Vitamin D and calcium, long recognized as important for bone health, have attracted clinical interest in recent years for their potential nonskeletal benefits, including cancer prevention. Despite this enthusiasm, however, few completed randomized clinical trials of supplemental vitamin D administered with or without calcium have examined cancer end points, and no previously completed trial has reported cancer as a primary prespecified outcome. Moreover, few randomized trials have tested high doses of vitamin D (ie, at least twice as high as the current recommended dietary allowance of 600-800 IU/d for bone health1) for effects on nonskeletal outcomes.
Manson JE, Bassuk SS, Buring JE. Vitamin D, Calcium, and CancerApproaching Daylight?. JAMA. 2017;317(12):1217-1218. doi:10.1001/jama.2017.2155