Cutler 1992

Methods	Randomised double‐blind clinical trial.
Participants	Healthy subjects. with high‐normal diastolic blood pressure, not taking antihypertensive drugs, not grossly obese (BMI < 36.15 kg/m*), and not consuming more than 21 alcohol‐containing drinks weekly. Intervention group: 237 participants assigned to receive calcium. Control group: 234 participants assigned to receive placebo. Gender: Men and women. Age: 30 to 54 years. Exclusion criteria included pre‐existing cardiovascular or life‐threatening conditions, conditions requiring or contraindicating any of the study interventions, and intent to become pregnant during the study period. Age average: 43 years; 69% were men, 86% were white, and 51% had completed college. Baseline blood pressures averaged 125/84 mm Hg and BMI averaged 27.3 kg/m2. Dietary calcium intake: average 970 mg.
Interventions	Calcium supplementation vs placebo tablets. Intervention group: calcium carbonate representing calcium, 25 mmol or 1.0 g (2 pills per day). Control group: placebo tablet. Trial duration: 6 months.
Outcomes	Primary: "change in diastolic blood pressure from baseline to final follow‐up." Secondary: "changes in systolic blood pressure and intervention compliance measures."
Notes	Dietary calcium intakes according to the food frequency questionnaire data averaged 970 mg.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation lists were computer‐generated at the TOHP Data Coordinating Center.
Allocation concealment (selection bias)	Low risk	Randomisation assignments were obtained from the coordinating centre by telephone when possible, otherwise sealed opaque envelopes were used to convey the treatment assignment. Adherence to the appropriate assignment sequence was monitored by the coordinating centre.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double‐blind fashion, with placebo controls
Blinding of outcome assessment (detection bias) All outcomes	Low risk	"Trained, certified observers who were blinded to participants' treatments. Blood pressure was measured with a Hawksley random‐zero sphygmomanometer."
Incomplete outcome data (attrition bias) All outcomes	Low risk	Blood pressure data were complete for 95% of participants at 3 months and 93% at 6 months. Pill counts were obtained for 91% at 6 weeks, 90% at 3 months, and 84% at 6 months.
Selective reporting (reporting bias)	Low risk	There is no evidence of selective reporting.
Other bias	Low risk	Baseline characteristics were similar.