Am Fam Physician. 2003 Jan 15;67(2):410-413.
Most patients with hypertension are advised to reduce dietary salt intake, yet this advice is largely based on short-term trials with diverse methodologies and outcomes. Hooper and colleagues systematically reviewed evidence for the benefit of salt restriction in reducing cardiovascular events and death in patients with hypertension.
The authors searched multiple electronic and other sources for relevant trials. The desired outcome measures were mortality and cardiovascular events, blood pressure, urinary sodium excretion, use of antihypertensive medication, and quality-of-life measures.
The final analysis included three trials with a total of 2,326 normotensive patients, five trials with a total of 387 patients with untreated hypertension, and three trials with a total of 801 treated patients with hypertension. Follow-up periods ranged from six months to seven years, and the outcomes assessed varied between trials. The largest and best-quality trials included intensive behavioral interventions. Blood pressures were reduced by an average of 1.1 to 2.5 mm Hg systolic and 0.6 to 1.2 mm Hg diastolic, depending on the length of follow-up. Urinary 24-hour excretion of sodium was 35.5 mEq per 24 hours (35.5 mmol per day). The degree of sodium intake reduction did not correlate with blood pressure reduction.
Studies differed in methods of assessment and reporting of adverse outcomes. Only 17 deaths were reported in the review period. These were equally distributed between intervention and control patients, and all deaths could not be attributed to cardiovascular causes. The studies used varying quality-of-life measures. Drop-out rates were similar in the intervention and control groups. Studies differed in dietary restrictions and reported rates between 13 and 69 percent for patient problems with the dietary recommendations.
The authors conclude that intensive interventions produce modest reductions in blood pressure but large changes in sodium excretion. The effect on cardiovascular events and mortality is not apparent from the research. The authors argue that the studies done to date are not helpful in the care of individual patients. In general, manipulation of dietary salt may help maintain blood pressure control in treated patients with hypertension but may have adverse effects on overall health.
Hooper L, et al. Systematic review of long term effects of advice to reduce dietary salt in adults. BMJ. September 21, 2002;325:628–32.
editor'S NOTE: Buried in the discussion of this article is the comment that cohort studies have associated low salt intake with increased total mortality and more cardiovascular events, except in obese people, in whom the effect is reversed. Subspecialists tell me that the treatment of hypertension is undergoing revolutionary changes, with experts split between conventional approaches and treatment directed by the patient's rennin status. It is prudent to remember that hypertension itself is a clinical sign and could be a signal of multiple pathophysiologic processes. In each patient, a completely different mechanism might be leading to the blood pressure reading. In the future, we may focus more on specifying the cause of hypertension than on juggling treatments. We live in hope of more logical and precise therapy for each patient. In the meantime, perhaps I will lighten up a bit on the salt advice to patients who already have enough to worry about.—a.d.w.
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