Bone mineral density (BMD) is a key determinant of future fracture risk and occurs across a continuum from normal BMD to low BMD and osteoporosis. Genetic factors account for 60-80% of peak BMD. Dietary intake (e.g. energy, protein, calcium, vitamin D), hormonal status and weight-bearing exercise contribute to the remaining 20-40%. In women, 99% of peak BMD is attained by age 22.1±2.5yrs. The opportunity to further increase BMD is very limited after this time. Adolescence and the teenage years are, therefore, the most important time for accruing BMD to optimise peak BMD. Deficits in BMD during the pre-menopausal period result from either failure to attain peak BMD and/or as a result of bone loss. Thus, coaches and parents need to ensure young female athletes and exercising women are not experiencing an (inadvertent or intentional) energy deficit, primary or secondary amenorrhea and that they are conducting sufficient weight-bearing exercise. Ignorance is negligence.
Delayed menarche interferes with optimising peak BMD because there is less time available for the bone promoting benefits of estrogen to maximise BMD. That is, girls with delayed menarche enter adult life with lower BMD compared to women who begin menstruation at an earlier age. Further, despite regular loading, a large body of evidence has demonstrated that female athletes and exercising women with menstrual disturbances have lower BMD compared to their regularly cyclic counterparts. This suggests that the positive effect of exercise on bone is diminished when a woman has a menstrual disturbance.
Low energy availability also has a direct negative effect on BMD via effects on various metabolic hormones and substrates (e.g. cortisol, leptin). But, the combination of energy deficiency and low estrogen levels, characteristic of energy-related menstrual disturbances, has a more pronounced negative impact on BMD. It is important to note that BMD may not be fully restored when energy and estrogen status are once again optimised. Thus, low energy availability, with our without low levels of estrogen, poses a significant threat to the long term health of female athletes and exercising women by increasing the risk for fractures and premature osteoporosis.