Salt: friend or foe?

Dietary guidelines advise against the consumption of too much salt.
A high intake of sodium causes raised blood pressure—an established risk factor for heart disease, stroke, and kidney disease.
But how much salt is too much? And could a very low salt intake also be detrimental?

The effects of salt consumption on health are controversial, but reduced salt intake is mostly believed to decrease the risk of cardiovascular disease.

The 2010 Dietary Guidelines for Americans recommend a maximum daily consumption of 2300 mg salt for healthy adults and 1500 mg for people at raised risk of heart disease (eg, those older than 51 years, people with diabetes, and black people).

The American Heart Association even advises that everyone adheres to the 1500 mg limit, irrespective of age or race. However, most people still eat too much salt—on average, US adults consume 3400 mg (about 1·5 teaspoons) daily.

In May, 2013, the Institute of Medicine reviewed recent evidence (39 studies) and reported that a very low salt intake might not be as beneficial as was previously thought, at least for those at increased risk of heart disease.

Less than 2300 mg salt daily could even increase some cardiovascular risk factors, such as blood lipids and insulin resistance, potentially triggering heart problems. Moreover, no evidence suggested a benefit of an ultra-low sodium intake (<1500 mg daily) in any population.

High study heterogeneity, and the fact that the effects of reduced sodium intake on health outcomes cannot always be distinguished from those of overall diet changes, make accurate conclusions difficult.

The report concludes that more trials are needed to address gaps in the data, especially studies of the effects of a 1500—2300 mg daily salt intake in different groups.

The report needs cautious interpretation—it does not suggest that people use salt freely.

The Institute agrees that a link between high salt consumption and increased risk of cardiovascular disease persists, and that average intake needs to be reduced.

However, the findings about very low sodium levels will help to clarify public health messages (eg, updated US dietary guidelines, due in 2015) and hopefully improve health outcomes.

G Mohan.