Too much sodium can lead to a number of illnesses, the most common of
which is hypertension (high blood pressure). This is because sodium
helps regulate how much water is retained in the body's cells and
blood - and if there's too much fluid retained in the blood then the
pressure on the arteries/veins increases. A similar problem is "edema"
(the medical term for swelling) - particularly in the fluid around the
brain. Here are some sites that talk about the link between increased
salt intake and hypertension:
Rutgers University: Sodium
"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 bloods volume within the enclosure of the
circulatory system is one way that salt increases blood pressure.
Another way salt may help 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 intake 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."
Colorado State University: Sodium in the Diet
"Sodium intake is one factor involved in the development of high blood
pressure, otherwise known as hypertension."
"Women who consume excess sodium may be at higher risk for developing
osteoporosis even if calcium intake is adequate."
The disease hypernatremia (excessive sodium) is generally caused by
too little fluid rather than too much salt intake:
Penn State A to Z Health Topics: Hypernatremia
"Symptoms of hypernatremia depend upon the cause. When water is lost
through diarrhea or vomiting, for example, the patient urinates very
little, with the small amounts of urine produced having a dark yellow
color. If hypernatremia is caused by kidney dysfunction, the patient
urinates large quantities of clear urine, much like water. When the
sodium concentration in the blood is extremely high, it affects the
brain cells. As this occurs, the patient experiences muscle twitching,
and begins to feel tired and confused. Eventually, severe
hypernatremia can lead to coma and death, especially in young children
and the elderly."
I did a number of Google searches to find these sites, using
variations on the following keywords:
Again, please let me know if I can clarify anything in this answer further!