and body is still a bit of a mystery. Certainly it's known that lithium can damage the thyroid, and there's a list of nasty overdose symptoms, but descriptions of mechanisms are sadly incomplete.
Nevertheless, i feel that this might be a very important substance when it comes to thyroid problems. One site i found revealed that THERE at least, they know what this stuff does -- "lithium increases intrathyroidal iodine content, inhibits the coupling of iodotyrosine residues to form iodothyronines (thyroxine [T4] and triiodothyronine [T3]), and inhibits release of T4 and T3." Hmmmm.... It's no wonder that lithium administration can cause either hypO- or hypERthyroidism.
Having properties similar to sodium and potassium, and other minerals too, there's a lot of evidence that lithium interferes with all kinds of processes pertaining to them. In another place, i was reading about how lithium interacts with various supplements, herbs and spices, exacerbating some and limiting others. This site simply has some good general info....
Well, obviously i need to spend a lot more time reading up on the stuff. My preliminary impression is that it isn't really NEEDED by the body, but can be put to use the way other "natural medicines" are. The danger looks like it comes from our not knowing nearly as much about it as we should. ...And i STILL suspect it of being one of the elements in food that a thyroid-challenged person should beware of!