The new study suggests that the risks associated with a high salt intake go beyond the risk of high blood pressure (hypertension) – and could actually cause direct harm to vital organs including the heart and brain.
Writing in the Journal of The American College of Cardiology (JACC), the team behind the new study noted that the concept of ‘salt sensitive’ blood pressure is gaining recognition as more people realise that blood pressure (BP) responses to dietary salt intake vary from person to person – and that in some dietary salt intake has little to no effect on BP.
Led by Dr William Farquhar from the University of Delaware College of Health Sciences, the new study points to evidence of adverse effects on multiple target organs and tissues, even for people who are salt resistant. Indeed, recent pre-clinical and clinical data have shown that that even in the absence of an increase in BP, excess dietary sodium can have damaging effects on including the blood vessels, heart, kidneys, and brain.
"Chronically elevated dietary sodium may 'sensitize' sympathetic neurons in the brain, causing a greater response to a variety of stimuli, including skeletal muscle contraction," said Farquhar. "Even if blood pressure isn't increased, chronically increased sympathetic outflow may have harmful effects on target organs."
"High dietary sodium can also lead to left ventricular hypertrophy, or enlargement of the muscle tissue that makes up the wall of the heart's main pumping chamber," added study co-author Dr David Edwards. "As the walls of the chamber grow thicker, they become less compliant and eventually are unable to pump as forcefully as a healthy heart."
Farquhar and Edwards also noted that previous work in the area has suggested that excess salt intake in humans impairs endothelium-dependent dilation, while another study demonstrated that dietary sodium loading impairs microvascular function.
In both cases, the effects are independent of changes in blood pressure.
Regarding the kidneys, evidence suggests that high sodium is associated with reduced renal function, a decline observed with only a minimal increase in blood pressure, they said.