Lyle 1992.

Study characteristics
Methods	Randomised, double‐blind, placebo‐controlled trial The trial was conducted in the United States of America.
Participants	42 adults Gender: men and women High normal or mildly hypertensive levels of blood pressure
Interventions	Intervention group: 500 mg of elemental calcium as calcium carbonate tablets Control group: placebo tablets Trial duration: 8 weeks
Outcomes	Blood pressure
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Participants were given a random number of calcium or placebo tablets.
Allocation concealment (selection bias)	Low risk	The supplements were strip‐wrapped individually and coded by someone not involved in the research study. The participants did not know which group they were assigned to, and the researcher(s) who collected other information also were not aware of the group assignment. Early analyses were completed prior to revealing the assigned groups as well.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Experimental group assessment was double‐blind. Tablets contained 500 mg of elemental calcium in the form of calcium carbonate. Indistinguishable placebo tablets
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Measurements were taken with a random‐zero sphygmomanometer at least 1 minute apart.
Incomplete outcome data (attrition bias) All outcomes	Low risk	44 men and women participants were randomised, 2 participants withdrew due to appointment conflicts and 42 participants completed the study. Missing outcome data balanced in numbers across intervention groups
Selective reporting (reporting bias)	Low risk	All outcomes were reported.
Other bias	High risk	In the treatment group, there were more men than in the placebo group. 8 of the 10 women were allocated to the placebo group. However, blood pressure measurements showed no statistically significant differences between groups.