The Urgent Need to Reduce Sodium Consumption

Approximately 16.7 million individuals worldwide,¹ including 850 000 in the United States,² annually die of cardiovascular diseases. Almost 8 million of these deaths are attributed to hypertension (systolic blood pressure [SBP] ≥140 mm Hg and/or diastolic blood pressure [DBP] ≥90 mm Hg or taking antihypertensive medication).³ Many additional deaths are attributable to prehypertension (SBP ≥120-139 mm Hg and/or DBP ≥80-89 mm Hg). In the United States, more than 27% of adults have hypertension and another 31% have prehypertension.⁴ The lifetime probability of developing hypertension in the United States approaches 90%.⁵ Worldwide, more than 26% of adults have hypertension.⁶

Across populations, the progressive increase in blood pressure levels and the prevalence of hypertension with age are directly related to sodium intake. Numerous observational studies and randomized controlled trials document that high sodium intake increases blood pressure.⁷ The evidence implicating excess sodium intake as a major cause of high blood pressure levels has been called “overwhelming.”^{8 - 9}

Most of the world's population consumes 2300 to 4600 mg of sodium (100-200 mmol or 1-2 tsp of salt) daily. Average adult sodium intake in the United States approximates 4000 mg/d per 2000 kcal.¹⁰ Secular trends show a 55% increase in sodium intake from the early 1970s to 2000⁸ ; simultaneously, the age-adjusted prevalence of hypertension has increased by 50%.⁸

In the US diet, 77% of sodium comes from processed and restaurant foods, 12% occurs naturally in foods, 6% is added at the table, and 5% is added during cooking.¹¹ Many processed foods contain 1000 mg or more per serving, while typical restaurant meals contain 2300 to 4600 mg of sodium (Table). A consensus has emerged that sodium levels in processed and restaurant foods should be reduced substantially. Relevant policy developments in the United States and elsewhere, as well as possible solutions to address this important problem, are presented herein.

A sodium intake of less than 2400 mg/d has been a cornerstone of the National Heart, Lung, and Blood Institute's National High Blood Pressure Education Program (NHBPEP) recommendations to prevent and manage hypertension since 1993.¹² In 1998, the American Heart Association adopted a similar recommendation.¹³ In 2002, the US Department of Health and Human Services established an objective for 2010 that at least 65% of the population should consume less than 2400 mg/d of sodium.¹⁴ Currently, about 20% of the population meets that objective. No specific plan to achieve this objective has been implemented.

In 2003, the American Public Health Association adopted a resolution calling for a 50% reduction in sodium in processed and restaurant foods over 10 years. This resolution was subsequently endorsed by the NHBPEP Coordinating Committee, which is composed of representatives from 45 professional, voluntary, and federal organizations. In 2005, the National Academy of Sciences established adequate intakes for sodium: 1500 mg/d for 9- to 50-year-olds, 1300 mg/d for those aged 51 to 70 years, and 1200 mg/d for those aged 71 years or older.¹⁵ The tolerable upper intake was set at 2300 mg/d for these ages.

In June 2006, the Council on Science and Public Health of the American Medical Association (AMA) issued a report detailing the harmful effects of excess sodium consumption.⁷ This report recommended a minimum 50% reduction of sodium in processed and restaurant foods over 10 years, new labeling initiatives to warn consumers about high-sodium foods, and a public education campaign.

Given the designation by the US Food and Drug Administration (FDA) of salt as an ingredient that is “generally recognized as safe” (GRAS), the food industry is not limited in the amounts of salt it can add to processed foods. Because of the hazards of excess sodium intake, the AMA report recommended that the FDA revoke salt's GRAS status, an action sought on 2 occasions by the Center for Science in the Public Interest during the last 25 years.¹⁶ Revocation of GRAS status would require industry to petition the FDA to approve the use of salt as a food additive at specified levels in different types of food and the FDA to establish procedures for regulating these amounts. Revocation of GRAS status and other initiatives designed to reduce consumption of salt have not been FDA priorities.

Finland, the United Kingdom, Ireland, Australia, and New Zealand are ahead of the United States in addressing dietary sodium intake. Since the late 1970s, the Finnish Ministry of Social Affairs and Health has worked closely with food companies to decrease the salt content of products and has educated physicians and the public about the importance of lowering sodium intake. Foods high in sodium carry a high-salt label. Sodium intake has decreased by 40% during this period. Print and broadcast media played a major role in this reduction.⁸

Several years ago, the British government's Food Standards Agency divided processed foods into about 70 categories (eg, breads, canned vegetables, dry breakfast cereals, soups, doughnuts, and processed meats), calculated the percentage of dietary sodium derived from each, and set voluntary reduction targets, with the goal of reducing sodium consumption by 33% over 5 years.¹⁷ The Food Standards Agency is encouraging the food industry to make changes quickly and has indicated that it will take regulatory action if necessary. That agency has established a front-of-product, “traffic-light” labeling system that identifies products as high (red light), medium (yellow), or low (green) in sodium.

In Ireland, the Food Safety Authority developed a national program to reduce mean sodium consumption in adults to 2400 mg/d and is working to convince food manufacturers and preparers to reduce the sodium content of processed and prepared foods.¹⁸ The New Zealand and Australia National Heart Foundations have worked with food manufacturers to reformulate products and have created a program logo that identifies foods that have met strict standards for sodium (<400 mg per 100 g); the program has led to significant reductions in sodium in breads, breakfast cereals, and margarine.¹⁹

In 2007, the World Health Organization (WHO) issued a report declaring evidence “conclusive” that excess sodium causes hypertension. Consistent with WHO's previous recommendation in 2003 that adults consume less than 2000 mg/d of sodium, the 2007 report called for worldwide reformulation of processed and prepared foods to achieve the lowest possible sodium content, combined with consumer education and creation of an environment facilitating choice of low-sodium foods.²⁰

The time has come for the United States to implement this cohesive body of recommendations on sodium reduction to achieve the public health benefits that would accrue from even small reductions in the population blood pressure distribution. It is estimated that a 50% reduction in sodium intake would lower mean SBP at least 5 mm Hg, resulting in a 20% lower prevalence of hypertension and a reduction in mortality rates of 9% for coronary heart disease, 14% for stroke, and 7% for death from all causes.²¹ One estimate suggests that these changes could prevent at least 150 000 deaths annually in the United States.²²

The impact of sodium reduction could well be even greater considering several recent studies. Long-term follow-up of 2 randomized trials in which intervention participants lowered sodium intake by 33% demonstrated a 25% reduction in cardiovascular disease events (P = .04).²³ In Finland, the 40% reduction in sodium intake over 30 years was accompanied by a 10-mm Hg decrease in mean blood pressure and an 80% reduction in mortality due to stroke.⁹ Extrapolating from published calculations for Canada, a 50% reduction in sodium could also save billions of dollars in health care costs.²⁴

Although physicians can and should educate patients about reducing sodium intake, even highly motivated individuals will find it difficult because 80% of sodium intake is derived from salt added by food processors and restaurants. Thus, any meaningful strategy to reduce population sodium intake depends heavily on food processors and restaurants reducing the amount of sodium added to food. A reasonable interim target is a 50% reduction in sodium in processed foods, fast foods, and restaurant meals over the next decade. The Healthy People 2010 objective on sodium cannot be met without such action.

One approach would be for food processors and restaurants to progressively lower sodium over several years. Gradual, steady reductions might be better accepted by consumers than a sudden large change. Another approach would be to divide processed foods into categories, as is done in the United Kingdom, and set limits for each category. Either way, the food processing and restaurant industries can reformulate products by using other spices for flavoring.

In the absence of substantial voluntary reductions in sodium, a regulatory approach is necessary. Warning labels for foods high in sodium would assist consumers in understanding the negative health effects of processed and prepared foods. Changes in food labeling regulations could require companies to put recognizable symbols or colors on the labels of products that are high in sodium.

Ultimately, substantial cooperation among the government, the food industry, clinicians, and the public will be required to accomplish meaningful change and enable a larger proportion of the population to experience the benefits of reduced dietary sodium. With an appropriate food industry response, counseling of patients, public education, and knowledgeable use of food labels, sodium intake could be reduced without inconvenience or loss of food enjoyment.

In the Dietary Approaches to Stop Hypertension-Sodium Trial, the largest decrease in SBP occurred when sodium intake was reduced from 2300 to 1500 mg/d.²⁵ Attaining this level would necessitate reducing sodium in processed and restaurant foods by approximately 80% based on current dietary habits. From a public health perspective, lowering sodium by that amount should be the long-term goal.

Clinicians can help make sodium reduction in the nation's food supply a reality by lending their voices to the calls for action on this important issue. Unless the health care community consistently makes this a highly visible issue, the solutions outlined above will continue to be elusive and the health of the public will continue to be compromised.