Epidemiologic association between dietary calcium intake and blood pressure: a meta-analysis of published data

The objectives of the study were to assess whether the epidemiologic data support a relation between dietary calcium intake and blood pressure, to obtain a quantitative estimate of the difference in blood pressure for a given difference in dietary calcium intake, and to assess the public health implications. A meta-analysis of published data (January 1983 to November 1993) that investigated the association between dietary calcium intake and blood pressure in different populations around the world was performed. Of 63 population studies identified, 23 were suitable for a quantitative overview (total n = 38,950). Unadjusted regression coefficients (95% confidence intervals) were obtained. Pooled unadjusted regression coefficients (95% confidence intervals) were then computed weighting each individual study by the inverse of its variance. Tests of heterogeneity and sensitivity analysis were carried out, and the possibility of publication bias was assessed. The regression coefficients ranged between -9.40 and 1.63 mmHg/100 mg calcium for systolic blood pressure and between -4.90 and 0.47 for diastolic blood pressure. In men (11 studies, n = 7,271), the pooled regression coefficients were -0.010 and -0.009 mmHg/100 mg calcium for systolic and diastolic pressures, respectively (p < 0.001 and p < 0.05). In women (six studies, n = 8,507), they were -0.15 and -0.057 mmHg/100 mg calcium (p < 0.001 and p < 0.02), and in men and women combined (six studies, n = 23,172 for systolic pressure and four studies, n = 3,215 for diastolic pressure) they were -0.061 and -0.061 mmHg/100 mg calcium (p < 0.001 and p < 0.05). In those studies that used the 24-hour recall method, the pooled regression coefficients were -0.06 and -0.09 mmHg/100 mg calcium (p < 0.005 and p = 0.07), whereas in those that used the food frequency questionnaire, they were -0.15 and -0.05 mmhg/100 mg calcium (p < 0.001 and p < 0.03). These data are consistent with an inverse association between dietary calcium intake and blood pressure. However, the size of the estimate, the observed heterogeneity among studies, and the possibility of confounding and publication bias indicate that an increase in calcium intake above the Recommended Dietary Allowance is not recommended at population level for the prevention and treatment of high blood pressure.