I have a rather wild story to share on this topic. At one time I drank rather large quantities of Coca-cola daily. As some of you remember (and many, perhaps, never knew), I am a musician by training and first love. The first decade of my professional life was spent teaching music in the public schools. I was also, at some point, "gifted" with the gift of so-called "perfect pitch" ... that is, you play a note on most any instrument, I can tell you the name of the note (A, B, whatnot), and, generally, can identify song keys and chord types/changes simply by listening. Many musicians are trained to "hear" chord changes, but not so many can tell exactly what chords they are hearing without an outside reference.
Anyway, one morning about 12-13 years ago I walked into the band room for rehearsal and started the warm-up scales. After the first few notes, I was looking desperately at the trombonists' slides, because nothing sounded "right" at all. I couldn't tell one note from another, and it was scary. I couldn't really help the band rehearse, because I couldn't tell what the h*&^ they were playing. After class, I asked 3 of the girls who I knew sang well to come to the office ... they were working on a "contest piece" that they sang a capella, and the day before they had sounded really quite good. That morning, again, they sounded so off-key and just plain awful (or do I mean offal 😃 ). I suffered through the rest of the day.
Needless to say, I was rather concerned. After school I went to a doctor, an "ear/nose/throat" guy. He gave me a basic hearing test, (came up normal), and then basically said: "Well, this pitch sense thing is just a phenomenon, anyway. People have to have very sensitive hearing for that, and, as you age, you lose some hearing sensitivity. Welcome to the ranks of the 'normal people'...."
I wasn't too pleased with his answer. To shorten the story, next afternoon I went to the audiology center at a local hospital. They put me through an extensive test series in a sound-proof room, and then started asking me a jillion questions:
... [some question] (answer)
... [some question] (answer)
... [some question] (answer)
... are you diabetic? (no)
... do you have syphillis? (Heck, no!)
... do you drink a lot of coffee? (No.)
... (Wait a minute ... why did they ask me that one?)
As it turned out (you may have guessed) caffeine is a potent diuretic ... that is, it can dehydrate you, or parts of you. As best we could infer, because of my significant intake of caffeine [via Coke(r)], the cochlea (part of my inner ear) had become misshapen and the nerve endings inside it were not in the usual locations, causing my "internal wavelength measuring device" to hear frequencies differently than usual and making sound "out of tune".
I switched to Sprite immediately; it took some weeks and a bit of retraining to get my musical ear back "in tune", and I'm still not convinced I'm quite as accurate with it as I was prior to that experience. Now that I'm in my forties, even Sprite has gone the way of the do-do. H2O, baby, all the way 😉
). I suffered through the rest of the day.