Hormonal

Exercise-induced amenorrhea in female runners is associated with significant reductions in cortical and trabecular bone density and mineral content compared to eumenorrheic runners and normal controls.

If you are a female runner who has stopped menstruating for more than 6 months, your bone density may be decreasing despite your high activity levels. This is likely due to low estrogen. You should consult a physician to address the amenorrhea, as exercise alone may not protect your bones in this state.