Public health advice to minimise salt consumption to lower blood pressure is based on spurious science and does not recognise the complex role of sodium in the body, say scientists whose study attacks the basis of dietary guidelines.

As health authorities consider slashing salt recommendations to even lower levels, the most comprehensive survey of salt intake in the US found consumption there had not changed in more than 40 years, despite the recent rise of low-sodium foods, and the average was at least 50 per cent higher than the recommended maximum.

As well, there was relatively little difference between the high and low ends of the salt intake spectrum – suggesting people naturally gravitate towards a similar amount of dietary salt, regardless of changes in food processing.

The research, led by the eminent Harvard researcher Walter Willett, re-analysed all studies between 1957 and 2003 that measured sodium levels in urine – a more accurate method than asking people what foods they ate.

Professor Willett said the finding that salt intake had not changed, while the prevalence of high blood pressure had risen, suggested the ”epidemic of obesity may be a more plausible determinant” of high blood pressure rates than salt.

His study, published yesterday in the American Journal of Clinical Nutrition, joins an international survey released last year with similar findings.

That study’s author, David McCarron, said taken together the research indicated blanket public recommendations to eat a low salt diet, aimed at all people and not just those at highest risk of heart disease, were ”doomed to failure”.

Three-quarters of most people’s salt intake is thought to come from processed food, and many health authorities believe persuading manufacturers to lower salt content would benefit health. But Dr McCarron said ”working against that theoretical outcome is the reality that over millennia … sodium was added to food at the time of preservation, cooking or consumption,” and if salt were removed from processing people might simply seek it elsewhere.

The stable and ostensibly high salt consumption seen in the studies might be just ”evidence of a ‘normal’ range of dietary sodium intake in humans that is consistent with our understanding” of the functions of salt, such as its regulation of blood volume, Dr McCarron said.

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