Potassium is, like sodium , a mineral element. It is mainly found in plants but unlike sodium, rarely in the form of chloride, rather in the form of bicarbonate, citrate or phosphate.
It constitutes, with sodium , the element which plays the most important role in the electrical activity of cells (where it is essentially found):
- it regulates the nervous condition,
- it controls muscle contraction and participates in particular in the functioning of the heart rhythm ,
- it regulates the body's water content.
This is due to the fact that potassium (symbol K) is involved in the same functions as sodium (symbol Na) with a complementary role. The balance between potassium and sodium is fundamental: when one goes up, the other goes down.
Having too much sodium (which is already a problem in itself) is necessarily accompanied by an insufficient level of potassium.
However, a potassium deficit induces many disturbances, as we will explain.
There is a sodium-potassium pump at the level of cell membranes which plays a key role in maintaining the resting potential of nerve, muscle and heart cells.
This pump makes it possible to exchange the sodium ions (Na+), coming from the intracellular medium, with the potassium ions (K+), coming from the extracellular medium, in a precise ratio of 3Na+ for 2 K+.
All living beings (even single-celled beings) have one.
It is at the origin of all energy transformation: for a molecule of sugar or calcium to penetrate into each of the cells of an organism, it needs a companion: a sodium atom. And this sodium pump acts at the level of all our cells (each of them constituting a “mini-factory” which functions independently of all the others).
Originally, our diet was low in sodium and high in potassium, in accordance with the needs of our body. Today we consume ten times more salt and four times less potassium than our ancestors and the sodium-potassium ratio is unbalanced.
Potassium and high blood pressure
To survive, our body needs salt because it feeds, as we briefly saw above, the sodium pump providing energy to our body, but a diet too rich in salt promotes water retention. , edema formation and arterial hypertension .
It is the presence of potassium that will allow the elimination of sodium once it has done its job in the cell. If the latter remained swollen with sodium and water, it could no longer function.
Increasing potassium intake lowers blood pressure , apparently both through potassium's ability to increase sodium excretion and through its vasoactive (dilating) effects on blood vessels.
For good regulation of blood pressure , it is therefore necessary to face the following dietary challenge every day: no excess sodium and enough potassium.
Currently, the WHO recommends limiting salt intake (at most 5 grams per day) and increasing potassium intake (at least 3.5 g per day). These recommendations seem unrealistic in view of modern life, but they give a direction to follow.
Be careful though, this rule does not necessarily apply to patients with kidney problems , who have more difficulty eliminating potassium and in whom a high potassium level could induce heart rhythm disorders .
Potassium and kidney failure
The role of the kidneys is to eliminate all the “waste” found in the blood. During kidney failure , the kidney is gradually no longer able to properly eliminate proteins , salt , potassium and phosphorus .
We understood that the role of potassium was essential in the functioning of our body, but the concentration of potassium in the blood plasma (called kalemia ) must remain within a very precise range: a normal level of potassium in the blood in adults is between 3.6 and 5.0 mmol/L.
An accumulation of potassium in the blood, called hyperkalemia , caused by the defect in the renal excretion of potassium, creates a significant risk of arrhythmias and conductive disorders which can lead (in the most serious cases and in the absence of urgent treatment ) to cardio-circulatory arrest.
A potassium deficiency, called hypokalaemia, contributes to hypertonia of the arterioles and their hyperactivity to vasoactive hormones, as well as to sodium retention and calcium loss (a diet rich in potassium would reduce the risk of stroke in postmenopausal women).
It should be noted that a subject on diuretics , permanent laxatives or certain other less common drugs, or an anorexic or bulimic subject, is automatically in a situation of potassium deficiency.
In general, the organism is rather better protected against hyperkalaemia (too much potassium) than against hypokalaemia (not enough potassium), with the exception, however, of the case of the subject with renal insufficiency for whom too much amount of potassium in the blood poses a life-threatening risk.