The study team gave 52 people 1,000 mg doses of calcium and vitamin D either 30 minutes before or 1 hour after exercising. Among those who took the supplements before working out, one important measure of bone loss improved, according to the findings presented last week at the annual meeting of the Endocrine Society. These findings piggyback on another University of Colorado study, published last year by member of the same research team, that found 1,000 mgs of calcium slowed bone deterioration by 33% compared to a placebo.