Salt reduction in the United States

In June 2006, the American Medical Association catapulted its salt policy into the headlines. In a bold step the association's membership voted to implement several strategies to reduce salt intake. The members voted (a) to urge the Food and Drug Administration (FDA) to revoke the “generally recognized as safe” (GRAS) status of salt and develop regulatory measures limiting the amount of salt in processed and restaurant foods; (b) to establish quantifiable milestones, specifically a 50% reduction over the next decade, in the salt content of processed foods, fastfood products, and restaurant meals; (c) to join in partnership with organisations to educate consumers about the benefits of long term salt reduction; and (d) to work with the FDA to improve food labelling and develop warning labels for foods high in salt. The association's decision to advocate salt reduction follows a recent series of reports in the United States recommending sharp reductions in salt consumption, largely because of its adverse effects on blood pressure.^1-5

The response from industry was swift and predictable. Leading the charge against the proposal is the Salt Institute, an international trade organisation of salt producers. In a news release, the Salt Institute claimed that “the American Medical Association has misread the science, confusing blood pressure effects with health outcomes.” The Salt Institute, now allied with the US Chamber of Commerce, argues that policy making should rely only on evidence from clinical trials that use clinical outcomes such as stroke and mortality rather than intermediary outcomes such as blood pressure. However, blood pressure is an important, aetiologically relevant risk factor for cardiovascular and renal diseases and is widely accepted as a valid marker for policy making.⁶ In addition, a large scale, long term, lifestyle modification trial with clinical outcomes is unrealistic. It would not be worth the considerable time and expense because of the overwhelming evidence for salt's adverse effects on blood pressure.⁷

Reducing salt intake is similar to achieving other lifestyle modifications in that a substantial public health approach will be required in addition to changes in individual behaviour. The need for a public health approach is even greater with salt reduction than other lifestyle modifications. In contrast to cigarette smoking, where use is evident to the consumer, the salt content of our diets is not readily apparent: over 75% of consumed salt comes from processed foods.⁸

Hence, any meaningful strategy to reduce salt intake must involve the efforts of food manufacturers and restaurants, either voluntarily (by persuasion) or involuntarily (by regulation). The latter may be required, given the initial response of commercial bodies to the American Medical Association's proposal. The need for public health approaches is also apparent, given the global burden of hypertension (estimated worldwide prevalence of 972 million persons in 2000⁹) and the limited success of lifestyle interventions designed to reduce individuals' salt intake. Such interventions have been notoriously difficult to implement, especially in the setting of a food supply containing “hidden” salt.

In clinical trials, intensive interventions that focused just on salt reduction have shifted mean intake to about 100 mmol (2.3 g) of sodium (equivalent to 5.8 g of salt) a day.^10-12 When efforts to reduce salt intake were combined with weight loss¹¹ or as part of a comprehensive lifestyle intervention programme,¹³ salt reduction was more modest, probably because of the complexity of making multiple lifestyle changes and potential tradeoffs when there are several lifestyle goals.

The proposal by the American Medical Association may represent a turning point in public health efforts that have so far been largely ineffective in the US. The actions of doctors and their leadership carry enormous weight, as they did for tobacco control efforts. It is reasonable to conceive that physicians' actions have been an integral, if not essential, component of tobacco control efforts in the US, given their influence on individual patients, their communities, and healthcare policy.

Advice to reduce salt intake has been issued for about 30 years, despite persistent and highly aggressive attempts by commercial interests to weaken recommendations. With publication of the US Dietary Guidelines report⁴ and a subsequent “harmonisation” process, salt recommendations are now uniform and accepted by all branches of the federal government. Recommendations are also more stringent—the currently recommended upper limit of sodium intake is 100 mmol a day in the general population and 65 mmol a day in people who are especially sensitive to the adverse effects of sodium (African-Americans, middle aged and older individuals, and people with hypertension, diabetes, or chronic kidney disease).⁴

The critical issue in the US, as in most other countries, is developing a comprehensive strategy to achieve meaningful, population-wide reduction in salt intake. In this setting, the association's proposal is a logical and coherent framework for accomplishing this vitally important public health objective.