Effect of dietary calcium and vitamin D supplementation on blood pressure control following salt loading

Epidemiological and animal studies assert an inverse relationship between calcium intake and risk of clinical hypertension. Nonetheless, there is a paucity of information on the effect of calcium and vitamin D co-administration on sodium chloride (NaCl)-induced blood pressure (BP) elevation in apparently healthy normotensive subjects. Hence, this study evaluated this relationship. For a 5-day study period, a group of 10 subjects (Group A) was placed on placebo while another group of 5 subjects (Group B) had dietary NaCl (200 mmol/day) and a third group of 5 subjects (Group C) had dietary NaCl (200 mmol/day) with calcium/vitamin D supplement (625 mg/200 IU). Before and after the 5-day regimen, blood pressure (BP) was measured, and blood, as well as urine samples, were collected from the subjects for evaluation of electrolyte status. Mean arterial BP (MABP) increased (p<0.01) in group B, but decreased in group C (p<0.01). Plasma potassium level increased in both groups B and C (p<0.01). However, while plasma calcium decreased in the two groups (p<0.01), plasma sodium decreased (p>0.01) only in group C, after the 5-day regimen. Urinary excretion of calcium increased and decreased (p<0.01) in groups B and C, respectively, a converse of the trend in urinary potassium. Whereas that of sodium increased in both groups B and C (p<0.01). These results suggest that oral Ca and Vitamin D supplementation may prevent a rise in BP in subjects on a high NaCl diet by attenuating plasma Na retention, with an augmented urinary excretion.