Human Nutrition 3(3+0)

Lesson 44 : Bioavailability and Ion Absorption Electrolyte Balance

Potassium

Potassium performs functions similar to those of sodium, except that it is the main positive ion found inside(intracellular), cells. Potassium is vital to fluid balance and nerve transmission. The potassium content of foodstuffs is very variable. (2 GRAPH)

Intake of potassium:
The intake of K+ is largely from diet with some contribution from drinking water. Natural diets provide from 50 to 150 mEq. K/day. Most of the common foods contain moderate amounts. Cereals (including rice and wheat), cheese, eggs, fats and almost all fresh fruits contain less than 8 mEq. K/100g. and have been used in planning low potassium diets.

Table: Potassium balance in man (m moles/day)

Source	Potassium input	Source	Potassium output
Food and water	100-400	Sweat Faeces Urine	a
			b
			100-400
Total	100-400		100-400

a and b – 5% loss through sweat and faeces

Output of potassium:
Excretion of potassium is through sweat, faeces and urine, Urinary excretion alone accounts for 95% of the total intake. The output of potassium in the urine closely reflects the dietary intake. The adreno- cortical hormones cause increased potassium excretion in the urine. Excessive production of aldosterone causes large losses of potassium in the urine and consequent deficiency in the cells and a low level in the blood.

• Increased potassium concentration is known as hyperkalemia. Since potassium is normally excreted by the kidneys, disorders that decrease the function of the kidneys can result in hyperkalemia. Certain medications may also predispose an individual to hyperkalemia.

• Hypokalemia, or decreased potassium, can arise due to kidney diseases; excessive loss due to heavy sweating, vomiting, or diarrhea, eating disorders, certain medications, or other causes.

 

The normal blood potassium level is 3.5 - 5.0 milliEquivalents/liter (mEq/L), or in international units, 3.5 - 5.0 millimoles/liter (mmol/L).