A combination of endogenous (genetic and hormonal) and exogenous (nutrition and physical activity) factors influence skeletal development during growth, bone maintenance during adulthood, and bone resorption during aging (Cadogan et al. 1997, Rizzoli et al. 2010). Figure 12.1 describes the factors that affect the development and loss of peak bone mass. Genetics account for 60%–80% of the peak bone mass variance (Rizzoli et al. 2010). Moreover, dietary calcium predicts 10%–15% of skeletal calcium retention during adolescence (Weaver 2008). Peak bone mass is usually achieved by age 30. Therefore, consuming the recommended doses of calcium and vitamin D in adolescence and young adulthood will ensure peak bone mass development (IOM 1997, Heaney et al. 2000).