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High salt intake may have immediate effects on circulation: Study

By Nathan Gray , 07-Feb-2011

Consuming highly salty foods may begin to impair the functioning of blood vessels within 30 minutes, according to new research published in the American Journal of Clinical Nutrition.

The study suggests that 3.8 grams of salt – an amount similar to commonly eaten meals – can reduce the ability of blood vessels to widen after a meal when compared with a lower salt meal. The researchers found raised levels of salt from the diet can significantly reduce flow mediated dilation (a measure of blood vessels ability to widen) within 30 minutes.

Researchers from the Commonwealth Scientific and Industrial Research Organization (CSIRO), Australia report that when a high salt meal was consumed blood vessels widened about half as much as for low salt meal, though they noted that these effects passed after around two hours when normal functioning was restored.

“What surprised us was that this is similar to responses seen after a meal high in saturated fats, which we know can be damage blood vessels in the long-term,” said the study’s lead author, Kacie Dickinson.

“These results suggest that high salt intakes have acute adverse effects on vascular dilatation in the postprandial [post meal] state,” said the researchers.

Salt risks

Dickinson and her colleagues said that there is “compelling evidence” to show a link between salt intake, increased blood pressure, and risk of cardiovascular disease (CVD).

The researchers said that impaired blood vessel functioning (endothelial dysfunction) is considered to be an initial step in the development of atherosclerosis, which has been previously shown to be induced by metabolic factors – through an increase in oxidative stress and a reduction in the bioavailability of nitric oxide. The endothelium is the layer of cells lining blood vessels.

High salt intakes, even over a short period of time, are known to lead to similar reduction in nitric oxide, and increases in oxidative stress – however Dickinson and her co- workers said that whether blood vessel functions are impaired after a high salt meal have not been studied.

“Determining whether a high salt meal has a detrimental effect on endothelial function in the postprandial [post meal] state is of interest given the high levels of nondiscretionary salt consumed in foods and typical meals,” they said.

The new study investigated the vascular responses of a group of healthy adults to a high-salt meal containing 65 mmol sodium and low-salt control meal containing 5 mmol sodium.

Study details

The researchers studied the impact of short-term salt intake in sixteen healthy volunteers. The postprandial effect of dietary salt on endothelial function was measured by flow-mediated dilatation (FMD) and blood pressure. FMD is often used by scientists to assess endothelial function: Impaired FMD response is a CVD risk factor and can precede clinically symptomatic CVD by many years.

Flow mediated dilation was found to decrease after both the high and low salt meals, but was significantly more impaired after the high salt meal than the low salt.

The authors reported that measures of FMD were significantly reduced after 30 minutes and one hour for the high salt meal – with the greatest impairment in function occurring one hour after the meal was ingested.

The impairment in flow mediated dilation in response to the high salt meal was said to be of a similar magnitude to that shown in healthy subjects after a meal high in saturated fats.

Despite the differences in salt intake and observed changes in FMD, Dickinson and colleagues did not observe any significant changes blood pressure between the high and low salt meals.

They added that they found no evidence to suggest that blood pressure is involved in the mechanism by which salt impairs the endothelial functioning.

Mechanisms

“It may be plausible that the 65-mmol sodium load (3.8 g salt) in the current study induced changes in endothelial function via alterations in plasma sodium …A repeat of the current study including plasma sodium samples and other parameters of endothelial function, such as nitric oxide and eNOS would confirm this,” suggested the authors.

They said that the study suggests that high salt intakes may have acute, adverse effects on the ability of blood vessels to widen after in the post meal phase.

Dickinson and colleagues added that it is unclear whether the observed effects have long-term consequences on the risk of atherosclerosis and cardiovascular disease, but said that the results contribute to a body of research showing non blood pressure related effects of high salt intakes.

Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.110.006155
“Endothelial function is impaired after a high-salt meal in healthy subjects”
Authors K.M. Dickinson, P.M. Clifton, J.B. Keogh

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