London School of Hygiene & Tropical Medicine

A large-scale analysis of the effect of dietary salt reduction on deaths and illness from cardiovascular disease (CVD) in adults has been inconclusive, according to a new report.

The Cochrane Collaboration review - co-authored by Professor Shah Ebrahim, of the London School of Hygiene & Tropical Medicine - found no strong evidence that salt reduction reduced all-cause mortality or morbidity from CVD in people with normal or high blood pressure, or heart failure. Although the sodium reduction did produce a small blood pressure decline, there was insufficient evidence to determine whether this reduction of salt intake increased or decreased cardiovascular mortality. The review has been co-published in the American Journal of Hypertension and the Cochrane Library.

Dietary salt intake has been identified as a potential risk factor for heart disease and many public health agencies and government guidelines advise people to cut their salt intake by half. In the face of scientific uncertainty surrounding these recommendations, the University of Exeter's Rod Taylor and colleagues including Professor Ebrahim undertook a systematic review of the effect of dietary salt reduction on mortality and CVD morbidity in adults with normal and high blood pressure, and those with heart failure.

Through a rigorous search process, they were able to identify only seven randomized controlled trials (RCTs), comprising 6,520 participants, for meta-analysis. The single heart failure study found a significantly increased mortality in those allocated to the lower sodium diet. Nevertheless, sodium intake did not significantly influence mortality in the studies taken together. Based upon their findings, the Cochrane authors support the recent call for further rigorous, large, long-term RCTs, capable of definitively demonstrating the CVD benefit of dietary salt reduction. They also recommend evaluation of the effects of reducing the sodium content of processed food.

Prof Ebrahim says: "These findings should not be misinterpreted as showing that salt reduction will not save lives. There was insufficient evidence to make this judgment. Giving advice to reduce salt is a weak method of reducing salt intake in the population. Reducing hidden salt in processed foods, including bread, would likely have a bigger impact on blood pressure levels and on cardiovascular disease."

• Taylor RS, Ashton KE, Moxham T, Hooper L, Ebrahim S. Reduced dietary salt for the prevention of cardiovascular disease. Cochrane Database of Systematic Reviews 2011, Issue 7. Art. No.: CD009217. DOI: 10.1002/14651858.CD009217.
• 'Reduced Dietary Salt for the Prevention of Cardiovascular Disease: A Meta-Analysis of Randomized Controlled Trials (Cochrane Review)' by Taylor et al: DOI: 10.1038/ajh.2011.115.