Blood pressure (BP) in people with the metabolic syndrome is particularly sensitive to salt intake, indicates research suggesting that sodium reduction might be effective in managing hypertension in people with multiple cardiometabolic risk factors.
The finding is reported by US researchers in The Lancet and is based on a dietary intervention study investigating the association between BP and salt sensitivity in 1906 Chinese adults.
At baseline all participants were free of diabetes but 283 had the metabolic syndrome. They received a low-sodium diet (51.3 mmol/day) for 7 days followed by a high-sodium diet (307.8 mmol/day) for 7 days, with BP being measured at baseline and throughout each intervention.
Jing Chen (Tulane University School of Medicine, New Orleans, Louisiana) and fellow investigators detected a “strong, positive, and significant’ association between the metabolic syndrome and salt sensitivity of BP, defined as a decrease in mean arterial blood pressure of >5 mmHg during low-sodium or an increase of >5 mmHg during high-sodium intervention.
After adjusting for multiple confounders, BP changes were significantly greater in people with the metabolic syndrome than in those without during both the low-sodium and high-sodium diets (p<0.0001 for all comparisons).
Furthermore, the likelihood of salt-sensitivity rose with increasing numbers of risk factors for the metabolic syndrome. Compared with those with no risk factors, participants with four or five risk factors had a 3.54-fold and 3.13-fold increased risk for high salt-sensitivity during the low-sodium and high-sodium diets, respectively.
Chen et al say that the underlying mechanism of increased salt sensitivity in individuals with the metabolic syndrome is not fully understood. One possibility is that insulin resistance and concomitant compensatory hyperinsulinemia might lead to sodium retention and extracellular fluid volume expansion, thereby increasing BP responses to sodium intake.
“A reduced intake of sodium could be beneficial in individuals with metabolic syndrome,” the investigators write. “We now need to establish the effect of prevention and treatment of metabolic risk factors on salt sensitivity of blood pressure.”
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