**3. Osteoporosis associated BMD alteration**

Every human being is susceptible to develop osteoporosis especially by living long. The maximum humans' BMD is reached by 20 years of age; then, it starts decreasing naturally and gradually by approximatively 1%/year. The rate of this decrease variates depending on gender and can be accelerated by the use of steroid, lack of calcium and vitamin D, smoking, high alcohol consumption, and cancer treatments [15].
