Hi Phyllis:  According to the National Institute of Health several things can interfere with the absorption of calcium.  Here's a link to that site that explains the various items that can cause this.   If you don't get adequate vitamin D from the sun, then you'll need to supplement with oral D.  Some people with low vitamin D levels also have low calcium, so you may want to have this checked.   If you're not sure you want to try Fosamax here's a link from Dr Gonter that explains the other medications that are available to treat osteopenia/osteoporosis.   Some diuretics can cause problems with calcium absorption, read article.   Good luck...