Salt’s harmful effects may extend to artery hardening

The study, published in the American Journal of Clinical Nutrition​, deepens our understanding of the detrimental effects of excessive salt consumption, which has led to pressure on the food industry to reformulate foods with lower sodium content.

“We hypothesized that if dietary salt restriction improves arterial vascular tone and blood pressure, then the converse should also occur, ie, increased salt intake would lead to a deterioration in arterial vascular tone,”​ wrote the researchers, led by Dr Rob Walker from the University of Otago in New Zealand.

“Confirmation of these changes would provide further supporting evidence of a role of dietary sodium restriction in the outpatient management of hypertensive individuals,”​ they added.

In collaboration with scientists from Deakin University in Australia, and the University of Colorado in the US, the University of Otago researchers report that people with hypertension participating in a low salt intervention period experienced significant increases in blood pressure when the salt content of their diets was increased. In addition, a correlation between salt and pulse wave velocity (PWV), a measure of the stiffness of the arteries, was observed, suggesting an effect on vascular health independent of blood pressure.

The researchers noted that their study was relatively small (only 35 people participated) and short (four weeks) and therefore need support in longer trials with other populations, particularly those at high risk like the obese, diabetics, and people with kidney disease.

Despite such caveats, Dr Walker and his co-workers state that their findings “confirm the potentially detrimental effects of a high dietary salt intake, with increases in blood pressure and PWVevident within a short time frame”​.

Salt – a little but not too much​

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.

And with 80 per cent of salt intake coming from processed foods, many countries have initiated salt reduction programmes, with many holding up the UK’s Food Standards Agency as the torch bearer for national initiatives.

The benefits of a salt global salt reduction strategy were given blinding clarity by a meta-analysis published in The Lancet Chronic Diseases Series in 2007, which concluded that reducing salt intake around the world by 15 per cent could prevent almost nine million deaths between 2006 and 2015.

Study details​

Thirty-five people with hypertension participated in the study, which involved an initial two week intervention with a low-sodium diet (60 mmol per day). After this time, the participants were randomly assigned to one of three groups in a cross-over manner: The low-salt diets were maintained by supplemented with a sodium-free tomato juice, a tomato juice containing 90 mmol of sodium, or a tomato juice containing 140 mmol of sodium.

After having participated in all three interventions, comparisons showed that PWV was higher following both sodium interventions in the order of about 0.37 m/s. Furthermore, systolic and diastolic blood pressure increased in both sodium groups, by 4.4 and 2.4 mmHg, respectively in the 90 mmol of sodium group, and by 5.6 and 3.3 mmHg, respectively in the 140 mmol sodium group.

“The major finding was that increased sodium (salt) intake to levels currently consumed in the Western diet in subjects consuming a low-salt diet caused an increase in PWV and blood pressure,”​ wrote the researchers.

Commenting on the research, Professor Graham MacGregor, salt reduction campaigner and professor of cardiovascular medicine at the Wolfson Institute of Preventive Medicine, Barts & London NHS Trust, welcomed the study as adding to the body of science supporting the benefits of salt reductions. Prof MacGregor told FoodNavigator: “There is a whole lot of knowledge coming in that shows that salt not only affects blood pressure, but also vascular health.”​

Source: American Journal of Clinical Nutrition​
Published online ahead of print, doi: 10.3945/ajcn.2009.28645
“Dietary salt loading impairs arterial vascular reactivity”​
Authors: A.S. Todd, R.J. MacGinley, J.B.W. Schollum, R.J. Johnson, S.M. Williams, W.H.F. Sutherland, J.I. Mann, R.J. Walker