Behind the Headlines: Is salt good for you?
“Salt is safe to eat and cutting our daily intake does nothing to lower the risk of suffering from heart disease,” says the Daily Express.
The newspaper goes on to say that the findings are a blow to NICE which has been calling for salt reduction measures to help cut the number of deaths from cardiovascular disease (CVD) by up to 40,000.
The Daily Mail also reported yesterday that cutting down on salt will not make you healthier and that the findings contradict all recommendations by the Government and medical profession urging the public to reduce the amount of salt they consume.
Where did the story come from?
The stories are based on a review paper published this week in the Cochrane Library entitled: Reduced dietary salt for the prevention of CVD.
The Cochrane Library is a collection of six databases that contain different types of independent evidence to inform healthcare decision-making.
This review paper, carried out by researchers at the University of Exeter, looked at the data from 7 previously published randomised controlled trials that assessed the long-term (over six-months) effects of interventions aimed at reducing dietary salt on mortality and cardiovascular morbidity. This meta-analysis involved a total of 6,489 participants.
Three of the studies involved people with normal blood pressure (normotensives), two with patients who had hypertension, one in a mixed population of normal and hypertensive patients, and one study which included patients with heart failure.
The researchers found small reductions in salt intake, associated with small reductions in blood pressure, consistent with other salt reduction studies. They concluded that because of the size of the studies there was not enough information to understand the effect of these changes in salt intake on deaths or cardiovascular disease.
They add that limitations to the evidence base in this review mean that the conclusions regarding the effect of a reduction in dietary salt may not be robust.
Professor Shah Ebrahim, one of the study researchers, says: "Our results should not be used as evidence that salt reduction is a waste of time or does no good - a conclusion several newspapers made wrongly.
"Our results suggest that giving advice to reduce salt intake is not as effective as we might hope. Therefore we need to use population-based strategies involving reductions in hidden salt in processed foods, including bread, and salt reductions in food outlets at work and in schools."
What have other studies found?
As the researchers point out in their paper, other papers have found clearer links between salt reduction and cardiovascular events.
They cite research conducted in 2009 which looked at prospective observational studies that examined the relationship between dietary sodium and cardiovascular events.
This study included 13 cohort studies (177,025 participants) over a follow up of three-17 years and found higher salt intake to be associated with greater risk of stroke.
Elsewhere, researchers from the University of California found that eating smaller amounts of salt every day as a teenager could help to reduce high blood pressure and lower the risk of heart disease and stroke in adulthood.
Using computer modelling, they projected that reducing daily salt intake by 3g could result in a 44 to 63 per cent reduction in the number of teenagers and young adults with hypertension. This amounts to up to 550,000 fewer cases of hypertension.
The authors of the review conclude that: “Our findings are consistent with the belief that salt reduction is beneficial in normotensive and hypertensive people.
“However, the methods of achieving salt reduction in the trials included in our review, and other systematic reviews, were relatively modest in their impact on sodium excretion and on blood pressure levels, generally required considerable efforts to implement and would not be expected to have major impacts on the burden of CVD.
“The challenge for clinical and public health practice is to find more effective interventions for reducing salt intake that are both practicable and inexpensive.”
What does NICE recommend?
NICE published guidance in June 2010 calling for an acceleration of the reduction in salt in the general population from a maximum intake of 6g per day per adult by 2015 and 3g by 2025.
Professor Mike Kelly, Public Health Director at NICE, says: “This guidance aims to save lives and reduce the terrible toll of ill health caused by heart disease and stroke. Making the simple changes recommended could prevent around 40,000 premature deaths in people aged under 75 each year.”
Professor Simon Capewell, Vice Chair of the guidance group and a public health physician in Liverpool, says: “There has been encouraging progress in reducing the level of salt and saturated fats in our diet over the last 10 years, but the rate of change needs to be speeded up urgently.
“The benefits of doing this will be seen remarkably quickly, within 2-3 years, along with corresponding savings to the NHS. And there's also clear evidence that cutting dietary salt levels works: it's already been done in Japan and Finland, and the USA is also taking action.”
Commenting on this latest research, Professor Capewell, adds: "The main Cochrane message is that advice to individuals only succeeds in getting them to reduce their salt intake a little. This is not a new finding.
"Crucially, it does not change the public health consensus from the WHO, PAHO, NICE etc, which is that dietary salt raises blood pressure (this is bad), reducing dietary salt intake lowers blood pressure (this is good), and that government actions are far more effective and cost saving at reducing dietary salt intake, than is advice to individuals."
Professor Mike Kelly indicates that “On the basis of this one review NICE will not be altering its current recommendations on salt”.
7 July 2011