McCarron 1985

Methods	Randomised, double‐blind, placebo‐ controlled, cross‐over trial The trial was conducted in the United States of America.
Participants	32 normotensive subjects. Healthy volunteers with no signs of secondary hypertension. Age: between 21 and 70 years.
Interventions	Intervention group: 1000 mg a day of elemental calcium as the carbonate or citrate salt. Control group: placebo tablets. Trial duration: 8 weeks, or placebo.
Outcomes	Change in blood pressure
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Random assignment of participants was done separately in blocks by computer.
Allocation concealment (selection bias)	Low risk	Medications were pre‐packaged by randomisation number for each participant and dispensed every 2 weeks.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"Placebo tablets consisted of microcrystalline cellulose and starch and were identical in taste and appearance to the calcium carbonate tablets. Subjects and members of the investigative staff were blinded."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	"A Hawksley random‐zero sphygmomanometer (Hawksley & Sons, Ltd., Lancing, England) was used for measurement of blood pressure after the participant was supine for 5 minutes and after standing for 2 minutes."
Incomplete outcome data (attrition bias) All outcomes	Low risk	All 32 normotensive participants were reported in the results.
Selective reporting (reporting bias)	Low risk	Primary outcome result reported
Other bias	Low risk	The baseline characteristics were similar between the groups.