A study published online this week in the American Journal of Hypertension has rubbed salt in the wounds of the old belief that excessive salt intake contributes to the development of cardiovascular disease
A group of researchers from the University of Exeter in England analyzed the results of seven clinical studies. Collectively these studies involved over 6,000 adults who had been tracked for at least six months. Patients were assigned to one of three groups, according to whether they had:
- Normal blood pressure
- Heart failure
All patients were evaluated to determine how their dietary salt intake was associated with blood pressure, incidence of heart disease, and death. Subsequent meta-analysis of the combined data from these studies, however, failed to obtain any firm evidence that reducing dietary salt intake prevents the chances of death from cardiovascular disease. Reduced salt intake did tend to reduce blood pressure a little, although it had no effect on reducing the rate of cardiac arrest, stroke, or heart surgery.
The National Salt Reduction Initiative
The World Health Organization currently recommends a maximum salt intake of 5 grams per day, whereas many people in western countries often ingest twice this amount. And indeed the FDA currently suggests not ingesting more than a teaspoon of salt a day – almost 2.5 grams. Although they recommend that people should be trying to reduce their salt use in food, they additionally advise the food industry to remove excess salt from their products. Almost 80% of the salt in our diets apparently derives from that which is added to processed foods and drinks before they are sold.
Such public health initiatives to reduce salt consumption are mostly based on observational studies that have shown a connection between high sodium intake and increased risk of cardiac disease. Such study types, however, are not designed to demonstrate a cause-and-effect relationship – they are only able to show association, and any association could potentially be explained by numerous other factors.
This new report thus introduces more controversy on conventional thinking that a reduced salt intake can prevent heart disease. Subsequently the researchers of this most recent report conclude that additional research is required to clarify the association between heart disease and salt intake – and in particular, larger randomized controlled trials would be beneficial.
Taylor RS et al: Reduced Dietary Salt for the Prevention of Cardiovascular Disease: A Meta-Analysis of Randomized Controlled Trials (Cochrane review). (2011) Am J Hypertens, July 6 [Epub ahead of print]