Let’s say you wake up tomorrow morning and have two pancakes drizzled with butter and syrup. For lunch, you decide on a cup of canned vegetable soup. Around 3 p.m., you grab a snack of 10 pretzels. On your way home from work, you pick up a cup of pre-made macaroni and cheese. At the end of the day, you will have consumed a whopping 4,300 milligrams of salt, about double what is currently recommended by health experts.
Public health advocates typically express concern about such high salt consumption, but the medical reality is that the relationship between dietary sodium and health remains unclear — especially for the 6 million Americans living with heart failure.
Despite decades of discussion and dispute, scientists have failed to determine proper salt and nutrient requirements for patients with heart failure. Several recent studies have rekindled the debate, spotlighting a divided scientific community. Basic clinical research is still lacking, according to an editorial published earlier this month in a medical journal. In the meantime, millions of Americans remain as puzzled as ever about what to have for dinner and how much salt they should sprinkle on top.
“I can’t really tell you what you should be eating if you have heart failure,” says Dr. Michael Rothberg, an internist at Baystate Medical Center of Tufts University. “There aren’t any good studies on it.”
If you think of the heart as a pump, then you can think of heart failure as a weak or malfunctioning pump. The heart is unable to either fill up or eject blood to the rest of the body as well as it should, causing shortness of breath, weakness, and swelling of the legs and feet. There are a number of reasons that can happen. Coronary artery disease, high blood pressure and diabetes are the leading causes, according to the Centers for Disease Control and Prevention.
An estimated 20 percent of patients with heart failure will die within the first year of diagnosis, according to a 2009 report by the American Heart Association. The disease was associated with more than 280,000 deaths in 2006. The total cost of health care services, medications and lost productivity resulting from heart failure will be more than $39 billion this year alone, according to the association.
Increased retention of salt and water aggravates the signs and symptoms of heart failure. Consuming less dietary salt might also logically improve a patient’s disease, or so the traditional scientific reasoning goes.
So people living with heart failure should consume less than 2,000 milligrams (less than a teaspoon) of salt per day, as recommended by the American Heart Association and the Institute of Medicine.
“The average sodium consumption in this country is close to 4,000 milligrams per day,” says Clyde Yancy, M.D., national president of the American Heart Association and medical director of the Baylor Heart and Vascular Institute in Dallas. “That is so far above the threshold we need that in reality there needs to be an across-the-board reduction in sodium consumption in both patients with heart disease as well as in healthy individuals.”
The majority of the salt we consume comes from packaged foods or dining out at restaurants, according to a 1991 study on nutrition. Only about 10 percent comes from using the salt shaker while cooking at home or seasoning food at the table.
Although most physicians agree that 4,000 milligrams of salt per day is too much, several recent studies have suggested that severe salt restriction might actually be harmful to patients with heart failure, although the evidence is far from definitive.The American College of Cardiology and the American Heart Association jointly established that patients with heart failure should reduce their sodium intake. But the associations classify that guideline as level of evidence C, which means it is based on expert consensus alone. There are no definitive clinical studies testing the recommendation, which is instead based on “anecdotes and opinions,” according to Yancy in his 2008 review on the sodium controversy.
Last year, researchers in Italy found that heart failure patients on a normal sodium diet of about 2,800 milligrams per day combined with tightly restricted fluid intake and high-dose diuretics had less hospital readmissions and better kidney hormone function than those patients who were on low-sodium diets of about 1,800 milligrams per day.
“Though this is very provocative work, it is still not sufficiently compelling to change guidelines,” says Yancy. “These patients were put on extremely high doses of diuretics, which could have altered their sodium requirements. And they were restricted to 1,000 milliliters of fluid, which is very difficult to maintain, almost not practical.”
Rothberg, who wrote an editorial this month questioning the American Heart Association’s current dietary recommendations, also believes that the Italian study needs to be expanded and repeated before any patients should think about changing their current diet. But that research is urgently needed, he says.
“This issue is so important in heart failure specifically, as opposed to some other heart diseases, because patients with heart failure have notoriously bad outcomes,” says Rothberg. “This is an area of research where we can really make a difference in people’s lives.”
The role of dietary sodium is only a small part of the debate. A study published this month by researchers at the University of Massachusetts found that although patients with heart failure generally reduce their sodium consumption as compared with the general population, they also follow diets deficient in essential micronutrients like calcium, magnesium and potassium. To what extent that influences the course of disease is still unclear.
Experts argue that all of this uncertainty after years of scientific debate raises an important question: Why have there never been any large-scale, well-designed clinical trials on the sodium and nutrient requirements for the millions of Americans with heart failure?
“It’s a very difficult study design,” says Dr. Frank Sacks, a leading researcher on cardiovascular disease prevention in the department of nutrition at the Harvard School of Public Health. “These are very sick patients with complicated needs. It requires a team of experts who don’t often collaborate at one institution: You need a nutritionist, an expert on heart failure and an expert in conducting clinical trials.”
Sacks’ team, along with researchers at Johns Hopkins Medical Center, is in the preliminary stages of planning a large-scale clinical trial to assess dietary needs of patients with the disease. He hopes it will provide definitive answers to pressing questions about salt and other nutrients.
Another issue is that industry funding for this type of research is rare. Investigators rely heavily on government grants.
“I doubt the pharmaceutical industry would be interested in funding something like this,” says Sacks. “They’re interested in seeing their drugs tested, not in investigating dietary requirements.”
The National Heart, Lung and Blood Institute has issued national program announcements to fund research on nutrition and heart failure. The most recent announcement expired earlier this season, but has been approved for rerelease in several months.
“We’ve been encouraging people to apply for research on these topics,” says Abby Ershow, a program officer at the institute. “So far we’re only supporting a few small studies in humans.”