Re: Is it true that Apple cider vinegar may lower iodine levels over time?

I see no reason why ACV should lower Iodine levels, nor salt of course.
I had similar experience like you when I went vegetarian years ago; two first years was great, then a gradual decline of my health, after 4-5 years I had to realize I was hypo T.

The lack of Iodine whatever our diet is more likely the cause, plus the overload of competing halogens like bromide and fluoride.