The Association of Vitamin D in Youth and Early Adulthood with Bone Mineral Density and Microarchitecture in Early Adulthood.

This study aimed to describe the association of vitamin D status at different stages of growth with bone measures in adolescence and early adulthood. There were 415 participants followed from age 8 to 16, and 201 further followed to age 25. Areal bone mineral density (BMD) at the spine, hip and total body was measured by dual-energy X-ray absorptiometry at ages 16 and 25, and tibial and radial trabecular and cortical bone microarchitecture by high resolution peripheral quantitative computerised tomography at age 25. Serum 25-hydroxyvitamin D (25OHD) concentrations were measured at ages 8, 16 and 25. Multivariable linear regression was used to analyse the association of 25OHD concentrations at three timepoints with bone measures at ages 16 and 25. The proportion of participants with vitamin D deficiency (< 50 nmol/L) was 11%, 43% and 41% at three timepoints, respectively. Serum 25OHD concentrations at age 8 were not significantly associated with any bone measures at age 16 or 25. Serum 25OHD concentrations at age 16 had a significant association with higher BMD at nearly all sites at ages 16 and 25 as well as lower radial porosity and more compact trabecular microarchitecture (higher density, increased number and reduced separation) at both the radius and tibia at age 25. Serum 25OHD concentrations at age 25 were only associated with hip BMD. Higher vitamin D concentrations in adolescence, to a lesser extent at age 25, have beneficial associations with BMD and bone microarchitecture in early adulthood. Optimising vitamin D status particularly during adolescence should be a priority.