Billington EO, Burt LA, Rose MS, et al. - In this investigation involving healthy adults (n = 373), aged 55 to 70 years, with serum 25-hydroxyvitamin D 30 to 125 nmol/L, experts aspired to explore if vitamin D doses up to 10,000 IU/day are well tolerated and safe. This investigation was carried out at the University of Calgary, Canada. Participants in the study were randomly assigned 1:1:1 to vitamin D3 400, 40,000, or 10,000 IU/day. Calcium supplementation was started if the dietary calcium intake was less than 1,200 mg/day. Using incident rate differences and logistic regression, between-group differences in adverse events were examined. According to results, serum calcium, creatinine, and 24-hour urine calcium excretion did not vary between treatments. Vitamin D supplementation's safety profile is comparable for the 400, 4,000, and 10,000 IU/day doses. Hypercalciuria was common and occurred more often at higher doses. At higher doses, hypercalcemia occurred more frequently but was rare, mild, and transient.