Balancing salt consumption may be optimal for health

August 18, 2014

Two studies published in the New England Journal of Medicine assessed sodium and potassium intake and related them to blood pressure as well as to deaths, heart disease, and strokes.

The Prospective Urban & Rural Epidemiological (PURE) study, led by investigators from the Population Health Research Institute, McMaster University, and Hamilton Health Sciences, followed more than 100,000 people for nearly four years. The data for the studies was based on a single, fasting, morning urine specimen from 102,216 adults from 18 countries.

Current intake of sodium in the United States is approximately 3.4 g per day, according to the U.S. Centers for Disease Control and Prevention. Researchers have shown that the effects of increasing sodium intake on raising blood pressure—a risk factor for heart attack, heart failure, stroke, and other problems—become dramatically worse as intake rises above 5 g per day, especially among people who already have high blood pressure, or who are older than 55, or both. However, the blood-pressure effects are more modest at average levels of sodium consumption (3–5 g per day) and not evident at low levels of intake below 3 g of sodium per day.

“While there has been much focus on reducing salt in the diet, an important and ignored approach to lowering blood pressure is increasing the amount of potassium consumed. A balanced approach is what is likely to have the greatest benefit in lowering blood pressure,” said Andrew Mente, the lead author of one report, and Assistant Professor of Clinical Epidemiology and Biostatistics at McMaster University. “This can be achieved by moderation in salt intake, combined with eating lots of fruits and vegetables.”

While too much salt has long been recognized as a serious health risk, the researchers have also found that there may be a risk from eating too little. In fact, the lead author of the second report, Martin O’Donnell, suggests that what is now generally recommended as a healthy daily ceiling for salt consumption appears to be set too low.

“Low sodium intake does reduce blood pressure modestly, compared to moderate (or average) intake, but low sodium intake also has other effects, including adverse elevations of certain hormones that are associated with an increase in risk of death and cardiovascular diseases. The key question is whether these competing physiologic effects result in net clinical benefit or not,” said O’Donnell, an associate clinical professor at McMaster University and National University of Ireland Galway.

“In the PURE study, we found the lowest risk of death and cardiovascular events in those who consumed moderate amounts of sodium intake (3–6 g per day), with an increased risk above and below that range. While this finding has been reported in previous smaller studies, PURE is the largest international study to study sodium intake and health outcomes, and adds considerable strength to the contention that moderate sodium intake is optimal,” said O’Donnell.

Taken together, the papers show there is a “sweet spot” for sodium consumption, where too much or too little can be damaging, while a moderate amount between 3–6 g is optimal.

Blood pressure and sodium study

Mortality and sodium study