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Lower Levels of Sodium Intake and Reduced Cardiovascular Risk
Study Questions:
Is a low or very low salt diet a good recommendation for prevention of cardiovascular disease (CVD)?
Methods:
Phases I and II of the TOHP (Trials of Hypertension Prevention) were designed to evaluate supplement and lifestyle interventions on blood pressure in men and women ages 30-54 years with high normal blood pressure. Multiple 24-hour urine specimens were obtained over 18 months, which provided an estimate of sodium intake. The primary endpoint for the 10- to 15-year TOHP follow-up study was CVD or CVD death, including myocardial infarction (MI), stroke, coronary artery bypass grafting, percutaneous transluminal coronary angioplasty, or death from CVD.
Results:
During post-trial surveillance, 193 CV events or CVD deaths occurred among 2,275 participants not in a sodium reduction intervention. Median sodium excretion was 3630 mg/24 hours, with 1.4% of the participants having excretion <1500 mg/24 hours and 10% <2300 mg/24 hours, consistent with national levels. Compared to those with sodium excretion of 3600 to <4800 mg/24 hours, risk for those with sodium <2300 mg/24 hours was 32% lower after multivariable adjustment (hazard ratio, 0.68; 95% confidence interval, 0.34-1.37; p for trend = 0.13). There was a linear 17% increase in risk per 1000 mg/24 hours (p = 0.05). Spline curves supported a linear association of sodium with cardiovascular events, continuing to descend from 3600 to 2300 and 1500 mg/24 hours, although the data were sparse at the lowest levels. Controlling for creatinine levels had little effect on these results.
Conclusions:
Results from the TOHP studies, which overcome the major methodological challenges of prior studies, are consistent with overall health benefits of reducing sodium intake to the 1500 to 2300 mg/day range in the majority of the population, in agreement with current dietary guidelines.
Perspective:
The Institute of Medicine (IOM) recently concluded that while salt restriction is necessary, there is no evidence of safety and efficacy for supporting a target of <2000 mg sodium daily. The safety concern was based on some evidence of a J-shaped curve of sodium intake and CVD. The IOM conclusion is in conflict with the recommended daily sodium intake to reduce hypertension and CVD that varies with the American Heart Association guideline of <1500 mg, the World Health Organization of <2000 mg, and Dietary Guidelines for Americans of <2300 mg with further reduction to <1500 mg for persons >51 years, African Americans, and those with hypertension, diabetes, and chronic kidney disease. The <1500 mg applies to approximately 50% of Americans including children and the majority of adults. There is little more important and more controversial health issue than dietary guidelines for consumers and stakeholders, for which the evidence-based methodology to review the science is so difficult and the bias is so great.
Keywords: Myocardial Infarction, Stroke, Life Style, Nutrition Policy, Blood Pressure, Risk Factors, Sodium Chloride, Dietary, Diet, Sodium-Restricted, Cardiovascular Diseases, Coronary Artery Bypass, Hypertension, Diabetes Mellitus, Renal Insufficiency, Chronic
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