Research proves the dangers of salt

May 10 2005

Sydney University scientists have proved that salt has a dangerous adrenalin-inducing effect on people suffering from high blood pressure, or 'hypertension'.

When people get a fright, their sympathetic nervous system is activated and they experience a rush of adrenalin. But people with high blood pressure experience a sustained increase in sympathetic nerve activity when they consume dietary salt, according to US Fulbright scholar Dr Virginia Brooks and Professor Roger Dampney (pictured) from Sydney's Department of Physiology.

Their collaborative research has produced new data to support the hypothesis that dietary salt activates the brain in hypertension sufferers, producing sustained increases in sympathetic nerve activity, or what is commonly called the 'fight/flight' response.

The consequences of uncontrolled hypertension are broad and extremely serious, including strokes, heart attacks, and heart and kidney failure. Around 28 per cent of the Australian population suffers from a blood pressure of more than 120/80.

Dr Brooks, from the Oregon Health and Science University in the United States and currently based at Sydney, said: "It has long been suspected that salt activates the brain in people suffering from hypertension by increasing salt concentration in the blood. Our research has generated actual empirical information to support this."

In healthy people, sympathetic nerve activity might occur for a few seconds with an accompanying surge of adrenalin. The heart rate increases and the blood vessels are constricted. However, people with high blood pressure appear to experience sustained increases in such activity, sometimes lasting months or years, and this increase is exaggerated with increased dietary salt.

"Despite the research so far, we have been unable to understand why increased salt increases blood pressure in people who have hypertension," said Dr Brooks.

By monitoring hormonal factors that act on the brain after increasing dietary salt, Professor Dampney and Dr Brooks are more clearly defining the cause of this activity, and will test a hypothesis concerning the mechanism in the brain that generates the particular neural response.

Professor Dampney said: "We suspect that a nucleus within the hypothalmus plays a central role, the hypothalmus being the region that controls vital unconscious elements such as body temperature, blood pressure regulation and glucose levels. We are testing the extent to which low levels of nitric-oxide gas - normally a neuron inhibitor - increase sympathetic neural activity in sufferers of high blood pressure."

The research of Professor Dampney and Dr Brooks could lead to effective treatments for hypertension and its associated problems.

The project complements their expertise, combining Professor Dampney's research into brain control of the nervous system and Dr Brooks's research into hypertension.