Calcium intake is inversely associated with peripheral blood pressure: possible interaction with serum calcium

Objective: Serum calcium has been directly associated with blood pressure (BP) level or the presence of hypertension in different observational studies, but the association between dietary calcium intake and BP remains unclear. The objective of this study is to investigate the relationship between calcium intake and BP in two large population-based studies. Design and method: Calcium intake and BP were evaluated in the Malmö Diet and Cancer (MDC) study (n∼28,000) in Sweden and the UK Biobank (n∼330,000) in the United Kingdom. Calcium intake in the MDC study was determined using a 7-day menu book for recording of meals that varies from day to day (usually lunch and dinner meals) and a 168-item diet questionnaire (“Kosthistoria”), combined with a 45–60 min diet history interview. In the UK Biobank food frequency was assessed using a dietary questionnaire based on a 24-hour dietary recall of the previous day. Results: In the MDC study, calcium intake demonstrated an inverse association with systolic (-0.564, 95% CI -0.784/-0.343) and diastolic BP (-0.326, 95% CI -0.444/-0.209) only when the values were not adjusted for total caloric intake. In the UK Biobank, higher calcium intake was associated with lower systolic and diastolic BP when adjusted for caloric intake, but only with diastolic BP when unadjusted for caloric intake. In the MDC, in the subsample of patients with measured serum calcium levels (n=4,095), we observed a positive association between serum calcium level and systolic BP. Upon comparing the association across quartiles of calcium intake, this association was evident only in the three lowest quartiles, while it became negative in the highest quartile. Conclusions: Calcium intake from diet tends to be linked with lower BP and appears to mitigate the positive association between serum calcium and BP. Further studies are required to confirm these associations and to explore whether there is an interaction with hormones that regulate calcium distribution in the body.