On call: Proscar and osteoporosis

I am 76 years old, and I?ve had an enlarged prostate for at least 10 years. I?ve been taking Proscar for about a year, and it seems to be helping quite a bit. I have not noticed any side effects, but I?m worried that if the medicine reduces testosterone levels enough to shrink my prostate, it will also give me osteoporosis. Should I change medications, or take Fosamax like my wife?