People whose diets contain moderate levels of sodium may have healthier hearts and live longer than those who consume too much or too little of the mineral, new research suggests.

In a large international study, researchers found that men and women who ate between 3,000 and 6,000 milligrams of sodium per day had a lower risk of major cardiovascular problems, such as heart attack, stroke or heart failure, and they also had a lower risk of dying over a four-year period compared with people who consumed more, or less, sodium.

After following participants for nearly four years, the analysis found that people who consumed more than 6,000 mg of sodium daily, as well as those who consumed less than 3,000 mg daily, had a higher risk of dying from any cause, and from heart-related causes during the study, and were more likely to have heart problems.

"Our study looked at optimal levels of sodium around the world, and we found that being in the middle is the safest amount for optimal health," said study author Andrew Mente, an associate professor of clinical epidemiology and biostatistics at McMaster University in Ontario, Canada.

On average, U.S. adults consume 3,400 mg of sodium daily.

However, current federal dietary guidelines encourage Americans to reduce sodium intake: They recommend that most people ages 14 to 50 limit their sodium intake to 2,300 mg daily, and advise people ages 51 and older, as well as groups at high risk of heart disease (including African Americans, and adults with high blood pressure, diabetes or kidney disease) to cut back to 1,500 mg daily. [13 Easy Kitchen Fixes that Can Help You Lose Weight]

"The findings indicate that current sodium guidelines need to be rethought," Mente said.  The study was important because it was large, and looked at the long-term effects of sodium on actual clinical events, he said.

The results also showed that very few people — only 4 percent — had sodium intakes that fell within the U.S. guidelines.

Rethinking sodium

For the study, the researchers evaluated nearly 102,000 people ages 35 to 70 in 17 countries, ranging from wealthy nations to low-income countries. Most participants had no history of heart disease, so the sample represented the general population rather people at high-risk of heart disease, the researchers said in their report, published online on Aug. 13 in The New England Journal of Medicine.

Each participant provided one sample of morning urine, which the researchers used to estimate their 24-hour sodium and potassium excretion levels, which are considered a reliable measure of dietary intake for these two nutrients.

Although having too much salt in the diet receives more attention, there's evidence to suggest there may also be health consequences from getting too little of it.

Other recent studies have also found a link between diets low in sodium and an increased risk of death and heart problems. Further research is needed to explain why an increased health risk is seen when sodium levels fall, Mente said.

The data also showed that people whose diets contained more than 1,500 milligrams of potassium per day were less likely to die during the study or have heart disease compared with those getting less potassium.

Potassium minimizes the impact of sodium on blood pressure, Mente said, but he suspects that higher potassium intakes could also be a marker of a generally healthier diet, because fruits and vegetables are rich in potassium.

As for the practical implications of the research, Mente said that if people are eating large amounts sodium (more than 6,000 mg of sodium daily) or have high blood pressure, it still makes sense to limit salt by using less in cooking and at meals, as well as to cut back on processed foods, such as cured meats, canned soups and sauces.

But people who consume sodium in moderation (between 3,000 and 6,000 mg) might not need to lower their intake, and doing so may even increase heart disease risk, Mente said.

A large clinical trial is needed to compare the health effects of a group on a low-sodium diet to people following their usual diets.

In the meantime, "For a healthier heart and to live longer, rather than focusing on a single nutrient, such as restricting sodium intake, it's more important to follow a healthy diet, get regular exercise and not smoke," Mente said.

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