Reducing Sodium in American Diet Would Save Hundreds of Thousands of Lives

Hundreds of thousands of lives could be saved over 10 years if Americans reduced their sodium consumption to the levels recommended in federal guidelines, according to a new study by researchers at UC San Francisco (UCSF), Harvard Medical School and Simon Fraser University in Canada.

Described this week in the journal Hypertension, the study emerged from a workshop convened last year by the U.S. Centers for Disease Control and Prevention (CDC), which sought to quantify the health benefits of population-wide sodium reduction.

The CDC brought together groups of scientists from the three universities, who each used completely different computer models to estimate how lowering sodium would save lives – largely by reducing the number of heart attacks and strokes. All three models found consistent, substantial benefits of reducing U.S. sodium consumption from the current level of intake to a level close to the upper limit of the federal guideline of 2,300 mg/day in the following ways:

• Immediately reducing sodium intake to the current upper limit of the guidelines would save 500,000 to 850,000 lives over the next 10 years.
• Gradually reducing sodium intake through processed or restaurant-prepared foods by 4 percent per year over 10 years would still yield substantial health benefits, saving 280,000 to 500,000 lives over a decade.

“No matter how we look at it, the story is the same – there will be huge benefits in reducing sodium,” said Pam Coxson, PhD, a UCSF mathematician and the lead author on the paper who performed one of the three analyses. Coxson is based at the UCSF Center for Vulnerable Populations, located at the San Francisco General Hospital and Trauma Center (SFGH).

The overall average sodium consumption in the United States has been estimated at 3,500 mg/day, well above the upper limit of 2,300 mg recommended by federal agencies and the Institute of Medicine. The average American male consumes even more – about twice as much sodium as recommended.

Strange Sources of Salt in the American Diet

Sodium in the diet is essential for the normal function of our cells in tissues throughout the body. However, high excess sodium in the diet contributes to high blood pressure and cardiovascular disease, the No. 1 killer in the United States, accounting for more than 800,000 deaths a year and costing $273 billion in health care dollars in 2010 alone, according to the CDC.

About 45 percent of these cardiovascular deaths are attributable to high blood pressure, and numerous medical studies have already demonstrated how reducing dietary salt – the primary source of sodium – can lower blood pressure and reduce the risk of a heart attack or stroke.  

However, individuals find it difficult to reduce sodium in their diet because most is already added to the processed, packaged or prepared food that they consume.

People may think that forgoing salt at the dinner table would adequately reduce their sodium consumption, Coxson said, but in truth most of the sodium we consume enters the food supply long before it reaches the table. Some 80 percent of the sodium we consume comes from processed foods – and not necessarily the ones you would expect.

According to the CDC, bread is the No. 1 source of sodium in the diet, and together with other cereals contributes about one-third of our daily sodium intake. Canned soup can be so high in sodium that a single can may constitute a significant amount of our daily recommended allowance. Processed meats like turkey are often high in sodium, and even fresh meat like chicken may be injected with salt solutions before reaching market. As much as one-third of the sodium in the U.S. diet comes from restaurant meals and other food prepared outside the home.

Salt is added to food for a variety of reasons, said Kirsten Bibbins-Domingo, MD, PhD, senior author on the study, an associate professor in residence at UCSF and director of the UCSF Center for Vulnerable Populations. It is an inexpensive way to boost the flavor of processed foods, and in some cases acts as a preservative, giving it a longer shelf life. Salt is also added to fresh meat for water retention, adding to its weight.

How Lowering Sodium Would Save Lives

A 2010 Institute of Medicine report recommended population-wide approaches to sodium reductions to gradually reduce sodium in the food supply through regulation, surveillance, education and voluntary action.

What has been important for policymakers is determining the magnitude of benefit of these public health efforts, Bibbins-Domingo said.

Last year’s CDC workshop sought to quantify the health benefits of population-wide sodium reduction using three separate models. The first took into account the results of the Framingham Heart Study, a longitudinal study that began decades ago and looks at diet, exercise, drugs and other factors on cardiovascular health.

The second model pooled data from the results of multiple clinical trials that involved hypertension-lowering drugs. The third used outcomes from long-term trials of hypertension prevention that specifically tested the cardiovascular effects of salt reduction in thousands of adults who were followed for four years.

While the new study analyzed the benefit of sodium reduction, it did not consider how that reduction would be achieved – whether through voluntary reductions or through new federal regulations.

Some countries, including England, Finland and Argentina, regulate salt, but under current federal law, salt is an unregulated food ingredient because it is generally regarded as safe by the U.S. Food and Drug Administration (FDA). The Institute of Medicine recommended that the FDA move salt out of this category in 2010.

This is really about consumer choice, Bibbins-Domingo said. Putting less salt in processed foods allows consumers to add their own should they choose to do so. Some studies suggest that when salt is kept out of prepared foods and people are allowed to add their own, they eat less overall, she added.

The article, “Mortality Benefits From US Population-Wide Reduction In Sodium Consumption – Projections From Three Modeling Approaches” is authored by Pamela G. Coxson, Nancy R. Cook, Michel Joffres, Yuling Hong, Diane Orenstein, Steven M. Schmidt and Kirsten Bibbins-Domingo. It was published online in the journal Hypertension on Feb. 11.

In addition to UCSF, authors on the study are affiliated with Harvard Medical School in Boston; Simon Fraser University in Burnaby, Canada; the U.S. Centers for Disease Control and Prevention in Atlanta, GA; and Lund University in Sweden.

This work was funded by the CDC, with additional support provided by the American Heart Association, Western States Affiliates.