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Nutrition Notes Topics

Sodium (Na) and Potassium (K)

Life began in the ocean. Sea salts in water remain the milieu of all living cells. The main sea-water salt, sodium chloride (NaCl), is the critical determinant of body fluids - held at 0.9% concentration in the human body, sodium intake must neither be deficient nor excessive for the body to function well.

North American diets tend to offer sodium levels higher than actual need (minimum of 1100 mg/day, adults). Large salt surpluses are the result of high intake of commercially prepared food, and salt added at the table. Food usually contains enough sodium salts to supply our needs, and added salt tends to be surplus.

Salt and sugar are the two nutrients for which we have a specific appetite. The adaptation to high salt intake seems to involve cravings and compulsive eating of salted foods. The opposite adaptation occurs with reduced salt intake - cravings for salt disappear, and heavily salted foods become unpalatable.

Sodium is the major cation in extracellular fluid. Sodium concentration in plasma is maintained in healthy individuals within the narrow range of 135 to 145 mmol/L, balanced between sodium intake and output. Hyponatremia is defined as a serum sodium concentration less than 135 mmol/L. Common causes of hyponatremia are reduced sodium intake from food; increased sodium loss in urine, feces, or sweat; and water retention as in patients with kidney failure, nephrotic syndrome, or inappropriate anti-diuretic hormone secretion. Hyponatremia can be life threatening and requires immediate medical attention

Reduced sodium intake is considered a primary strategy of reducing high blood pressure. Increased intake of calcium and potassium may lower high blood pressure and extra potassium may protect against stroke-associated death. North American diets tend to offer sodium levels 10-20 times higher than actual need. To lower sodium intake, commercially prepared foods are avoided, and restraint is recommended in the use of table salt in cooking and at the table. Table salt also supplies iodide; salt restriction may decrease iodide intake below RDA, and necessitate the addition of iodide to the supplement list.

The American Heart Association guidelines for hypertension hypertension (2006) recommended salt intake be lowered to about 65 mmol/day sodium (corresponding to 1.5 g/day sodium or 3.8 g/day of sodium chloride). Because more than 80% of consumed salt comes from processed foods, the American Medical association called on food manufacturers to reduce salts in food by 50% over the coming 10 years. In 2007 the AMA recommended a 50% reduction in the amount of sodium in processed and restaurant foods. They confirmed that the link between sodium consumption, high blood pressure, and cardiovascular disease is solidly established. Between the ages of 25 and 55 years a 1.3 gm per day reduction in sodium intake would save about 150 000 lives. Populations with an average sodium ingestion of less than 1400 mg/day have no progressive increase in blood pressure with age. In the US, average sodium consumption has been estimated to be 4000 mg/day per 2000 kcal.

The proper ratio of Sodium to Potassium is close to 1. Most diets have sodium disproportion with the ratio tending toward sodium excess at more than 3 to 1. Potassium intakes of up to 4000 mg per day are reasonable. Sodium intake should be below 2000 mg/day. When you switch to low sodium foods, some added sodium salt may be required with potassium supplements to achieve optimal intake if sodium and potassium loss increases because of sweating or from vomiting and/or diarrhea. Potassium chloride (KCl) is sold as a "salt substitute". KCl does not taste the same as regular salt and is best used in cooking rather than added to food at the table. Potassium supplements are also available in pill and liquid form. Tablets of potassium chloride (KCl) tend to irritate the small bowel, and may cause surface ulceration. KCl as the free salt or dissolved in water is the preferred potassium preparations. Manufacturers should add iodide to the potassium salt (KCl) to imitate regular iodized salt.