Why is salt "bad"?

ShawnD

Why is it that people sometimes must limit their salt intake? After my uncle had a heart attack, he was told to cut back on salt as much as possible. Why?

Moonbear

For people who have high blood pressure, salt can worsen the condition. In most people, extra salt is just excreted, but in some people, their body just doesn't do that properly, and instead the salt stays around and increases water retention in the body, which raises blood pressure, or worsens already high blood pressure.

nautica

Water moves across membranes into an area of higher salt concentration. So with a higher salt concentration, you have a higher water content, which increases the volume of blood, which in turn increases the pressure.

Moonbear, I have a question.

If Na ions move in the opposite direction as K ions, could a person supplement with K and decrease blood pressure????

I know that K is used as a Na replacement in "No salt" and that bodybuilders will replace salt with K before a competition to help flush water, but do you think this would have an impact on blood pressure??? I would think that theoritically it should, but it would seem to simple of a rememdy for blood pressure. Also, is there a theory why water moves in the direction of Na ions, instead of K ions or does it move in the direction of both based on the total concentration of Na outside vs. K inside.

Thanks
Nautica

hitssquad

Climacteric. 2003 Oct;6 Suppl 3:36-48.

Potassium: more beneficial effects.

He FJ, MacGregor GA.

Blood Pressure Unit, St. George's Hospital Medical School, London, UK.

Over 70 years ago, potassium was found to have a natriuretic effect and was used in patients with heart failure. However, it took many years for its role in the control of blood pressure to be recognized. Recently, epidemiological and clinical studies in man and experimental studies in animals have shown that increasing potassium intake towers blood pressure and that communities with a high potassium intake tend to have lower population blood pressures. Several studies have shown an interaction between salt intake and potassium intake. However, the recent DASH-Sodium (Dietary Approaches to Stop Hypertension) study demonstrates an additive effect of a low salt and high potassium diet on blood pressure. Increasing potassium intake may have other beneficial effects, for example, reducing the risk of stroke and preventing the development of renal disease independent of its effect on blood pressure. A high potassium intake reduces calcium excretion and could play an important role in the management of hypercalciuria and kidney stone formation, as well as bone demineralization. Potassium intake may also play an important role in carbohydrate intolerance. A reduced serum potassium increases the risk of lethal ventricular arrhythmias in those at risk, i.e. patients with ischemic heart disease, heart failure or left ventricular hypertrophy, and increasing potassium intake may prevent this. In this article, we address the evidence for the important role of potassium intake in regulating blood pressure and other beneficial effects of potassium which may be independent of and additional to its effect on blood pressure.

PMID: 15018247

Moonbear

Well, I'm glad someone else answered that question, because I didn't know the answer myself. All I know related to potassium and high blood pressure is that for those taking diuretics to treat hypertension, a side effect is depletion of potassium, so those patients are recommended to take potassium supplements or eat foods high in potassium. Too low of potassium can result in a lot of problems due to nervous system malfunction (that's why there is an increased risk of ventricular arrhythmia with potassium deficiency...poor conductance across the heart to keep everything synchronized).

I'm not sure if there's a reason for water to preferentially move toward sodium vs potassium, and I think it's the latter explantion of total ion concentration on each side of a membrane determining which way the water goes.

ShawnD

Wow. Great post, hit.


Sodium is the one kept out of cells and potassium is the one inside cells right?

hitssquad

I think so (if you mean sodium is kept at a low level in cells and potassium is kept at a high level in cells):

• Our cells live in an ocean of salt water (serum) which is very high in sodium and very low in potassium. This salt water passes through each cell at the rate of nearly 100 times the volume of the cell each second. Yet the cells themselves contain a sodium concentration of only 7% of the serum and a potassium concentration 32 times greater than the serum.
  
  To explain this discrepancy in the 1940s researchers invented the idea of the "sodium pump" which they suggested might continually pump excess sodium out of the cell and perhaps carry potassium in.
  
  Gilbert Ling discovered that the sodium pump was never a theory or even a hypothesis but merely a rephrasing of observations that became accepted as fact, without any concrete facts to support its existence.