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Calcium supplementation for blood pressure



Clinical bottom line: Studies of relatively poor quality showed that dietary and nondietary calcium supplementation produced modest reductions in systolic and diastolic blood pressure in normotensive or mildly hypertensive patients. The risk of kidney stones should be considered.


Systematic review:

Griffith LE, Guyatt GH, Cook RJ, Bucher HC, Cook DJ. The influence of dietary and nondietary calcium supplementation on blood pressure. An updated metaanalysis of randomized controlled trials. AJH 1999; 12: 84-92.

Date review completed: May 1997

Number of trials included: 42

Number of patients: (2068 active; 2059 control; 433 patients in cross-over studies)

Control groups: no calcium, placebo.

Main outcomes: change in systolic and diastolic blood pressure (mm Hg).

Inclusion criteria were randomised controlled trial (RCT) which assessed the effect of calcium supplementation on blood pressure in nonpregnant normotensive or hypertensive individuals. Duration of treatment had to be more than two weeks and dose of calcium more than 1000 mg daily.

The Cochrane Collaboration search strategy, MESH terms and relevant key words were used to identify randomised trials and meta-analyses from MEDLINE (January 1993 to May 1997). No language restrictions were made, bibliographies of retrieved reports were checked and unpublished information was sought from experts. If necessary additional information was sought from authors. Quality assessments were made. Pooled data was assessed using a random effects model to calculate effect size with 95% confidence intervals and heterogeneity was tested.


Findings:

Blood pressure was assessed in either the sitting, standing, supine or lateral position. Study duration mainly varied between 4-14 weeks; eight had an intervention period of more than six months. Mean baseline values for systolic pressure ranged between 102-166 mm Hg and for diastolic pressure ranged between 58-98 mm Hg. Nine trials assessed dietary supplements (lactovegetarian or lacto-ovo-vegetarian versus omnivorous diet; low versus dairy product rich diet; diet with dairy-products versus diet mineral-poor in dairy products). There was no significant difference in reduction in blood pressure with the different dietary supplements. Thirty-three RCTs assessed nondietary calcium supplementation (e.g. calcium carbonate).

The majority of studies showed a reduction in blood pressure with calcium supplementation for both dietary and nondietary supplementation. When information was pooled for all studies the mean reduction in systolic blood pressure was 1.44 (2.2 to 0.68) and for diastolic blood pressure it was 0.84 (1.44 to 0.24). Dietary supplementation produced slightly, but not significantly better reductions in both diastolic and systolic blood pressure than nondietary supplementation.


Adverse effects

The reviewers' did not mention whether the individual trials reported adverse effects, but did note that kidney stone formation is the most obvious adverse effect associated with calcium intake.

 

Comment

The reviewers' concluded that the slight reductions in blood pressure seen with calcium supplementation do not justify its use as a sole treatment for mild hypertension. They failed to mention whether the individual trials included in the systematic review were blinded. If not this could have led to observer bias. With the exception of two, the studies were small. Sixty-six percent of dietary studies and 58% of nondietary studies had fewer than 25 patients per group. The methodological quality of the trials was relatively poor. Only 16/42 (38%) studies had quality scores greater than three using a seven point scoring system (numbered 0-6).

Further reading


Related topics

Identifier

AT055 - 6034 CALCIUM SUPPLEMENTATION FOR BLOOD PRESSURE: Aug-2000