Blood Pressure: Benefits of salt reduction clear, despite brain claim

Benefits of salt reduction clear, despite brain claim
By Stephen Daniells, 16-Oct-2009

Related topics: Science & Nutrition, Preservatives and acidulants

Public policy to reduce salt intake has clear health benefits, despite claims that intake is physiologically determined and cannot be controlled by policy, says a UK expert.

A new study published in the Clinical Journal of the American Society of Nephrology (CJASN) questions the scientific logic and feasibility of the decades-long effort to limit salt intake, claiming that such policies have not reduced salt intakes because sodium appetite is controlled by the brain.

Evaluation of 24-hour urinary sodium excretion, the standard measure of daily sodium intake, in 19,151 individuals collected in 62 previously published surveys from 33 countries worldwide revealed that daily sodium intake across a wide range of ‘food environments’ was in the "relatively narrow range" 2,700 to 4,900 mg, leading the authors to conclude that salt appetite is physiologically controlled, despite measures in some countries to curb intake.

“It is unrealistic to attempt to regulate America's sodium consumption through public policy when it appears that our bodies naturally dictate how much sodium we consume to maintain a physiologically set normal range,” said lead author David McCarron, MD, from the University of California, Davis.

Missing the issue

Speaking to FoodNavigator, Graham MacGregor, salt reduction campaigner and professor of cardiovascular medicine at St. George's University of London, dismissed the article as totally missing the issue.

In countries like the UK, Ireland and the USA, over 80 per cent of salt intake comes from processed food, and people therefore do not realize they are consuming it.

Professor MacGregor was recently involved in the largest double-blind trial of modest salt reduction in a free-living population, which showed that moderate reductions do indeed result in clinically relevant and beneficial reductions in blood pressure.

The study, published in the American Heart Association’s Hypertension journal found that reducing salt intake from 9.7 to 6.5 grams per day reduced average blood pressure from 146/91 to 141/88 mmHg within six weeks.

Recommendations

Salt is of course a vital nutrient and is necessary for the body to function, but the average daily salt consumption in the western world, between 10 and 12g, vastly exceeds recommendations from WHO/FAO of 5 grams per day to control blood pressure levels and reduce hypertension prevalence and related health risks in populations.

McCarron and co-author Judith Stern admit to having previously consulted with the food industry and the Salt Institute. Their article is published at a time when the Institute of Medicine is convening to discuss salt reduction strategies. It also questions measures set in place by many national bodies, including the UK’s Food Standards Agency (FSA), which has set targets of 6 grams per day.

The food industry has responded to the FSA targets and is successfully reducing the salt content in many formulations.

The UK’s policy has been “most successful” said MacGregor, with 2008 statistics showing that salt intake in the UK since the introduction of the FSA’s targets in 2004 has been reduced by one gram. “The vast majority of the population is not aware that the salt has been taken out of their foods,” he added.

Indeed, a spokesperson for the FSA told FoodNavigator: "The article states that UK survey data shows no change in sodium intakes over 25 years. It is important to remember that the Agency’s salt work only started in 2004 and that a reduction in salt intakes of 0.9g per day between 2000 and 2008 has been seen."

This equates to saving over 6,000 premature deaths and £1.5bn to the economy each year, added the spokesperson.

“Frankly, [McCarron’s] article contains no evidence that reducing salt intake is not beneficial,” said MacGregor. “If such measures were introduced in the US it would reduce the number of deaths from heart disease and stroke by 150,000 a year.”

The FSA spokesperson added: "This study does not change FSA advice that adults should eat no more than 6g of salt a day and that children should have even less."

Eight million souls

While such a figure is impressive, it pales in comparison with global figures. A meta-analysis published in The Lancet Chronic Diseases Series in 2007 concluded that reducing salt intake around the world by 15 per cent could prevent almost nine million deaths between 2006 and 2015.

Source: Clinical Journal of the American Society of Nephrology
Published online ahead of print, doi: 10.2215/CJN.04660709
"Can Dietary Sodium Intake Be Modified By Public Policy?"
Authors: D.A. McCarron, J.C. Geerling, A.G. Kazaks, J.S. Stern
To access the paper for free, please click here. http://cjasn.asnjournals.org/cgi/reprint/CJN.04660709v1