WHI 2006.

Study characteristics
Methods	Double‐blind trial. No details on method of randomisation Completed for fracture data 33751 of 36282
Participants	Community‐based women, USA 36,282 participants (all women), mean age 62.4 (SD 7.0) years Inclusion criteria: 50 to 79 years, no medical condition associated with predicted survival of less than 3 years Disease exclusions: hypercalcaemia, renal calculi Drug exclusions: corticosteroid use, calcitriol use, calcium supplements > 1000 mg/day, vitamin D > 600 IU/day (> 1000 IU/day after 1999)
Interventions	1. 1000 mg calcium as calcium carbonate and 400 IU vitamin D3 as 2 tablets daily Randomised 18176, 93% completed 7 (SD 1.4) years 2. 2 placebo tablets daily Randomised 18106, 93% completed 7 (SD 1.4) years Duration of treatment 7 (SD 1.4) years
Outcomes	Measured over a follow‐up of 7 years 1. Number of persons with new hip fracture 2. Number of persons with new clinical vertebral fracture 3. Number of persons with all new fractures (excluding rib, sternum, skull, face, finger, toe, cervical vertebral fracture) 4. Number of persons with gastrointestinal adverse events, renal calculi 5. Number of persons dying 6. Subgroup of 448 had 25(OH)D measured at 2 years
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	States "randomly assigned", no other information provided
Allocation concealment (selection bias)	Unclear risk	States "randomly assigned", no other information provided