This review did not find robust evidence that oral calcium supplementation reduces high blood pressure in adults. It reviewed 13 trials enrolling 485 people, which compared calcium supplementation with placebo or no treatment, and measured blood pressure 8 to 15 weeks later. On average, people receiving extra calcium achieved slightly lower systolic blood pressure at the end of trials. However, most trials were of poor quality, so their results may not be reliable. Trials were too small and short to measure whether extra calcium reduces the risk of death, heart attack or stroke. Calcium usually had no more adverse effects than placebo. Larger, longer duration, better quality trials are needed to clarify whether calcium supplementation can lower high blood pressure.
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Wprowadzenie
Metabolic studies suggest calcium may have a role in the regulation of blood pressure. Some epidemiological studies reported people with a higher intake of calcium tend to have lower blood pressure. Previous systematic reviews and meta-analyses reached conflicting conclusions about whether oral calcium supplementation can reduce blood pressure.
Cele
To evaluate the effects of oral calcium supplementation as a treatment for primary hypertension in adults.
Metody wyszukiwania badań
We searched the Cochrane Library, MEDLINE, EMBASE, Science Citation Index, ISI Proceedings, ClinicalTrials.gov, Current Controlled Trials, CAB abstracts, and reference lists of systematic reviews, meta-analyses and randomised controlled trials (RCTs) included in the review.
Kryteria doboru badań
Inclusion criteria were: 1) RCTs comparing oral calcium supplementation with placebo, no treatment, or usual care; 2) treatment and follow-up ≥8 weeks; 3) participants over 18 years old, with raised systolic blood pressure (SBP) ≥140 mmHg or diastolic blood pressure (DBP) ≥85 mmHg; 4) SBP and DBP reported at end of follow-up. We excluded trials where: participants were pregnant; received antihypertensive medication which changed during the study; or calcium supplementation was combined with other interventions.
Zbieranie i analiza danych
Two reviewers independently abstracted data and assessed trial quality. Disagreements were resolved by discussion or a third reviewer. Random effects meta-analyses and sensitivity analyses were conducted.
Główne wyniki
We included 13 RCTs (n=485), with between eight and 15 weeks follow-up. The results of the individual trials were heterogeneous. Combining all trials, participants receiving calcium supplementation as compared to control had a statistically significant reduction in SBP (mean difference: -2.5 mmHg, 95% CI: -4.5 to -0.6, I2 = 42%), but not DBP (mean difference: -0.8 mmHg, 95% CI: -2.1 to 0.4, I2 = 48%). Sub-group analyses indicated that heterogeneity between trials could not be explained by dose of calcium or baseline blood pressure. Heterogeneity was reduced when poor quality trials were excluded. The one trial reporting adequate concealment of allocation and the one trial reporting adequate blinding yielded results consistent with the primary meta-analysis.
Wnioski autorów
Due to poor quality of included trials and heterogeneity between trials, the evidence in favour of causal association between calcium supplementation and blood pressure reduction is weak and is probably due to bias. This is because poor quality studies generally tend to over-estimate the effects of treatment. Larger, longer duration and better quality double-blind placebo controlled trials are needed to assess the effect of calcium supplementation on blood pressure and cardiovascular outcomes.
