Arguments over salt and health have broken out on both sides of the Atlantic, with dissenting opinions among individual experts and even professional societies. What’s going on?

New IOM report

The latest round of the salt controversy was triggered by the Institute of Medicine (IOM) in the United States, a very conservative and scientific organisation. Their latest report had two key messages, the first confirming the positive association between high sodium intakes, high blood pressure and the risk for heart disease. No drama there. The contentious finding was that there was not a strong scientific case for shifting from moderate to low salt intake.

Just to get your bearings, a high sodium intake is considered to be about 5000 mg/day – the average intake in China. Intakes in many western countries are moderate by comparison, about 3300-3700 mg/day. However, the upper limit of sodium intake recommended in Australia’s Nutrient Reference Values is only 2300mg/day, the same figure recommended in the Dietary Guidelines for Americans. Just last week the European Society of Hypertension and the European Society of Cardiology published new guidelines for the management of hypertension, recommending sodium intakes in the range of approximately 2000-2300 mg/day. The American Heart Association goes even further, recommending just 1500 mg/day.

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Lowering sodium intake has been a constant in dietary guidelines for decades and is widely recommended as part of healthy eating advice. The conventional view is that eating too much sodium increases blood pressure and thereby increases the risk for cardiovascular disease. Yet the benefits of sodium reduction are being hotly debated with experts around the globe trading arguments in journals, on-line debates and the mainstream media. What’s driving this debate? 

In November 2011, O’Donnell and colleagues published a study on the relationship between urinary sodium and the risk for cardiovascular disease. Urinary sodium is a good way to estimate how much sodium people are eating as, generally speaking, ‘sodium in equals sodium out’. As higher sodium intake is known to be linked with higher blood pressure, the expectation might have been that the higher the sodium excretion, the higher the risk for cardiovascular disease. However, the relationship turned out to be J-shaped. In other words, high intakes of sodium were indeed associated with higher risk for cardiovascular disease, but so were low intakes of sodium. How can that be? Does eating too little sodium cause harm?

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