Taking a moderate amount of salt may be healthier than too little or too much, researchers reported in a study likely to fuel the debate over the health effects of salt in the diet.

Doctors for years have warned that high salt intake increases the risk of high blood pressure and other heart problems, but recent studies have begun to debunk that notion.

Although lowering salt intake is known to reduce blood pressure, research has yet to show whether that translates into better overall heart health in the wider population. A large review of studies released earlier this month suggested cutting salt may not improve the health of the general population.

In the latest entry in the debate, researchers at McMaster University in Canada found people who consumed a moderate amount of salt had the lowest risk of heart problems, while people who had high-salt diets had an increased risk of stroke, heart attack and other cardiovascular events.

Those in the study with low-salt diets had a higher risk of death from heart disease and an increased risk of being hospitalised for heart failure, the team reported in the Journal of the American Medical Association.

"Our findings highlight the importance of reducing salt intake in those consuming high-salt diets and the need for reducing sodium content in manufactured foods that are high in salt," Dr Salim Yusuf of McMaster, who helped lead the study, said in a statement.

"However, for those with moderate (or average) intake, whether further reduction of salt in the diet will be beneficial is an open question," he said.

The best way to settle that would be large clinical trials, the researchers said.

For the study, the team studied sodium and potassium levels found in a morning sample of urine taken from nearly 30,000 people in two clinical trials.

After about four years, some 16 percent of study participants had some kind of heart event. The team then looked for a correlation between salt intake and the risk of heart trouble.

As with prior studies, high salt intake - consuming 7 to 8 grams of sodium a day - was harmful to heart health. But low salt intake - consuming less than 3 grams of sodium a day - also carried risks of increased death from heart-related causes and hospitalization for heart failure.

The researchers said the findings could challenge US dietary guidelines, which recommend Americans consume less than 2.3 grams of sodium daily, or 1.5 grams for people who are more at risk of high blood pressure or heart disease.

A teaspoon of salt, or roughly 5 grams, holds around 2.3 grams of sodium.

In a commentary in the same journal, Dr Paul Whelton of Tulane University in New Orleans says the study results should be read with caution, noting problems with the way the researchers estimated salt intake based on a single morning sample of urine.

Whelton said the increased heart events in the study might be related to underlying disease. He also noted that there were far fewer heart problems at the low end of salt consumption compared with the high-intake group.

Taken together, he said, the scientific argument for reducing the amount of salt in processed foods remains strong and that the "available evidence does not support deviating from the stated goal of reducing the exposure to dietary sodium in the general population."    

High blood pressure, or hypertension, is one of the leading causes of strokes, heart attacks and other cardiovascular diseases, which together are the biggest killers worldwide and claim more than 17 million lives a year.   - Reuters