Lyle 1987.

Study characteristics
Methods	Randomised, double‐blind, placebo‐controlled trial The trial was conducted in the United States of America.
Participants	Normotensive male participants Ethnicity: Black (n = 21) and white (n = 54) Age: 19 to 52 years
Interventions	Internvention group: calcium, 1500 mg a day Control group: placebo "Participants were randomly assigned within racial groups to either treatment". Trial duration: 12‐week period
Outcomes	Blood pressure Serum levels of total and ionised calcium Total inorganic phosphorus Parathyroid hormone Overnight urinary electrolyte values
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described
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	Assignment was double‐blind. "Indistinguishable placebo tablets were composed of microcrystalline methylcellulose and starch".
Blinding of outcome assessment (detection bias) All outcomes	Low risk	"Use of a random‐baseline sphygmomanometer and blinded observers to eliminate bias during blood pressure measurement, documentation of nutrient intake other than the supplement, and control for body weight and other possible confounders"
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants randomised were included in the results.
Selective reporting (reporting bias)	Low risk	All outcomes were reported.
Other bias	Low risk	The groups were similar at baseline.