PTH and vitamin D deficiency: Additionally, a clinical trial [30] following men over an 8 year period, showed that for those with vitamin D deficiency (≤ 20 ng/mL), total BMD, cortical BMD, cortical area and cortical thickness measured using high-resolution pQCT at the distal radius all declined faster over time than for men with sufficient vitamin D. The study also reported that men in the two highest quartiles of parathyroid hormone had a faster decline in total BMD, cortical thickness, cortical area and cortical BMD at the distal radius than those in the lowest quartile of parathyroid hormone.