Adolescence and acquisition of peak bone mass

The rapid bone growth accompanying puberty is vastly different than the adult state, that is, ∼90% of adult bone mineral content (BMC) is accrued by the end of adolescence, and ∼40% of adult BMC is accumulated during the 4 years surrounding peak BMC velocity. The Institute of Medicine (IOM) identified a serum 25(OH)D threshold of >50 nmol/L as being associated with optimal bone health in the United States and Canadian children, while Canada uses a threshold of 75 nmol/L. The IOM vitamin D requirement of 600 IU/d that is needed to achieve the 50 nmol/L cutoff for optimal bone health is not being met by most US children. In fact, a considerable number of children worldwide have serum values below this threshold, and adolescent bone strength gains could therefore be attenuated leading to an increased risk of skeletal fractures. Of the vitamin D randomized controlled trials conducted to date, there is moderate support for the role of vitamin D supplementation on BMC accrual in adolescents, particularly among those with baseline serum concentrations <50 nmol/L. Important factors, such as participant age, maturational stage, race, latitude, lifestyle factors, and vitamin D dose, were not consistent across studies. Further, data on males and population ancestries other than White were limited in these studies and reduced the generalizability of the findings. Finally, the recent interest linking vitamin D to muscle function, insulin sensitivity, and obesity needs to be explored further in randomized trials documenting not only the potential benefits, but also issues of safety.