Sacks 1998

Methods	Randomised, double blind parallel group trial. The trial was conducted in the United States of America.
Participants	321 participants 93% completed baseline and midpoint measurements. "Exclusion criteria included reported diastolic blood pressure 65 mm Hg; hypertension; BMI > 32 kg/m²; insulin‐dependent diabetes; cardiovascular disease; renal failure; medications that affect blood pressure, weight loss diets, use of nutritional supplements of calcium, magnesium, or potassium (including antacid preparations)."
Interventions	Intervention group: calcium carbonate 1200 mg daily (Caltrate 600 mg twice daily, Lederle Laboratories). Control group:identical placebo. Trial duration: 16 weeks. "The placebo group received twice the number of participants as the four treatment groups to improve statistical power."
Outcomes	Ambulatory 24‐hour blood pressure 24‐hour urine Body weight Health and side effects questionnaire Pill counts
Notes	Participants who had baseline systolic blood pressure above 160 mmHg or diastolic blood pressure above 95 mm Hg were excluded and advised to see their physicians.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	The randomisation was performed by a computer programme directed by the statistician on the project. The statistician had no contact with the data collectors or the participants. (Information provided by the author)
Allocation concealment (selection bias)	Unclear risk	Not described
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Participants were under double‐blind conditions for 16 weeks but methods not describe. The participants were not informed about their specific supplement group.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	The blood pressure machine automatically entered the blood pressure data on computer tape that was later converted to an ASCII file at the study office.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	321 participants were randomised. 300 participants were available for follow‐up measurements and 290 completed the study measurements.
Selective reporting (reporting bias)	Low risk	Primary outcome reported.
Other bias	Low risk	Baseline characteristics were similar.