Low-Salt Diet Shakes Off Heart Disease
By Crystal Phend, Staff Writer, MedPage TodayReviewed by Zalman S. Agus, MD; Emeritus Professor at the University of Pennsylvania School of Medicine.
April 20, 2007
Add Your Knowledge™ Additional Prevention Coverage
Deepak Bhatt, M.D.
Cleveland Clinic
BOSTON, April 20 -- The low-sodium diet may have been validated as a direct route to prevention of heart disease, according to investigators here.
The connection between a low-sodium diet and prevention of heart disease has been long suspected but never nailed down.
Prehypertensive patients who reduced salt intake 25% to 35% had 25% to 30% less cardiovascular event risk over the subsequent 10 to 15 years, reported Nancy R. Cook, Sc.D., of Brigham and Women's Hospital here, and colleagues online in the BMJ. Action Points
Explain to interested patients that the study confirms a clinical outcome benefit from a low-salt diet and weight reduction.
The American Heart Association recommends a daily salt intake below 2,300 mg for most people.
\"Results of our follow-up study reinforce recommendations to lower dietary sodium intake as a means of preventing cardiovascular disease in the general population,\" they wrote, and \"should dispel any residual concern that sodium reduction might be harmful.\"
Recommendations for salt reduction have relied primarily on clinical trial evidence of blood pressure reduction. Few observational studies and only limited and inconclusive trial data existed on cardiovascular outcomes.
Because of this, some had suggested that a low-salt diet could actually have an adverse effect on the heart, said Jeffrey Cutler, M.D., project director of the studies for the National Heart, Lung, and Blood Institute and a co-author on the paper.
To conclusively answer such questions, the researchers followed 2,415 patients from two earlier salt-reduction studies, phase I and II of the Trial of Hypertension Prevention.
The first tested a variety of lifestyle interventions over 18 months. The follow-up study included only the 417 usual-care control group participants and 327 randomized to a sodium reduction intervention consisting of dietary and behavioral counseling.
The second trial tested the effects of weight loss and sodium reduction over a three to four year period. It randomized 1,191 to usual care with or without weight loss intervention and the same number to a sodium reduction intervention similar to that in the first trial with or without weight loss intervention.
Both trials originally enrolled patients ages 30 to 54 with high-normal blood pressure defined as mean diastolic blood pressure 80 to 89 mm Hg in one and 83 to 89 mm Hg diastolic and less than 140 mm Hg systolic in the other. Participants were not taking antihypertensive medication.
Both found originally found small but significant blood pressure effects from sodium reduction.
The observational follow-up study began about 10 years after the first and five years of the second study ended, and lasted for about four years. Patients were sent questionnaires or reached by telephone to determine all cardiovascular events occurring after the end of the trials. Additional questionnaires were sent to responders every two years.
The primary outcome measure of cardiovascular disease included myocardial infarction, stroke, coronary artery bypass graft, percutaneous transluminal coronary angioplasty, and death with a cardiovascular cause.
Among the 2,415 total participants with follow-up outcome information obtained (77%), the findings were:
A 25% reduction in risk of cardiovascular disease among sodium reduction groups versus controls after adjustment for clinic site, demographics, and randomization to weight- loss intervention (relative risk 0.75, 95% confidence interval 0.57 to 0.99, P=0.04).
A 30% reduction in risk of cardiovascular disease with sodium reduction after additional adjustment for baseline weight and sodium excretion (RR 0.70, 95% CI 0.53 to 0.94, P=0.02).
Attenuation of the effect of sodium reduction with further adjustment for weight change during the trials (RR 0.74, 95% CI 0.55 to 1.01, P=0.06).
A similar but nonsignificant benefit of salt reduction excluding revascularization events (RR 0.72, 0.50 to 1.03, P=0.07).
\"That's about what one might expect from a moderate dose of a statin,\" Dr. Cutler said.
Mortality showed an effect in the same direction, though the study was not powered to show a difference in mortality, particularly in this group of patients at relatively low risk of death, Dr. Cutler said.
In a full intent-to-treat analysis of 3,126 participants with mortality data, the sodium intervention groups had 20% lower mortality risk (35 versus 42 deaths, RR 0.80, 95% CI 0.51 to 1.26, P=0.34). Cardiovascular disease-related mortality was likewise lower with sodium reduction (10 versus 15 deaths, RR 0.62, 95% CI 0.28 to 1.40, P=0.25).
Responses on the final questionnaire of the follow-up study also suggested that the original sodium-reduction interventions were effective long-term. Patients who reported a cardiovascular disease diagnosis were excluded from this analysis to reduce bias.
For the intervention group compared with controls, these results were:
Significantly more reported liking low-sodium or unsalted foods (71% versus 64%, P=0.003).
Significantly more reported usually or always using low sodium products (47% versus 29%, P<0.001).
Significantly more reported reading food labels for sodium content (66% versus 44%, P<0.001).
Significantly more reported keeping track of their daily sodium intake at least sometimes (28% versus 20%, P<0.001).
\"Despite its relatively small size as a trial of clinical outcomes, it provides some of the strongest objective evidence to date that lowering sodium intake, even among those without hypertension, reduces the risk of future cardiovascular disease,\" the researchers concluded.
While the Trial of Hypertension Prevention interventions were fairly intense-- individual and weekly group counseling sessions for the first three months and less frequently thereafter--to achieve a 25% to 35% reduction in dietary salt, even greater reductions are now being recommended.
The American Heart Association recommends a daily salt intake below 2,300 mg for most people, and the American Public Health Association has called for a 50% reduction in sodium in processed and restaurant foods.
Many patients would require help from a dietitian to achieve these goals, but an even greater effect than seen in the trial could be expected, Dr. Cutler said.
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