Majority of adolescents have far less than optimum vitamin D levels
Vitamin D in adolescents: Are current recommendations enough?
The Journal of Steroid Biochemistry and Molecular Biology, Volume 173, October 2017, Pages 265-272 https://doi.org/10.1016/j.jsbmb.2017.02.010
First presented at Vitamin D Workshop, March 2016
Taryn J.Smith, Susan A.Lanham-New, Kathryn H.Hart

Highlights
Adolescents are a population sub-group particularly vulnerable to low vitamin D status.
Current intake recommendations of 10–15 μg/day may help avoid vitamin D deficiency (25(OH)D < 25–30 nmol/l).
However higher intakes of 20–50 μg/day may be required to achieve adequacy (25(OH)D 50 nmol/l).
Dose-response studies are needed to determine optimal 25(OH)D concentration for maximal bone accretion in adolescents and the intake requirements to achieve this.
Vitamin D is essential for bone development during adolescence and low vitamin D status during this critical period of growth may impact bone mineralization, potentially reducing peak bone mass and consequently increasing the risk of osteoporosis in adulthood. Therefore, the high prevalence of vitamin D inadequacy and deficiency in adolescent populations is of great concern. However, there is currently a lack of consensus on the 25-hydroxyvitamin D [25(OH)D] concentration, the widely accepted biomarker of vitamin D status, that defines adequacy, and the vitamin D intake requirements to maintain various 25(OH)D thresholds are not well established. While the current intake recommendations of 10–15 μg/day may be sufficient to prevent vitamin D deficiency (25(OH)D < 25–30 nmol/l), greater intakes may be needed to achieve the higher threshold levels proposed to represent adequacy (25(OH)D > 50 nmol/l). This review will address these concerns and consider if the current dietary recommendations for vitamin D in adolescents are sufficient.