LETTER
Dietary Calcium and Blood Pressure
Heiner C. Bucher, MD;
Gordon H. Guyatt, MD; and
Richard J. Cook, MD
15 March 1997 | Volume 126 Issue 6 | Page 492
TO THE EDITOR:
Allender and colleagues [1] investigated the relation of dietary calcium intake and blood pressure in a meta-analysis of randomized, controlled trials. They found that calcium supplementation decreased blood pressure by a greater amount in trials in which the mean blood pressure was greater than 130 mm Hg than in trials in which it was less than 130 mm Hg (change of –1.68 mm Hg [95% CI, –3.18 to –0.18 mm Hg] compared with change of –0.53 mm Hg [CI, –1.56 to 0.49 mm Hg]). We believe the inference that the hypotensive effect of calcium is greater in hypertensive persons is weak. Our reasons follow.
We published a systematic review on dietary calcium supplementation and blood pressure that included 33 randomized trials that had at least 2 weeks of calcium supplementation [2]. Our pooled estimate showed a change in systolic blood pressure of –1.27 mm Hg (CI, –2.25 to –0.29 mm Hg), very similar to the estimate found by Allender and colleagues ( –0.89 mm Hg [CI, –1.74 to –0.05 mm Hg]). As did Allender and colleagues, we found no effect of calcium supplementation on diastolic blood pressure.
Allender and colleagues did not test whether the difference between the trials in which mean blood pressure was higher and those in which it was lower was statistically significant. We went beyond the analyses of Allender and colleagues and studied the relation between baseline blood pressure and calcium supplementation by using regression analysis. The coefficient was (± SE) –0.013± 0.014 for systolic blood pressure and –0.010± 0.018 for diastolic blood pressure; the model explained a trivial and nonsignificant proportion of the variance (R2 values, 0.021 for systolic blood pressure and 0.007 for diastolic blood pressure). Our analysis avoids the arbitrary cut point chosen by Allender and colleagues and suggests that any apparent association may be explained by chance.
The hypothesis that the hypotensive effects of calcium are greater in hypertensive patients meets few, if any, of the criteria for a subgroup analysis [3].
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Author and Article Information
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Medizinische Universitats-Poliklinik, Kantonsspital, Basel, Switzerland
McMaster University, Hamilton, Ontario, Canada
University of Waterloo, Kitchener, Ontario, Canada
1. Allender PS, Cutler JA, Follmann D, Cappuccio FP, Pryer J, Elliot P. Dietary calcium and blood pressure: a meta-analysis of randomized clinical trials. Ann Intern Med. 1996; 124:825-31.
2. Bucher HC, Cook RJ, Guyatt GH, Lang JD, Cook DJ, Hatala R, et al. Effects of dietary calcium supplementation on blood pressure. JAMA. 1996; 275:1016-22.
3. Oxman AD, Guyatt GH. A consumer's guide to subgroup analysis. Ann Intern Med. 1992; 116:78-84.
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