Safety of High-Dose Vitamin D Supplementation: Secondary Analysis of a Randomized Controlled Trial.

CONTEXT: More than 3% of adults report vitamin D intakes of 4000 IU/day or more, but the safety of this practice is unknown. OBJECTIVE: The objective of this work is to establish whether vitamin D doses up to 10 000 IU/day are safe and well tolerated. DESIGN: The Calgary Vitamin D Study was a 3-year, double-blind, randomized controlled trial. SETTING: A single-center study was conducted at the University of Calgary, Canada. PARTICIPANTS: Participants included healthy adults (n = 373) ages 55 to 70 years with serum 25-hydroxyvitamin D 30 to 125 nmol/L. INTERVENTIONS: Participants were randomly assigned 1:1:1 to vitamin D3 400, 4 000, or 10 000 IU/day. Calcium supplementation was initiated if dietary calcium intake was less than 1200 mg/day. MAIN OUTCOME MEASURES: In these prespecified secondary analyses, changes in serum 25-hydroxyvitamin D, calcium, creatinine, 24-hour urine calcium excretion, and incidence of adverse events were assessed. Between-group differences in adverse events were examined using incident rate differences and logistic regression. RESULTS: Of 373 participants (400: 124, 4000: 125, 10 000: 124), 49% were male, mean (SD) age was 64 (4) years, and 25-hydroxyvitamin D 78.0 (19.5) nmol/L. Serum calcium, creatinine, and 24-hour urine calcium excretion did not differ between treatments. Mild hypercalcemia (2.56-2.64 mmol/L) occurred in 15 (4%) participants (400: 0%, 4000: 3%, 10 000: 9%, P = .002); all cases resolved on repeat testing. Hypercalciuria occurred in 87 (23%) participants (400: 17%, 4000: 22%, 10 000: 31%, P = .01). Clinical adverse events were experienced by 365 (97.9%) participants and were balanced across treatment arms. CONCLUSIONS: The safety profile of vitamin D supplementation is similar for doses of 400, 4000, and 10 000 IU/day. Hypercalciuria was common and occurred more frequently with higher doses. Hypercalcemia occurred more frequently with higher doses but was rare, mild, and transient.

Methods and procedures for: A randomized double-blind study investigating dose-dependent longitudinal effects of vitamin D supplementation on bone health.

The optimum dose of vitamin D and corresponding serum 25-hydroxyvitamin D (25OHD) concentration for bone health is still debated and some health practitioners are recommending doses well above the Canada/USA recommended Dietary Reference Intake (DRI). We designed a three-year randomized double-blind clinical trial investigating whether there are dose-dependent effects of vitamin D supplementation above the Dietary Reference Intake (DRI) on bone health. The primary aims of this study are to assess, whether supplementation of vitamin D3 increases 1) volumetric bone mineral density measured by high-resolution peripheral quantitative computed tomography (HR-pQCT); 2) bone strength assessed by finite element analysis, and 3) areal bone mineral density by dual X-ray absorptiometry (DXA). Secondary aims are to understand whether vitamin D3 supplementation improves parameters of bone microarchitecture, balance, physical function and quality of life. Participants are men and women aged 55-70 years, with women at least 5-years post-menopause. The intervention is daily vitamin D3 supplementation doses of 400, 4000 or 10,000 IU. Participants not achieving adequate dietary calcium intake are provided with calcium supplementation, up to a maximum supplemental dose of 600 mg elemental calcium per day. Results from this three-year study will provide evidence whether daily vitamin D3 supplementation with adequate calcium intake can affect bone density, bone microarchitecture and bone strength in men and women. Furthermore, the safety of high dose daily vitamin D3 supplementation will be explored.