We assessed the frequency of hypercalcemia in hydrochlorothiazide users in a post hoc analysis of a randomized , double-blind , dose-finding trial of 328 blacks ( median age 51 years ) assigned to either placebo , or 1000 , 2000 , or 4000 international units of cholecalciferol ( vitamin D3 ) daily for 3 months during the winter ( 2007-2010 ) .