The relation between free 25OH Vitamin D and vascular health indices has been studied by one group.

• ASHRAF A.P. (2014)

Associations between Vascular Health Indices and Serum Total, Free and Bioavailable 25-Hydroxyvitamin D in Adolescents

PLoS ONE 9(12): e114689.doi:10.1371/journal.pone.0114689

http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0114689&type=printable