Interaction between Vitamin D Status and Calcium Intake in Association with Blood Pressure and Hypertension

Vitamin D deficiency and inadequate calcium intake are supposed to be potentially related to cardiovascular outcomes, however, their combined association with hypertension remains unclear. In this cross-sectional study among 2,352 subjects, dietary calcium intake was assessed by using a valid food frequency questionnaire, and serum 25-hydroxyvitamin D (25OHD) was measured by the Ultra Performance Liquid Chromatography system. Hypertension was defined as a level of systolic pressure ≥140 mmHg or diastolic pressure ≥90 mmHg, or both, or administration of antihypertensive medications. Vitamin D status was classified into deficiency (25OHD<20 ng/mL), insufficiency (20 ng/mL≤25OHD<30 ng/mL) and sufficiency (25OHD≥30 ng/mL), while dietary calcium intake was divided into tertiles as low, medium, and high. Two-way analysis of variance (ANOVA) and multivariable logistic regression models were adopted. A significant interaction between vitamin D status and dietary calcium intake in relations to systolic blood pressure (p=0.042) and hypertension (p=0.029) indicates the associations of dietary calcium intake with systolic blood pressure and hypertension depend on the vitamin D status, and vice versa. Only in the vitamin D deficiency group, dietary calcium intake was significantly associated with systolic blood pressure level (β=-0.162, p<0.001) and prevalence of hypertension (odd ratio=2.20, p<0.001). The significance was not substantially compromised after further adjustment for confounding factors. In conclusion, the combination of vitamin D deficiency and low dietary calcium intake, rather than alone, is associated with hypertension.