Features: QED

Take it with a pinch of salt

(Filed: 27/04/2005)

Robert Matthews investigates the debate over high-salt diets

We may no longer spend our weekends watching witches being ducked, but we still seem to need demons to vilify. Ageing crones with crooked noses have been replaced by multinational industries, hell-bent on doing us harm with everything from radioactive waste to dodgy silicone implants.

The latest hate figure is the global food industry, whose brews and potions are widely held to have turned millions of us into lard mountains. Fortunately, we can count on the Government’s armies of Witchfinders General to protect us from the forces of evil, and last week one of its most diligent agents, the Food Standards Agency, scored a victory over that cabal of mass-poisoners known as the Salt Manufacturers’ Association.

The trade organisation had complained about a television advertising campaign that ran last autumn aimed at persuading us to reduce our intake of salt. Featuring a character called Sid the Slug, the FSA’s advertisements warned that high blood pressure, heart disease and strokes had been linked to the consumption of too much salt, with Sid yelling that “too much salt can lead to a heart attack!”. The SMA complained to the Advertising Standards Authority that the campaign was at best meaningless and at worst highly misleading, as it implied that salt was necessarily bad for health and should be reduced.

Well, the SMA would say that, wouldn’t it? As the ASA made clear in its adjudication rejecting the complaint, there is a wealth of scientific evidence showing that high salt intake poses a serious risk to cardiac health. So who could possibly argue with the central message that we should all cut down on salt?

Pretty much anyone who has read the scientific literature, which reveals this argument to be a non sequitur – and a potentially dangerous one. A high-salt diet has indeed been linked to high blood pressure, increased arterial thickness, strokes and increased severity of cardiac failure. Yet as the SMA pointed out, what does “high” actually mean? Certainly the evidence that most ordinary people will get any benefit from reducing salt intake is far from compelling.

In 2003, the British Medical Journal carried out a review of studies into the long-term effects of reduced salt intake among both ordinary people and those with high blood pressure. The researchers identified a dozen studies that followed patients on reduced salt diets for up to seven years.

Overall, the results showed that a low-salt diet did have some effect on blood pressure. It amounted to just one millimetre of mercury – well below levels regarded as clinically significant, not least because most family doctors’ blood pressure monitors can’t measure to that precision. As for differences in death rates or heart attack rates, none was found – despite the fact that the reduced salt regimes were far more draconian than even the FSA would impose on us. The researchers concluded that official efforts to persuade us to cut down on salt would produce small reductions in individual risk, though when multiplied across the whole nation, the total effect might be worth having.

More significant, however, were their caveats even on this feeble support for the official line. The researchers pointed out that increased blood pressure is only one risk factor for cardiovascular disease in any case, adding that “overall clinical benefits [or harms] of a low sodium diet are unclear”.

In other words, not only is there little evidence that cutting salt will bring health benefits, it is even possible that it could do more harm than good. Salt is a source of sodium, which is critical to the functioning of living cells. Inadequate levels of sodium – hyponatremia – produce a host of potentially life-threatening effects including confusion, fatigue, seizures, coma and death.

It is recognised as a problem for the very old and the very young and is a leading cause of death among marathon runners – who drink so much water that they dilute their sodium to lethal levels. The long-term effect of attempts to persuade us all to cut our intake of this vital element are a mystery. In the absence of any large-scale scientific studies, there is simply no good scientific evidence to confirm that the benefits exceed the risks.

This is especially worrying given that the anti-salt campaign appears to be working. According to a recent FSA survey, about 45 per cent of us are actively trying to cut down on salt. Fortunately, the Government has yet to introduce measures to force us to comply with this latest decree on public health. Until some decent evidence emerges for the benefits of bland, salt-free food, claims to the contrary should be taken cum grano salis.

Salt Association Logo Salt Association Logo