We are used to being told that eating too much salt is bad for our health. However, a major new international study has found that not eating enough salt can also be harmful.

The study, the largest of its kind ever undertaken, involved hundreds of scientists from 18 countries, including Prof Martin O'Donnell of NUI Galway. It followed the progress of over 100,000 people for almost four years.

People typically consume between 3.5 and four grams of salt per day, with some guidelines recommending that this should be lowered to less than 2.3g per day. However, the study found that consuming less than 3g per day may be harmful to health.

"In the study, we found the lowest risk of death and cardiovascular events in those who consumed moderate amounts of sodium intake (three to six grams per day), with an increased risk above and below that range.

While this finding has been reported in previous smaller studies, this is the largest international study to look at sodium intake and health outcomes, and adds considerable strength to the contention that moderate sodium intake is optimal," Prof O'Donnell commented.

However, he emphasised that these findings should not lead to complacency when it comes to salt consumption, as high salt intake is still a health risk, particularly in those with high blood pressure.

"People should avoid adding salt to their foods, as many foods already contain salt, and should reduce or avoid processed foods that contain high salt. Moderate salt intake is only one part of a healthy diet. Other aspects of a balanced diet are important, such as increasing fruit and vegetable intake," he insisted.

High blood pressure is a risk factor for heart problems, including heart attacks and stroke. The scientists were able to show that the effects of increasing salt consumption on raising blood pressure became more apparent when more than five grams of salt were consumed per day. This was particularly true among people aged 55 and older, people who already had high blood pressure, or both.

However these effects on blood pressure are ‘more modest' at average levels of salt consumption - three to five grams per day - and are not evident if less than three grams of salt is consumed per day.

But Prof O'Donnell pointed out that while low salt intake can potentially lower blood pressure, it can also have other effects, ‘including elevations of certain hormones that are associated with an increase in risk of death and cardiovascular diseases'.

The findings of the study were published in two reports and they concluded that both too little and too much salt can be harmful to health. The general population should therefore aim for an ‘optimal range' of three to six grams per day, the scientists said.

Details of these findings are published in the New England Journal of Medicine.

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