not following instructions

My HMO periodically sends out health newsletters. One of the common themes is "how to take care of your bones". I've heard the recommendations many times: take calcium with vitamin D, walk, run, and lift weights. Ironically, although one would think the calcium recommendation would be the easiest one to follow, it's the only one that I find difficult. I have three or four bottles of assorted vitamins in my desk at work, and they're all over four years old. (I wonder if vitamins go bad?)