Mine were definitely caused by calcium building up over time from vitamin D supplements. I also was deficient in Vitamin A, Vitamin K and magnesium, which will do it to you. Sometimes I was getting too much exercise and too little water (due to rationing issues) while deployed a few times, that couldn't have helped me either. I passed a total of five over five months and I'm pretty sure I have scarring in my inferior kidney as a result. My kidney function test just came back normal three weeks ago.