Dietary calcium and blood pressure: a review of the observational studies.

The objective of this study was to assess whether the epidemiological data support a relation between dietary calcium intake and blood pressure (BP). Fifty three published reports of observational studies relating intake of calcium or calcium-rich foods to BP in the USA (n = 33), Canada (n = 3), Puerto Rico (n = 1), Europe (n = 9), Asia (n = 5), Australia (n = 1) and South Africa (n = 1) were identified including a Medline search (January 1983-November 1993). Sample size ranged from 55 to over 58,000 (median 885). Five studies were prospective, 48 cross-sectional, of which four also contained a longitudinal component. Various dietary methodologies were used; the most common was the 24 h dietary recall. Most studies controlled for age, sex and body mass index, with variable control for other confounders. Many reports also allowed identification of subgroups by sex, age and race. One hundred and eight population samples and subgroups could then be identified. There was inconsistency in results both within and between studies. In 12 of the 53 published reports simple regression coefficients were reported. Median regression coefficients were -0.033 mm Hg/100 mg Ca (range -4.90 to +/- 0.47; n = 12) for systolic blood pressure (SBP) and -0.140 mm Hg/100 mg Ca (range -9.40 to +1.63; n = 10) for diastolic blood pressure (DBP). The association between dietary calcium intake and BP could not be assessed in all 108 population samples and subgroups because of design features, incompleteness of reported results and methods of analysis.(ABSTRACT TRUNCATED AT 250 WORDS)