Salted_ A Manifesto on the World's Most Essential Mineral, With Recipes - Mark Bitterman [17]
You can eliminate almost any single food or group of foods from your diet and still survive. Abstain from apples, and you will live. Abstain from all fruit, and you will live. Abstain from all plants, for that matter, and you will live. Or eat no meat and no animal by-products, and you will still live. But you cannot live without salt.
Dissolved in the water of your body, dietary salt exists as sodium and chlorine ions (chloride). For every ten grams of salt you eat, four grams are sodium and six are chloride. We use the sodium in salt to regulate how water functions within our bodies and, not coincidentally, we use water to regulate the body’s concentration of salt. The human body boasts three distinct fluid systems: blood plasma, extracellular fluid, and lymphatic fluid—all salted. The concentration of sodium ions in the blood is directly related to the regulation of all these bodily fluid levels. Sodium performs dozens of functions in the body, mainly to do with fluid regulation, nerve and muscle function, and digestion; it carries water and nutrients into and out of cells; it helps regulate blood pressure and fluid volume; it helps with the function of blood vessels and other membranes.
Salt and water form a system that supports innumerable physiological processes; they’re bound together as intimately and mysteriously as life itself. Even our thoughts are made of salt. The 100 billion neurons in your brain each contain about a million chemical pumps, each of which is capable of transporting hundreds of positively charged sodium and potassium ions per second to maintain higher concentrations of potassium ions inside the cells and higher levels of sodium outside. Specialized channels allow potassium to leak out of the cells at a slightly faster rate than sodium leaks in. This polarizes the membrane of the nerve cell, giving it a negative electrical potential, which in turn encourages sodium ions to enter the cell. When the ions are allowed in, the cell is depolarized; this cycle repeats every two milliseconds (0.002 seconds). The transition between the influx and efflux of sodium and potassium ions is called the action potential of the neuron—and makes up the electrical activity of your brain and the rest of your nervous system.
In the body, sodium works in tandem with potassium, the two major cations (positively charged ions) making up the body’s salts. Sodium mainly permeates the fluid between cells (plasma) and the blood, providing the saline bath and nutrition necessary for the cells to thrive. Potassium, on the other hand, is retained mainly within the cells (in the intracellular fluid). There are about 157 potassium ions and just 14 sodium ions in intracellular fluid compared to 143 sodium and 4 potassium in interstitial fluids (blood) and 152 sodium and 5 potassium in plasma. (The major intercellular anions, or negatively charged ions, are phosphate and protein. The major anion in blood and plasma is chloride.) The body expends a tremendous amount of energy maintaining the balance of potassium and sodium inside and outside of the cells—recall the sodium and potassium pumps powering the electrical activity of our nerves. The presence of both in their proper balance supports nerve function and muscle contraction and relaxation, and regulates the permeability of the cell membrane, affecting how nutrients, water, and waste are transported to and from cells. Deficiency of one or the other compromises this process and hurts the cell. We regularly lose sodium through the excretion of urine, through our skin when we sweat, and in the production of stomach acid (hydrochloric acid). If we don’t eat enough sodium every day, we will rapidly run low.
If you have too little sodium in your body, you are in trouble. Sodium deficiency, or hyponatremia, can cause headache, nausea and vomiting, muscle spasms and seizures, heart arrhythmia, decreased consciousness, or coma. Sodium deficiency among people with high blood pressure increases the risk of heart attack. One of the most serious possible effects of hyponatremia is swelling