The Z-Score compares your bone density to that of a person your own age. It is the number of standard deviations above or below the mean for your age. It is not used in making medical decisions but gives you an idea of how you stack up to your peers. Remember that bone is not like concrete. It's a dynamic living tissue.
Normal bone goes through a continual growth and destruction.
If the breakdown of bone is greater than the rebuilding, bone is lost. Osteopenia is the first stage of bone loss. Speak with your physician regarding your specific risk factors. Remember, osteoporosis is a progressive and silent disease. Normal bone density today shouldn't make you complacent.