At the Tipping Point: Accomplishing Population‐Wide Sodium Reduction in the United States

Abstract

A convergence of recent policy recommendations and scientific advances has set the stage for renewed, aggressive, and hopefully effective efforts to reduce dietary sodium intake in the general population. The objective of this paper is to summarize the scientific rationale for population-wide sodium reduction, review recent scientific and policy developments, and offer guidance to health care providers. On average, as dietary salt (sodium chloride) intake increases, so does blood pressure (BP). Evidence includes results from animal studies, epidemiologic studies, migration studies, randomized trials (including several dose-response studies), and meta-analyses of clinical trials. To date, more than 50 randomized trials have been conducted. In a recent meta-analyses,1 a median reduction in urinary sodium of approximately 1.8 g/d (78 mmol/d) lowered systolic/diastolic BP by 2.0/1.0 mm Hg in nonhypertensive and by 5.0/2.7 mm Hg in hypertensive individuals. A few caveats are noteworthy. First, the BP response to sodium reduction, while direct and progressive, is nonlinear. Specifically, in dose-response studies, the slope of BP by sodium intake is steepest at sodium levels <100 mmol/d.2,3 Second, the BP response to changes in dietary sodium intake is heterogeneous,4 as is the BP response to other lifestyle interventions. The terms salt-sensitive and salt-resistant have been used to classify individuals in research studies; however the change in BP in response to a change in salt intake has a continuous, rather than binary, distribution.5 In general, the BP effects of sodium reduction tend to be greater in blacks, middle- and older-aged persons, and individuals with hypertension, diabetes, or chronic kidney disease. These groups tend to have a less responsive renin-angiotensin-aldosterone system.6 Dietary factors also influence the response to sodium reduction. For example, the Dietary Approaches to Stop Hypertension (DASH) diet3 and a high potassium intake7,8 blunt the rise in BP for a given increase in sodium intake. In addition to lowering BP, clinical trials have documented that a reduced sodium intake can prevent hypertension,9 lower BP in the setting of antihypertensive medication.10,11 and facilitate hypertension control.12,13. In observational studies, reduced sodium intake is associated with a blunted age-related rise in systolic BP,14 a reduced risk of atherosclerotic cardiovascular events,15,16 and a reduced risk of developing congestive heart failure.17 Accomplishing sodium reduction is similar to achieving other lifestyle modifications: a major public health approach is required in addition to changes in individual behavior. The need for a public health approach is even greater with sodium reduction than with other lifestyle modifications. In contrast to cigarette smoking, where usage is evident to the consumer, the sodium content of our diets is not readily apparent. Furthermore, more than 75% of consumed salt comes from processed foods.18 Hence, any meaningful strategy to reduce salt intake must involve the efforts of food manufacturers and restaurants. The need for public health approaches is also apparent in view of the global burden of hypertension (estimated worldwide prevalence of 972 million persons in 2000)19 and the limited success of individual-based sodium reduction interventions. Such interventions have been notoriously difficult to implement, especially in the setting of the current food supply, which is replete with "hidden" salt. In clinical trials, intensive interventions that focused just on salt reduction were able to shift mean intake to approximately 100 mmol/d (left panel of Figure 1).9,13,20 When efforts to reduce sodium intake were combined with weight loss9 or were part of a comprehensive lifestyle intervention program,21 sodium reduction was more modest (right panel of Figure 1), likely because of the complexity of making multiple lifestyle changes and potential tradeoffs when there are multiple lifestyle goals. Mean pre- and post-levels of urinary sodium excretion (a proxy of sodium intake) in 3 trials that tested interventions that focused only on salt reduction (left panel).9,13,20 Mean pre- and post-levels of urinary sodium excretion in 2 trials that combined sodium (Na) reduction with other lifestyle interventions (right panel). Trials of Hypertension Prevention, Phase 2 (TOHP2) tested an intervention combining sodium reduction with weight loss.9 PREMIER tested a comprehensive intervention combining sodium reduction with weight loss, increased physical activity, and adoption of the Dietary Approaches to Stop Hypertension (DASH) diet.21 TOHP1 indicates Trials of Hypertension Prevention, Phase 1; TONE, Trials of Nonpharmacologic Interventions in the Elderly. The scientific rationale for sodium reduction has been strong, and several recent advances have strengthened the case for population-wide sodium reduction. To date, policy recommendations have relied on evidence that