Reducing the intake of salt from the diet may improve the health of blood vessels, with the effects going beyond blood pressure benefits, says a new study.
Short-term adherence to a low salt diet was associated with a 1.5 per cent increase in flow-mediated dilation (FMD), the measure of a blood vessel's healthy ability to relax, according to results published in the new issue of the American Journal of Clinical Nutrition.
Australian researchers also report that blood pressure improved as a result of the low-salt diet, but that there was no link between the blood pressure improvements and FMD.
The study looks set to maintain the pressure on food formulators to reduce the salt content of their products.
Salt is of course a vital nutrient and is necessary for the body to function, but campaigners for salt reduction, like the Consensus Action on Salt and Health (CASH) consider the average daily salt consumption in the western world, between 10 and 12g, far too high.
Numerous scientists are convinced that high salt intake is responsible for increasing blood pressure (hypertension), a major risk factor for cardiovascular disease (CVD) - a condition that causes almost 50 per cent of deaths in Europe.
The pressure has been mounting on food manufacturers to reduce the salt content of their foods and the UK's Food Standards Agency's (FSA) recommendation of six grams of salt per day for the general population is understood to be more a realistic target for the next five years than the ideal healthy limit.
Researchers from the CSIRO Human Nutrition and Flinders University in South Australia recruited 29 overweight and obese men and women with normal blood pressure. The average age of the participants was 52.7 and their average BMI was 31.6 kg/m2. The participants were randomly assigned to either a low salt diet or a US diet for two weeks, followed by two weeks of no intervention, and they then crossed over to the other diet for two more weeks.
According to the researchers, both diets contained similar levels of potassium and saturated fat and were designed to ensure that the weight of the participants remained stabile.
At the end of the six-weeks of study, the researchers, led by Jennifer Keogh, report that FMD was 4.89 per cent in the low-salt group, and 3.37 per cent in the US diet group.
Furthermore, the systolic blood pressure of the participants was significantly lower following the LS diet (112 mmHg) compared to following the US diet (117 mmHg).
Excretion of sodium was also significantly lower following the low salt diet, compared to the US diet, added Keogh and her co-workers.
“The main finding of this study was that a sodium-restricted diet improved endothelial function, assessed by FMD, relative to a US diet in overweight and obese normotensive subjects,” wrote the researchers. “Change in FMD was unrelated to changes in BP, which suggests that a mechanism other than change in BP is responsible for the effect of salt on FMD.”
Keogh and her co-workers speculated that the endothelial effects may occur via a neurohumoral response, by preventing the production of cortisol, a stress hormone reported to increase blood pressure. They indicated that this hypothesis should be investigated by a prospective study.
The study was financed by CSIRO Human Nutrition.
Source: American Journal of Clinical Nutrition
Volume 89, Pages 485-90
“Effects of a low-salt diet on flow-mediated dilatation in humans”
Authors: K.M. Dickinson, J.B. Keogh, P.M. Clifton