Studies show a balanced approach to sodium and potassium intake is likely to have the greatest health benefits.

HAMILTON, Ontario – Two studies published Aug. 14 in the New England Journal of Medicine address sodium and potassium intake and relate them to blood pressure as well as to deaths, heart disease and stroke. The bottom line — too much is bad, there are issues with consuming too little, and a balanced approach is recommended.

The Prospective Urban and Rural Epidemiological (PURE) study, which is led by investigators from the Population Health Research Institute, McMaster Univ. 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 US is approximately 3.4 grams per day, according to the Centers for Disease Control and Prevention (CDC), and some guidelines have recommended that the entire population lower its sodium intake to below 2.3 grams per day. Researchers have shown that the effects of increasing sodium intake on raising blood pressure become worse as intake rises above 5 grams per day, especially among people who already have high blood pressure or who are older than 55.

But the blood pressure effects are more modest at average levels of sodium consumption (3 to 5 grams per day) and not evident at low levels of intake below 3 grams of sodium per day, said Andrew Mente, the lead author of one report, and an assistant professor of clinical epidemiology and biostatistics at McMaster Univ.

“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,” Mente said. “A balanced approach is what is likely to have the greatest benefit in lowering blood pressure. This can be achieved by moderation in salt intake, combined with eating lots of fruits and vegetables.”

While too much salt has been recognized as a health risk, the researchers also found there may be a risk from eating too little. The lead author of the second study, Martin O’Donnell, an associate clinical professor at McMaster Univ., said that what is now generally recommended as a healthy daily ceiling for salt consumption may be set too low.

“Low sodium intake does reduce blood pressure modestly, compared to moderate 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,” he said. “The key question is whether these competing physiologic effects result in net clinical benefit or not.

“In the PURE study, we found the lowest risk of death and cardiovascular events in those who consumed moderate amounts of sodium intake (3 to 6 grams 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.”

In an accompanying editorial in the journal, Professor Suzanne Oparil of the Univ. of Birmingham, Ala. urged reconsideration of current guidelines and recommended randomized trials comparing outcomes in people who consume usual salt intake to very low intake to assess if further reductions in sodium reduces clinical events.

“These provocative findings beg for a randomized, controlled outcome trial to compare reduced sodium intake with usual diet,” Prof. Oparil wrote. “In the absence of such a trial, the results argue against reduction of dietary sodium as an isolated public health recommendation.”

The studies may be viewed by visiting the New England Journal of Medicine web site.