I didn't try my regimen for a few days but for sometimes years for some.
I can't try some for years or months if a few days are too dangerous?
That doesn't make any sense. I think you need to reread what I wrote.

B12 I tried for a year and a half. I believe that should be long enough to see
if there was any positive effect. I can barely afford to take the local city bus, so all this experimentation was at the limits of my budgets.

I can't seem to edit my post so I will add this;
I take liquid tincture sea kelp as my iodine source. I'm aware of several types
of Iodine and many are NOT ingestible but only topical outside application. So
be careful of what type you try.

I said Iodine improved my hearing and vision. Well more accurately, it improved my awareness of sounds and improved my awareness of my visual field. So I don't think my actual ears and eyes improved.