Current issues of ACP Journal Club are published in Annals of Internal Medicine


Therapeutics

A low-sodium, high-potassium, high-magnesium salt lowered blood pressure

ACP J Club. 1995 Jan-Feb;122:3. doi:10.7326/ACPJC-1995-122-1-003


Source Citation

Geleijnse JM, Witteman JC, Bak AA, den Breeijen JH, Grobbee DE. Reduction in blood pressure with a low sodium, high potassium, high magnesium salt in older subjects with mild to moderate hypertension. BMJ. 1994 Aug 13;309:436-40.


Abstract

Objective

To evaluate the effectiveness of a low-sodium, high-potassium, high-magnesium salt in lowering blood pressure (BP) in older patients with mild-to-moderate hypertension.

Design

Randomized, double-blind, placebo-controlled trial with 24-week follow-up and a reassessment of BP 25 weeks after the intervention.

Setting

Population-based study in a suburb of Rotterdam, the Netherlands.

Patients

100 patients aged 55 to 75 years (mean age 66 y, 51 men) with untreated mild-to-moderate hypertension (systolic BP between 140 mm Hg and 200 mm Hg or diastolic BP between 85 mm Hg and 110 mm Hg). Exclusion criteria were history of myocardial infarction, angina pectoris, diabetes mellitus, or impaired renal function; or consumption of a salt-restricted diet on medical advice. 97 patients completed the study.

Intervention

49 patients received a mineral salt (sodium:potassium:magnesium, 8:6:1 mmol) for use in cooking and at the table and received foods prepared with the mineral salt for 24 weeks. 51 patients received common salt and food prepared with common salt for 24 weeks. The foods provided an estimated 57% of the salt intake for an older Dutch population.

Main outcome measures

BP, pulse rate, body weight, and urinary sodium and potassium excretion.

Main results

The mean of measurements at weeks 8, 16, and 24 showed that systolic BP fell by 7.6 mm Hg (95% CI 4.0 to 11.2 mm Hg, P < 0.001) and that diastolic BP fell by 3.3 mm Hg (CI 0.8 to 5.8 mm Hg, P < 0.001) in the mineral salt group compared with the common salt group. The decrease in BP was of the same magnitude for men and women and was not modified by age. The 24-hour sodium excretion decreased by a mean of 38.4 mmol (CI 24.0 to 52.8 mmol, P < 0.001), and potassium excretion increased by 17.5 mmol (CI 7.9 to 27.0 mmol, P < 0.001) in the mineral salt group compared with the common salt group. Changes in pulse rate and body weight were not significantly different between the groups. 25 weeks after the intervention period, with all participants on an ad libitum common salt diet, the BP difference between the groups was no longer detectable.

Conclusion

A low-sodium, high-potassium, high-magnesium mineral salt lowered blood pressure in older patients with untreated mild-to-moderate hypertension.

Sources of funding: Akzo Nobel and the Rotterdam Medical Research Foundation (ROMERES).

For article reprint: Mrs. J.M. Geleijnse, Department of Epidemiology and Biostatistics, Erasmus University Medical School, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands. FAX 31-317-403342.


Commentary

Most trials to lower BP by nonpharmacologic means have focused on a single intervention (e.g., reduced salt intake, increased calcium ingestion, weight reduction). The study by Geleijnse and colleagues combined 3 interventions by reducing sodium and increasing potassium and magnesium intake. The "instrument" of dietary change was a natural mineral salt from Iceland, arguably more palatable than other salt substitutes. The magnitude of BP reduction in this study was equal to that in most other studies of nonpharmacologic interventions.

Unfortunately, the field of dietary intervention for BP control has conflicting data. Although decreased salt ingestion or increased potassium, calcium, or magnesium intake improved BP control in some studies (1, 2), equally well-done studies do not support those findings (3, 4). Reflecting this lack of consensus, the Joint National Committee V report (5) was only lukewarm in its support of salt reduction or of potassium and calcium increase. An emerging dietary approach suggests that combined interventions may result in enhanced control.

The allure of a nonpharmacologic approach is great, especially in older persons who are liable to have drug interactions and side effects and who are concerned about the cost of drugs. But a dietary approach is not without drawbacks: Foods may be considered unpalatable, and supplements are costly and may cause side effects such as gastrointestinal distress.

The control group in the study actually had an increase in urinary sodium excretion and a decrease in potassium excretion during the trial (itself an intervention). Overall, however, the study was well done and, if confirmed by additional work, could represent a welcome advance.

Bruce E. Johnson, MD
University of Kansas Medical CenterKansas City, Kansas, USA


References

1. Stamler J, Rose G, Stamler R, et al. INTERSALT study findings. Public health and medical care implications. Hypertension. 1989;14:570-7.

2. Cappuccio FP, MacGregor GA. Does potassium supplementation lower blood pressure? A meta-analysis of published trials. J Hypertens. 1991;9:465-73.

3. Collaborative Research Group. The effects of nonpharmacologic interventions on blood pressure of persons with high normal levels. Results of the Trials of Hypertension Prevention, Phase I. JAMA. 1992;267:1213-20.

4. Ferrara LA, Iannuzzi R, Castaldo A, et al. Long-term magnesium supplementation in essential hypertension. Cardiology. 1992;81:25-33.

5. Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (JNC V). The fifth report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure. Arch Intern Med. 1993;153:154-83.