The study, published in Hypertension Research, suggests that salt intake may cause a conflict for the cardiovascular system as it attempts to simultaneously maintain blood pressure and temperature homeostasis.
“It appears that salt sensitive individuals maintain core body temperature equilibrium more effectively than salt resistant individuals, but experience increased blood pressure in the process,” said Dr. Robert Blankfield, clinical professor of family medicine at Case Western Reserve University School of Medicine, and lead author of the study.
“Conversely, salt resistant individuals maintain blood pressure equilibrium more effectively than salt sensitive individuals following salt and water intake, but experience a greater temperature reduction in the process,” he added
It is known that certain people often referred to as ‘salt sensitive’ experience an increase in blood pressure following the ingestion of salt, whereas other ‘salt resistant’ people do not.
Researchers have been unable to explain why some individuals are salt sensitive and others are salt resistant, and what causes such differences.
Previous research has suggested that blood pressure responses to dietary sodium (sodium sensitivity) may vary among individuals may be at least partially determined by individual genetic predisposition.
However, since the cardiovascular system is responsible for maintaining normal blood pressure and also helps control body temperature by conducting heat from the muscles and internal organs to the skin's surface, the team of researchers tested whether these dual roles of the cardiovascular system might help explain how salt ingestion leads to salt-sensitive hypertension.
Blankfield and his colleagues examined the effect of salt and water consumption versus just water in a group of 22 healthy men without high blood pressure.
Participants' blood pressure, rectal temperature, cardiac index (the volume of blood pumped by the heart per minute), and urine output were monitored after intake of either water or salt and water.
The researchers reported that the ingestion of salt and water lowered body temperature more than the ingestion of water alone.
In addition they found that body temperature decreased more in individuals who are salt resistant than in individuals who are salt sensitive.
“Salt and water loading raises blood pressure in salt sensitive individuals, and the elevated blood pressure persists for a finite period of time during and after the salt and water intake,” said Dr Matthew Muller, first author of the paper.
“These transient blood pressure elevations, whether brief or prolonged, might initiate the complex changes within the walls of the arteries and arterioles that characterize individuals with essential hypertension,” he explained.
“Our findings are consistent with the hypothesis that salt intake causes conflict for the cardiovascular system in terms of simultaneously maintaining blood pressure and temperature homeostasis,” wrote the researchers.
They added that a better understanding of the causes of essential hypertension “has proven elusive, in part because it has not been possible to explain what distinguishes salt sensitive from salt resistant individuals.”
“If our results are generalizable, it would be possible to account for the role of sodium chloride in the development of salt sensitive hypertension,” they concluded.
Source: Hypertension Research
Published online ahead of print, doi:10.1038/hr.2011.27
“Effect of acute salt ingestion upon core temperature in healthy men”
Authors: M.D. Muller, E.J. Ryan, D.M. Bellar, C.H. Kim, M.E. Williamson, E.L. Glickman, R.P. Blankfield