Confusing research on salt and heart: Study

By Dr. Ananya Mandal, MDMay 4 2011

According to the latest European study, people who eat lots of salt are not more likely to get high blood pressure, and are less likely to die of heart disease than those with a low salt intake. This is contrary to what has been known till date. The U.S. guidelines recommend that Americans consume less than 2,300 milligrams of salt daily - 1,500 mg in certain people who are more at risk for high blood pressure or heart disease.

Study author Dr. Jan Staessen, of the University of Leuven in Belgium said that the findings “certainly do not support the current recommendation to lower salt intake in the general population.” Current salt guidelines, including those released by the U.S. government in January, are based on data from short-term studies of people who volunteered to be assigned to a low-salt or high-salt diet, Staessen said. He added that while earlier trials suggested a blood pressure benefit with lower salt intake, research has yet to show whether that translates into better overall heart health in the wider population.

To come to this conclusion the team used data from two different studies, incorporating a total of about 3,700 Europeans who had their salt consumption measured through urine samples at the start of the studies. Staessen and his colleagues broke the participants up into three groups: those with highest and lowest salt intakes, and those with average intake. None of the participants had heart disease at the outset, and two thirds had normal blood pressure. They were followed for an average of 8 years, during which researchers determined how many of them were diagnosed with heart disease, and in a smaller group, how many got high blood pressure. The findings are published in the Journal of the American Medical Association (JAMA).

The results revealed that the chance of getting heart and blood vessel diseases did not differ in the three groups. However, participants with the lowest salt intake had the highest rate of death from heart disease during the follow up (4 percent), and people who ate the most salt had the lowest (less than 1 percent). Across all three salt-intake groups, about one in four study participants who started out with normal blood pressure were diagnosed with high blood pressure during follow up. They also noted that systolic blood pressure increased as salt intake increased over time - but the change was very small, so it may not be important to health outcomes, Staessen said.

They concluded that reducing salt may still be a good idea for people who already have high blood pressure or who have had heart problems in the past, he added, but the study found no evidence that dietary salt causes those conditions to arise. “Lower sodium intake is recommended for people with high blood pressure and people with heart failure, but recommending it to the population as a whole, I wouldn't do without proving it's completely safe…If one lowers sodium intake to lower blood pressure, this change in sodium activates several systems (including the renin-angiotensin aldosterone system) that conserve sodium, and those systems are implicated in disease processes such as damaging the arterial wall and kidneys…It's clear that one should be very careful in advocating generalized reduction in sodium intake in the population at large,” Staessen said. “There might be some benefits, but there might also be some adverse effects.”

Dr. Hillel Cohen, an epidemiologist at the Albert Einstein College of Medicine in New York, added that when restaurants or food companies put less salt in their products, they may put in other potentially harmful products to make up for the lost taste, or as preservatives. Cohen warned that consumers shouldn't change their salt-eating behaviour based on the limited studies that have tried to determine the link between sodium and heart risks. Cohen was an independent observer. The authors caution that their analysis included only white Europeans, and so the results may not translate to people of other ethnicities.

Gina Lundberg, a preventive cardiologist in Atlanta, supports the 1,500-milligram guideline. “We're all eating too much sodium because we eat too many prepared, processed foods.”

Leaders in the salt industry applaud the new research. This study basically says that salt reduction to reduce cardiovascular disease is a strategy that is not going to work, says Morton Satin, vice president of science and research for the Salt Institute, an industry group.