Eventually my friend learned that pagophagia is caused by iron deficiency. When she started eating more iron, her ice craving went away.
Why do we work this way? The evolutionary reason, I think, is that in the ancient world where this tendency evolved, a desire to crunch something was usually satisfied by crunching bones. After you discovered how pleasant it was to crunch bones, you sought them out.
Bone marrow is high in iron. Crunching those sought-out bones increased your iron intake.
The umami hypothesis says that we like umami tastes, sour tastes and complex flavors so that we will consume more harmless-bacteria-laden food (which keeps our immune system on its toes). In the ancient environment where these tendencies evolved, in other words, a desire to eat food with these characteristics led us to eat bacteria-laden food. At the Fancy Food Show, I met a maker of sparkling tea who was unable to get enough complexity without using bacteria.
Just as a person with pagophagia chews ice, most of us do one or more of these:
- add monosodium glutamate (e.g., Accent) for umami taste
- add vinegar for sourness (I put a few drops of vinegar in coffee-like drinks)
- add many spices for complexity
The result, I suspect, is that most of us have immune systems with plenty of room for improvement. I stopped getting easy-to-notice colds when I started sleeping better so the high frequency of reported colds (the average American adult gets about three per year) may be a sign that this is true.