Plain language summary:

Review question

We wanted to find out the effects of calcium intake on blood pressure in people with normal blood pressure. 

Background

Hypertension is a serious health problem that increases the risk of heart and kidney diseases. Several studies have shown that increasing calcium intake lowers blood pressure even in individuals within a normal blood pressure range. Increasing calcium intake also has benefits for pregnancy outcomes, effects which are thought to be mediated also by blood pressure reduction. High blood pressure has been identified as a major risk factor for mortality and even small reductions in blood pressure can decrease the occurrence of coronary artery disease, stroke and death. 

Study characteristics

We selected studies that assessed the effect of dietary calcium interventions such as supplementation or food fortification on blood pressure in normotensive people of all ages. Searches were last run in September 2020. 

Key findings

This review analysed information from 20 trials of which 18 trials (3140participants) provided date for the effect of the intervention. We found that an increase in calcium intake slightly reduces both systolic and diastolic blood pressure by 1.37 mmHg lower and by 1.45 mmHg lower, respectively. This effect was higher with doses of calcium above 1000 mg/day. Systolic blood pressure was reduced by 1.05 mmHg with doses of calcium 1000 to 1500 mg/day and by 2.79 mmHg with doses of calcium equal to or over 1500 mg/day. 

We noted a reduction in blood pressure in both men and women and at ages from 11 to 82 years old, but the reduction was greater among younger people. Systolic blood pressure was reduced by 1.86 mmHg among those less than 35 years and by 0.97 mmHg among those 35 years or older. 

None of the studies reported adverse events. We need further research to determine the ideal dosage of supplementation and whether it is more effective and safer as part of the diet or as a supplement. 

Quality of the evidence

We found high quality of evidence for systolic and diastolic blood pressure in both men and women. The quality of evidence was also high for participants 35 years or older and moderate for younger people. The quality of evidence was high for doses of calcium of 1000 to 1500 mg/day and was moderate for lower or higher doses. 

Five of the 18 trials were industry funded.

Read the review: Calcium supplementation for prevention of primary hypertension