Barger‐Lux 2005.

Study characteristics
Methods	Randomised, double‐blind, placebo‐controlled, parallel‐group trial (2 groups) Duration of study: May 1995 to April 2000 Duration of follow‐up: 36 months
Participants	Setting characteristic: open population Inclusion criteria: healthy women, non‐smoking, non‐pregnant Exclusion criteria: height and weight that yielded a BMI > 30 kg/m2, binge‐drinking, significant risk of pregnancy, or more than occasional use of calcium supplements or calcium‐containing antiacids Age: 23.1 (SD 2.7) years Sample: Total included 152 (and total report of 87 followed at 36 months) (total of both groups not specified by group) Calcium group: 81 (baseline), 77 (2 months), and 67 (12 months) Placebo group: 71 (baseline), 69 (2 months), and 54 (12 months) Country: USA
Interventions	Comparison: calcium versus placebo Intervention group: calcium carbonate 500 mg 3 capsules (1500 mg) Control group: placebo capsules identical in appearance. Administration: daily consumption of food Duration of treatment: 36 months
Outcomes	BMD: total hip and lumbar spine BMC: total body, spine L1–L4, and total hip Biomarkers: serum calcium, urine calcium
Notes	Other intervention: (quote) "All participants were also supplied with fully‐labeled Geritol® multivitamin tablets, to be taken once daily to ensure at least minimal status for vitamin D and other trace nutrients. Ca, placebo, and multivitamin tablets were supplied without charge by the manufacturer (SmithKline Beecham)."
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not specified. Quote: "152 were randomly assigned to groups and entered the study."
Allocation concealment (selection bias)	Low risk	Central allocation (pharmacy‐controlled) and sequentially numbered drug containers.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "Tablets were packaged in bottles of 90 by the manufacturer; a research pharmacist selected and labeled the bottles."
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not specified.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Study authors reported withdrawals in both groups and the reasons were not related to the intervention. At 12 months, data for 10 (12%) participants in calcium group and 21 (21%) participants in placebo group were missing. The reported reasons were pregnancy, unwillingness to follow protocol, loss of follow‐up, and others.
Selective reporting (reporting bias)	Unclear risk	Not specified.
Other bias	Low risk	Baseline imbalance. Characteristics were imbalanced between groups. Quote: "The 2 groups were well matched except for urine calcium, which was significantly higher at baseline in those assigned to calcium (0.092 ± 0.007 g/g) than in those assigned to placebo (0.073 ± 0.005 g/g)." Comment: we judged this difference was not important in the study population.