Bernard Lown, MD
Adhering to a healthy life style requires understanding some basic facts of biology and nutrition. In this age of market medicine we are constantly bombarded with products that we do not need but persuaded that we can not live without. An effective defense against such hype is to be guided by sound information culled from scientific studies.
This essay aims to provide a scientific perspective on a vital mineral.Salt, though an essential component of our daily diet, is a much neglected subject. It is extraordinarily ordinary, yet is indispensable to preserving health. Salt is the universal currency that purchases stability of the inner fluid environment in our bodies. All living things require saltto hold on to water.
Salt is a combination of two chemical elements: sodium, a potential culprit, and chlorine, an innocent fellow traveler.These two elements are wedded inseparably in the body.
It is hard to imagine that during most of recorded history, table salt was scarce and wars were waged over its possession. Various lines of evidence suggest that salt, was introduced during the Neolithic period, some five to ten thousand years ago.
Habitual use of salt, as food preservative or additive to enhance taste, is intimately connected with advances from nomadic to agricultural life. The first mining of salt goes back to Austrian Tyrol during the Bronze Age about one thousand years before the present era.
Ancient historic records are filled with references to the preciousness of salt:
• Nearly three thousand years ago, Homer called salt “divine.”
• Salt was a part in many religious cults, folklores, and superstitions. Bread and salt offerings commonly served to propitiate the Gods.
• The Bible speaks of a covenant of salt as an enduring pact.
• Salt played a prime role in commerce. Even in contemporary times cakes of salt have been used as money in Ethiopia and Tibet.
• Roman legionnaires trod to collect their pay and a regular ration of salt on one of Italy’s oldest roads, Via Salaria, — whence derives our word salary.
• At banquets during feudal times the salt cellar was a centerpiece placed close to the lord of the manor. To be seated at the table “above the salt” was a sign of rank and favor.
• To this very day, expressions such as “salt of the earth” or “worth his salt” refer to sterling character; while to “eat a man’s salt” conveys establishing a binding relationship and enduring friendship.
• Over many centuries urine, due to its salinity, was believed to possess therapeutic properties and usedas a medicinal agent.
Some Biologic Facts
Several billion years ago the oceans covered the entire globe. In these murky hot waters the earliest sprouts of unicellular organisms launched the miraculous journey of life. To survive they had to be in harmony with the all engulfing ocean environment.
As organisms became multi-cellular and grew in complexity, they incorporated little bits of ocean to bathe every cell. To this very day, the innards of all living things are bathed in primordial ocean.
The concentration of sodium is identical throughout the entire animal kingdom. The tissues of frogs and fish, snakes and birds, dolphins and polar bears, elephants as well as humans, all haveidentical salt. concentration. This is powerful testimony of our shared ancestry and common beginnings. While we think of ourselves as composed of muscle and bone, actually we are largely salt water – nearly 80% of our substance is nothing but brine.
Once animals crawled on to land, they were urgently challenged how the amount lost daily whether through waste excretion, sweat or tears had to be replaced.
Over millions of years, the evolutionary process bequeathed terrestrial creatures with a remarkable series of thermostat-like structures to conserve sodium. These spectacular sensors continuously monitor and protect the constancy of the inner bathing fluid. In fact the concentration of sodium barely varies over a lifetime. The kidneys are the prime regulators, the ultimate magicians, who have mastered the fine art of conserving each pinch of salt. Even when one is chronically and terminally ill, the body integrating circuitry maintains the constancy of sodium concentration.
Without retaining salt, humans could not maintain their circulating volume of blood. Such stability enables our erect posture and bodily adjustment of blood pressure The brain is specially sensitive to changes in blood flow and helps coordinate the signaling to maintain the constancy of our inner environment. We have all suffered symptoms of salt and water deficiency. For example, on hot days or after vigorous exercise, we have experienced dry mouth, thirst, wooziness, or light- headedness. Suchsymptoms are due to a loss of salt and water.
If salt is so essential for survival, why then is it deemed hazardous?
The Hazard of Excess Salt
To understand this seeming conundrum, a little more biological history needs to be addressed. In the forest primeval, where our ancestors roamed, among the great threats to survival was bleeding due to trauma, attacks by predatory animals, or inadequate salt availability. Under these life threatening circumstances, to conserve an adequate circulating volume of blood, the kidneys mastered a unique system of conserving sodium.
This remarkable adaptation was demonstrated in experiments conducted during WWII. To prepare American troops to fight in hot climates, for several months military volunteers worked intensively in the Nevada desert while subsisting on a low salt diet. Their intake of sodium was limited to 50 mg daily, a mere one hundredth of what they were accustomed.Impressively, the kidneys cut down sodium excretion below this daily minuscule intake.
Three entirely novel developments have thrown this evolutionary adaptation of kilter. In the first place the daily sodium intake has increased by a factor of of one hundred or more. This relates to the fact that sodium is tasty and “addicting.” Furthermore with emergence of mass marketing of food requiring long distance transport and long shelve lives, sodium in various guises provedeffective preservative. Manufactureres have utilized these two factors to heavily dose their food products with an abunadance of salt.
Patients with serious heart disease curtail the pumping of blood. Biologic sensors throughout the body interpret this as a reduced blood volume. The kidneys are signaled to conserve every atom of sodium, resulting in retention of salt and water. This results in swelling of legs and congestion of lungs.
Since the normal diet is very high in salt- in large part from the addition of sodium to promote shelf life of many foods – excess fluid is accumulated, enhancing even further the burden of the already strained heart muscle. A daily American diet usually contains ten to twenty grams of salt (about fifty- to one-hundred-fold the minimum requirement for health).
When the retained fluid concentrates in the extremities, the ungainly edema presents little hazard.The legs may feel heavy, walking is tiring, and shoes are ill-fitting. But, if the fluid is sequestered in the lungs, one experiences breathlessness, insomnia, and exhaustion.
With more fluid retention, life-threatening congestion may ensue, with resulting diminished oxygen flow to vital organs. While powerful diuretics are now available to protect against such dire consequences, reducing the sodium in the diet is essential.
Excessive salt intake is also a ajor factor in the risingprevalence to high blood pressure,. A large body of evidence links hypertension to salt intake. For example, the highest incidence of high blood pressure is in Northern Japan where inhabitants subsist on salted fish. Wherever populations reduced salt intake, blood pressure is notably lowered.
The problem of hypertension is formidable. Beyond age of sixty-five, nearly 65% of Americans have hypertension. With age, the body grows more susceptible to the adverse effects of salt.
The consensus of informed medical opinion is for all people to reduce their salt intake. Not only are vdirect wear and tear of vessels, but there is growing evidence Furthermore, reduction of sodium intake and the ensuing lowering of blood pressure protects blood vessels from arteriosclerosis.
The question posed at the outset is readily answered: salt is the very stuff of life, but when consumed immoderately, it shortens life. The Athenians twenty-five hundred years ago already grasped the essence when they counseled meden agan — , nothing in excess.
*future essays will address the problem of salt and high blood pressure.