Soda DOES NOT have carbonic acid. It has carbon dioxide, and no, it won't soften the bones. Most of the CO2 is released when you burp anyways. One reason I can think of where caffeine can be bad for bone health is that caffeine is a diuretic. It makes you urinate alot. When you urinate, you lose minerals, mostly potassium and some sodium. Potassium and sodium, along with calcium, are largely responsible for bone density. That's the only thing I can think of. Anyone care to comment on that?