?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.au=Berry%2C+DJ&rft.aufirst=DJ&rft.aulast=Berry&rft.title=PLoS+One&rft.pages=-&rft.issn=1932-6203&rft.issue=5&rft.atitle=Evaluation+of+genetic+markers+as+instruments+for+Mendelian+randomization+studies+on+vitamin+D.&rft.volume=7&rft.date=21+May+2012&rft.genre=article