I've heard that drinking coffee can reduce your height. I've been avoiding coffee since last year.
You're going to shrink if, for no other reason, than the disks between your vertebrae compress. If you're worried about Osteoporosis then start lifting weights and make certain you have enough calcium, vitamin D and other bone healthy nutrients.
I've never seen anything correlating caffeine and height except for children (which is disputed).
Don't forget to cut out tea, colas, and chocolate as well.