Salt sensitivity increases the risk of death, whether or not a person has high blood pressure

Dr Myron Weinberger

Some estimates suggest that up to a quarter of people who have normal blood pressure are actually salt-sensitive.

This means that instead of excreting excess salt away in the urine, the body actively retains much of it via the kidneys.

The latest research, by the National Heart, Lung and Blood Institute, looked at 25-year-old tests for salt sensitivity carried out on more than 700 patients.

Salt sensitivity had been checked by giving them a saline solution followed by a diuretic drug, and looking for subtle variations in blood pressure and volume over the following two days.

The team looked at the progress of those patients and found that 123 of them had died from cardiovascular disease or another cause.

People who had normal blood pressure at the time of the first test, but were salt-sensitive, fared no better than those who had high blood pressure from the outset, even though it would have been expected that hypertensive patients would have done worse.

Cutting back on salt

Dr Myron Weinberger, who led the study, said: "Salt sensitivity increases the risk of death, whether or not a person has high blood pressure.

"We can take advantage of this finding. They don't need to drastically cut back on salt intake to reduce their risk of death.

"We should be careful about the sodium content in prepared, preserved, and processed foods."

British experts looking for the secrets of salt sensitivity have found genetic differences in the key part of the kidney which controls the amount of salt reabsorbed from the urine.

One genetic flaw which has been identified in people who suffer a severe form of this sensitivity means the kidney has far too many "sodium channels", openings through which the sodium ions can pass from the urine back into the body.

Dr Geoff Sandle, from the University of Leeds, told BBC News Online: "Between 80% and 85% of those diagnosed with high blood pressure have it for no discernable reason

"It is possible that in some of these, the condition has a genetic basis.

"But there are many factors which control the way the body regulates the amount of sodium."