Twenty-nine RCTs (n=1,410) were included. The follow-up ranged from 1 week to 4 years. Thirteen trials studied normotensive participants (n=963) and 16 studied hypertensive participants (n=447); of these, 3 trials studied both normotensive and hypertensive patients.
Normotensive persons: only 2 out of 13 trials demonstrated a significant decrease in both systolic and diastolic blood-pressure. Four trials demonstrated a significant effect for either systolic or diastolic blood-pressure, but not both. The remaining 7 trials failed to show either a significant beneficial effect or direct association between calcium intake and blood-pressure.
Hypertensive persons: 1 of the 16 studies demonstrated a significant decrease (p=0.01) in both systolic and diastolic blood-pressure, 2 papers had mixed results, and 13 reported no significant reductions in blood-pressure.
Pooled results: data were pooled from 28 arms or strata from 22 trials (n=1,231; normotensive persons, n=835; hypertensive persons, n=396). The weighted average changes in blood-pressure for normotensive and hypertensive participants combined were -0.89 mmHg (95% confidence interval, CI: -1.74, -0.05) and -0.18 mmHg (95% CI: -0.75, 0.40) for systolic and diastolic blood-pressure, respectively. Excluding the largest trial, which reported negative findings, did not change the results.
Pooled data for normotensive participants alone showed a systolic blood-pressure change of -0.53 mmHg (95% CI: -1.56, 0.49) and a diastolic blood-pressure change of -0.28 mmHg (95% CI: -0.99, 0.42); for hypertensive persons these were -1.68 mmHg (95% CI: -3.18, -0.18) and 0.02 mmHg (95% CI: -0.96, 1.00), respectively.
No consistent associations between the effect of calcium on blood-pressure and age, sex, calcium dose, or trial duration were demonstrated, although there was a significant negative correlation between systolic blood-pressure and age, and a significant positive correlation between systolic blood-pressure and the percentage of men studied.