Bones naturally become thinner as people grow older because, beginning in middle age, existing bone cells are reabsorbed by the body faster than new bone is made. As this occurs, the bones lose minerals, heaviness (mass), and structure, making them weaker and increasing their risk of breaking. All people begin losing bone mass after they reach peak bone mineral density (BMD) at about 30 years of age. The thicker your bones are at about age 30, the longer it takes to develop osteopenia or osteoporosis.
Some people who have osteopenia may not have bone loss; they may just naturally have a lower bone density. Osteopenia may also be the result of a wide variety of other conditions, disease processes, or treatments. Women are far more likely to develop osteopenia and osteoporosis than men. This is because women have a lower peak BMD and because the loss of bone mass speeds up as hormonal changes take place at the time of menopause. In both men and women, the following factors can all contribute to osteopenia: