Looks like caffeine leeches calcium from you and can contribute to kidney stones:
http://story.news.yahoo.com/news?tmpl=story&cid=571&e=12&u=/nm/20040903/hl_nm/caffeine_kidneystones_dc
http://story.news.yahoo.com/news?tmpl=story&cid=571&e=12&u=/nm/20040903/hl_nm/caffeine_kidneystones_dc