Johnson 1985.

Study characteristics
Methods	Randomised double‐blind clinical trial. Women were divided into a control and an experimental group in a double blind design. The trial was conducted in the United States of America.
Participants	81 normotensive and 34 medicated hypertensive women Age: between 35 and 65 years
Interventions	Intervention group: 3 daily tablets of a calcium carbonate supplement containing 500 mg calcium per tablet Control group: placebo tablets Trial duration: 4 years
Outcomes	Bone mineral content and blood pressure
Notes	Most of the women were using thiazides. "Dietary calcium of all women was determined using a precoded food record form, which had been tested for validity against weighed food intakes". This study was supported by Wisconsin Milk Marketing Board, Inc, Marion Laboratories, Kansas City, MO.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described
Allocation concealment (selection bias)	Unclear risk	Not described
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	"The original group of women, including the hypertensives, was divided into a control and an experimental group in a double‐blind design". However, methods were not described.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	"Blood pressure was measured from the right arm of seated participants using a standard mercury sphygmomanometer". Not reported if outcome assessors were blinded to the intervention
Incomplete outcome data (attrition bias) All outcomes	High risk	44 participants were randomised to the intervention and 41 were analysed. 51 participants were randomised to placebo and 40 were analysed.
Selective reporting (reporting bias)	Low risk	All primary outcomes were reported.
Other bias	Low risk	Baseline characteristics were similar between the groups.