Belizan 1983

Methods	Randomised double‐blind clinical trial. " The trial was conducted in Guatemala.
Participants	57 subjects (28 men and 29 women). Age:18 and 35 years. Healthy subjects not receiving medical treatment, women were not using hormonal contraceptives. Subjects .. "were free of diseases as assessed by a comprehensive clinical examination and blood and urine tests."
Interventions	Calcium supplementation vs placebo tablets. Intervention group: daily oral tablet containing 0.8 gms of calcium carbonate and 5.23 gms of calcium lactate gluconate (Calcium‐Sandoz, 1,000 mg), representing 1 gm of elemental calcium. Placebo group: daily oral tablet of the same weight, size, and organoleptic characteristics as the calcium tablet. Trial duration: 22 weeks.
Outcomes	Systolic blood pressure: read when the appearance of the first Korotkoff's sound occurred; Diastolic blood pressure: taken at the disappearance of the fifth Korotkoff's sound. The final value and SD were calculated from the reported basal blood pressure values and the percent changes between basal values and stable period (weeks 9 through 23) reported in the article. Blood levels of total calcium and magnesium by atomic absorption spectrophotometry Blood levels of inorganic phosphate by spectrophotometry Blood levels of albumin by dye‐binding bromocresol purpose Total calcium intake: basal dietary intake measured by 24 hr. food record plus compliance with supplementation
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	A computer random number generator was used. Participants were randomly assigned to 2 treatment groups. "Separate randomisation schedules were used for sex and age groups (18 ‐ 23 years and 24 ‐ 35 years)."
Allocation concealment (selection bias)	Low risk	Sequentially‐numbered containers were similar for both types of tablets, and a key number indicated the composition
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"The placebo group received a daily tablet of the same weight, size, and organoleptic characteristics as the calcium tablet." The treatment assignment was made double‐blind. The composition of the tablet unknown to participants or to the professional in charge of the examinations.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Composition of the tablet was unknown to participants or to professional in charge of the examinations or BP measurements.
Incomplete outcome data (attrition bias) All outcomes	High risk	28 men and 29 women were randomised to the study groups and 23 men and 20 women completed the study.
Selective reporting (reporting bias)	Low risk	All primary outcomes addressed.
Other bias	Low risk	No differences between groups were found in the variables collected during the baseline period except for systolic BP in the dorsal position among the men.