Without it, nerves and muscles would cease to function, the absorption of major nutrients would be impaired, and the body would not be able to maintain adequate water and mineral balance. In a complex way, increased salt intake causes more fluid to be contained in the blood vessels. This increased volume of blood requires the heart to work harder to pump blood to all the tissues in the body. Increasing the blood's volume within the enclosure of the circulatory system is one way that salt increases blood pressure. Another way salt helps elevate blood pressure is through the action of the arterioles.
Arterioles are blood vessels that dilate and constrict to regulate blood pressure and blood flow.
By contracting under the influence of sodium, arterioles effectively increase the resistance to blood movement and lessen the volume of blood that is returned to the heart. This action also increases blood pressure. Other mechanisms linking sodium with hypertension are less well understood. The extent to which each person responds to high intakes of salt is probably genetically determined. Some people are more susceptible to the effects of sodium than others, and sodium sensitivity appears to increase with age.