Sunday, November 10, 2013

Low sodium intake: beneficial or toxic? By Jerry Brainum

No one thinks much about salt or sodium chloride these days, except in what happens when you consume too much. Sodium is linked to water retention and a bloated appearance. Medical doctors warn their patients that consuming too much sodium will raise blood pressure, and thus increase the risk of heart attacks and strokes. In fact, having hypertension or high blood pressure is the number one risk factor for strokes. But the concern about sodium or salt hasn't always been this way. In ancient times, salt was considerable so valuable that wars were fought over it. It was considered more valuable than gold at one point.Indeed, the word "salary," is derived from the Latin word for salt, and Roman soldiers were paid with salt. Small wonder that the popular phrase,"worth his salt" is said of a particularly productive person.  Homer (the Greek poet, not the TV cartoon character) called salt "a divine substance." His opinion was echoed by the philosopher, Plato, who noted that "salt is especially dear to the gods." The word "salt" appears more than 50 times in the bible. So it's clear that at times, salt has been revered in history.
   Not so today. Despite sodium being an essential mineral, health warnings abound about the consequences of too much sodium in the diet. At first, these warnings seem accurate, since sodium is ubiquitous in the food supply, particularly in processed and fast foods, which are packed with salt. The question is: how much sodium do we actually need to ingest to stay healthy?  According to the Center for Nutrition Policy and Promotion, the daily intake of sodium should be less than 2,300 milligrams a day in normal people, and 1,500 milligrams a day in those at greater risk for cardiovascular disease, including people over 50, black people, and those with existing high blood pressure, type-2 diabetes, and kidney disease. The American Heart Association recently suggested that ideal cardiovascular health could be achieved for most people by 2020, and one way to do this is to limit sodium intake to less than 1,500 milligrams a day. The average person ingests 3,300 milligrams of sodium a day, while our paleolithic ancestors averaged only 768 milligrams daily intake of sodium. The minimal sodium requirement is thought to be around 500 milligrams.
  Sodium regulates extracellular fluid, including that found in the blood, which is 98% water. Sodium is also vital for nerve transmission, and nerve signals are propagated when sodium and potassium are exchanged in nerve cells. This explains one of the primary signs of low sodium: muscle cramps, as the nerve conductivity to muscle is blunted with lack of sufficient sodium intake, or by using drugs such as diuretics that promote sodium excretion. Besides muscle cramps, other symptoms of sodium depletion include loss of appetite,  nausea, and fatigue. The initial fatigue often felt during low carbohydrate diets occurs because of a loss of stored glycogen caused by the lack of carb intake. Glycogen is stored with water, and as glycogen is depleted the water portion is excreted, along with various minerals, including sodium. The lack of minerals adversely affects nerve transmission and brain function, leading to fatigue.
   It's not common to be deficient in sodium, but it's possible if you engage in certain practices. For example, drinking excessive distilled water can lead to hyponatremia, or low sodium body stores. This has happened to long distance runners who consume copious amounts of sodium-free water during a race. In 2007, a young woman rapidly drank two gallons of distilled water during a radio contest, then promptly died from brain edema due to sodium depletion. Of course, using diuretic drugs, which work by promoting the loss of water through fostering sodium and other mineral excretion, can also rapidly cause sodium depletion. This can lead to either intense muscle cramps, or in a worst-case scenario, death. Several deaths in bodybuilders has occurred because of their use of potent diuretic drugs combined with lack of sodium intake.
  Contrary to popular belief, however, the body normally tightly controls sodium levels. With a high intake of sodium, the extracellular fluid intake expands, leading to a temporary rise in blood pressure. The higher blood pressure increases perfusion of blood through the kidneys (which depend on a higher blood pressure to properly filter the blood) this increased blood perfusion then stimulates the kidneys to excrete sodium. The body prevents the excretion of too much sodium through the release of an adrenal hormone called aldosterone, which retains sodium and water, while promoting potassium excretion. In fact, the human body has evolved to retain sodium, while promoting potassium excretion.
   It's important to note that in all the studies that have shown protective effects induced by a reduction in sodium intake, the proof was in the form of surrogate or indirect markers of sodium metabolism, such as increased excretion of sodium. The degree of blood pressure lowering by diets designed to lower sodium has been trivial at best, with no proof that such diets actually prevent high blood pressure or cardiovascular disease (CVD). However, there is evidence that a low sodium diet can be detrimental under certain conditions, such as if a person has type-2 diabetes. Persons with diabetes who ingest low sodium diets show higher rates of cardiovascular disease and mortality. How can this be? A low sodium intake stimulates activity of the sympathetic nervous system, which then overstimulates the heart.In addition, low sodium activates the  renin-angiotensin-aldosterone axis, which paradoxically increases, rather than lowers blood pressure, and also exerts direct damage to the arteries, thus promoting atherosclerosis. Perhaps the most curious effect of all, however, is that low sodium intake increases insulin resistance. Diabetics already have a problem with insulin resistance, which itself is known as "pre-diabetes." Thus, having a diabetic ingest a low sodium diet is like putting oil on a fire.
   People with congestive heart failure are often advised to follow a low sodium diet, since a primary cause of congestive heart failure is long-standing high blood pressure. Yet those afflicted with CHF show reduced blood perfusion in the kidneys, which activates the sympathetic nervous system, along with the renin/angiotensin/aldosterone axis. This causes a retention of water at the expense of sodium, which is then rapidly excreted, leading to possible hyponatremia. Studies show that CHF patients who ingest a low sodium diet have a higher mortality rate compared to those who consume a normal sodium intake. Consider that in rat studies, the rodents show a 4-times greater rate of arterial plaque formation when on a low sodium intake compared to normal intakes. The effect is blocked when the rats are provided with an ACE-inhibitor drug, which blocks the renin/angiotensin effect.  Mouse studies show that a low sodium diet increases vascular inflammation and promotes atherosclerosis.
   A recent review of 167 studies that examined the effects of a low sodium diet found that such diets increased renin, aldosterone, noradrenaline, adrenalin, cholesterol and triglycerides, thus painting a picture showing increased CVD risk from low sodium diets. Consider that prior to the introduction of iodized salt, thyroid disease due to lack of sufficient  dietary iodine, which is required for the synthesis of thyroid hormones, was prevalent in the United States, especially in the so-called "goiter belt," in the midwest. Salt in food not only increases palatability,but also exerts an antimicrobial effect. Decreasing salt intake may lead to increased food-borne infections.
   So how should you handle sodium intake? For most people, a normal intake of up to 4 to 6 grams of sodium a day won't cause any problems. This is especially true if you also ingest sufficient potassium, which balances the effects of sodium in the body. In fact, potassium will speed the excretion of excess sodium intake if you ingest a 2:1 ratio of sodium to potassium. Thus, if you consume 2,000 milligrams of sodium, ingesting 1,000 milligrams of potassium will offset any possibly deleterious effects of the sodium intake, including effects on water retention and blood pressure. Adding other minerals, especially calcium and magnesium, will further completely neutralize any possible problems associated with a high sodium intake. And consider one other fact about sodium: sodium is the primary activator of the amino acid transport in muscles that permits uptake of amino acids for use in muscle protein synthesis reactions. Thus, protein supplements that feature "low sodium" is idiotic. Sodium also activates the sodium/potassium pump in muscle that turns on the creatine transport protein, which determines how much creatine is taken up into muscle.

                                                           Sodium occurrence in foods

©,2013 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited.

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