DR. S.M. ALAM & M.A. KHAN
May 2 - 15, 2011
Sodium chloride also known as table salt, rock salt, common salt or halite is a mineral composed primarily of sodium and chlorine. It is essential for human diet, animal life in small quantities, but is harmful to human, animals, and plants in excess. The taste of salt (saltiness) is one of the basic human tastes. It is produced in different forms: unrefined salt (such as sea salt), refined salt (table salt), and iodized salt. It is a crystalline solid, white, pale pink or light gray in color, normally obtained from seawater or rock deposits. Edible rock salts may be slightly grayish in color because of mineral content. Chloride and sodium ions, the two major components of salt, are needed by all known living creatures in small quantities.
Sodium chloride is essential to life on Earth. Most biological tissues and body fluids contain a varying amount of salt. The concentration of sodium ions in the blood is directly related to the regulation of safe body-fluid levels. Propagation of nerve impulses by signal transduction is regulated by sodium ions. A 0.9 per cent sodium chloride in water is called a physiological solution because it is isosmotic with blood plasma. It is known medically as normal saline. Physiological solution is the mainstay of fluid replacement therapy that is widely used in medicine in prevention or treatment of dehydration or as an intravenous therapy to prevent hypovolemic shock. Humans are unusual among primates in secreting large amounts of salt by sweating.
Salt's preservative ability was a foundation of civilization. It eliminated dependency on the seasonal availability of food and allowed travel over long distances. By the Middle Ages, caravans consisting of as many as forty thousand camels traversed four hundred miles of the Sahara bearing salt, sometimes trading it for slaves. Until the 1900s, salt was one of the prime movers of national economies and wars. Salt has played a prominent role in determining the power and location of the world's great cities. Timbuktu was once a huge salt market. Liverpool rose from just a port to Ireland to become the prime producer of the world's salt in the 1800s.
SALT CREATED AND DESTROYED EMPIRES
The salt mines of Poland led to a vast kingdom in the 1500s, only to be destroyed when Germans brought sea salt. Venice fought and won a war with Genoa over salt. Christopher Columbus and Giovanni Caboto destroyed the Mediterranean trade by introducing the new world to the market. Salt was once one of the most valuable commodities known to man. Salt was taxed from as far back as the 20th century BC in China. In the Roman Empire, salt was sometimes even used as a currency, giving in the term of salary. The Roman Republic and Empire controlled the price of salt, increasing it to raise money for wars, or lowering it to be sure that the poorest citizens could easily afford this important part of the diet. Throughout much of history, it influenced the conduct of wars, the fiscal policies of governments and even the inception of revolutions.
In the empire of Mali, merchants in 12th-century Timbuktu-the gateway to the Sahara Desert and the seat of scholars-valued salt enough to buy it for its weight in gold; this trade led to the legends of the incredibly wealthy city of Timbuktu, and fueled inflation in Europe, which was exporting the salt. Jordanian and Israeli salt evaporation ponds at the south end of the Dead Sea.
Now a days, salt is produced by evaporation of seawater or brine from other sources, such as brine wells and salt lakes, and by mining rock salt, called halite. While most people are familiar with the many uses of salt in cooking, they might be unaware that salt is used in a plethora of applications, from manufacturing pulp and paper to setting dyes in textiles and fabric, to producing soaps and detergents. In the northern USA, large quantities of rock salt are used to help clear highways of ice during winter.
Many microorganisms cannot live in an overly salty environment: water is drawn out of their cells by osmosis. For this reason, salt is used to preserve some foods, such as smoked bacon or fish. It has also been used to disinfect wounds. While salt was a scarce commodity in history, industrialized production has now made salt plentiful.
The salt one buys for consumption today is not purely sodium chloride as most people assume. In 1924, trace amounts of iodine in form of sodium iodide, potassium iodide or potassium iodate were first added, creating iodized salt to reduce the incidence of simple goiter. Salty soil is generally unfit for agriculture, hence the practice of salting the earth. Due to its high concentration of salt, the Dead Sea has such a high density that some objects which are not normally buoyant can float on its surface. Humans float easily, having a density slightly less than that of pure water. (But only 8 per cent of the salt in the Dead Sea is sodium chloride, 53 per cent is magnesium chloride, 37 per cent potassium chloride).
Sodium is a component of salt, 2.5 grams of salt provides 1 gram of sodium. Although salt is the major source of sodium in our food, sodium is also a component of other ingredients, such as sodium bicarbonate used in baking and monosodium glutamate used as a flavor enhancer. Too much sodium in the diet can lead to health problems. It is one of the risk factors that contribute towards high blood pressure (hypertension), which substantially increases the risk of developing heart disease or stroke. In the UK, most people are eating more salt than is good for their health and a reduction in average intake to 6 grams (which is equivalent to 2.5 g of sodium) per day has been recommended.
Salt is involved in regulating the water content (fluid balance) of the body. The sodium ion itself is used for electrical signaling in the nervous system. However, too much salt increases the risk of health problems, including high blood pressure. Therefore, health authorities have recommended limitations of dietary sodium. Sodium is one of the primary electrolytes in the body. All four cationic electrolytes (sodium, potassium, magnesium, and calcium) are available in unrefined salt, as are other vital minerals needed for optimal bodily function. Too much or too little salt in the diet can lead to muscle cramps, dizziness, or electrolyte disturbance, which can cause neurological problems, or death. Drinking too much water, with insufficient salt intake, puts a person at risk of water intoxication (hyponatremia). Salt is sometimes used as a health aid, such as in treatment of dysautonomia.
Excess salt consumption is linked with a number of conditions including:
* Stroke and cardiovascular disease.
* Hypertension (high blood pressure): "Since 1994, the evidence of an association between dietary salt intakes and blood pressure has increased. The data have been consistent in various study populations and across the age range in adults." A large-scale study from 2007 has shown that people with high-normal blood pressure who significantly reduced the amount of salt in diet decreased the chances of developing cardiovascular disease by 25 per cent over the following 10 to 15 years.
* Left ventricular hypertrophy (cardiac enlargement): "Evidence suggests that high salt intake causes left ventricular hypertrophy, a strong risk factor for cardiovascular disease, independently of blood pressure effects. And, there is accumulating evidence that high salt intake predicts left ventricular hypertrophy. Excessive salt (sodium) intake, combined with an inadequate intake of water, can cause hypernatremia. It can exacerbate renal disease.
* Edema: A decrease in salt intake has been suggested to treat edema (fluid retention).
* Duodenal ulcers and gastric ulcers.
* Gastric cancer (stomach cancer) is associated with high levels of sodium, "but the evidence does not generally relate to foods typically consumed in the UK." However, in Japan, salt consumption is higher.
* Death: Ingestion of large amounts of salt in a short time (about 1 g per kg of body weight) can be fatal. Deaths have also resulted from attempted use of salt solutions as emetics, forced salt intake and accidental confusion of salt with sugar in child food.
The risk for disease due to insufficient or excessive salt intake varies because of biochemical individuality. Some have asserted that while the risks of consuming too much salt are real, the risks have been exaggerated for most people, or that the studies done on the consumption of salt can be interpreted in many different ways
In the United Kingdom, the Scientific Advisory Committee on Nutrition (SACN) recommended in 2003 that, for a typical adult, the Reference Nutrient Intake (RNI) is 4 g salt per day (1.6 g or 70 mmol sodium). However, average adult intake is two and a half times the Reference Nutrient Intake for sodium. SACN states, "The target salt intakes set for adults and children do not represent ideal or optimum consumption levels, but achievable population goals."
The Food Safety Authority of Ireland endorses the UK targets. Health Canada recommends an adequate Intake (AI) and an Upper Limit (UL) in terms of sodium, as does. Health Canada recommends an AI of 1200-1500 mg and an UL of 2200-2300 mg per day for persons aged 9 years or more. The NHMRC in Australia was not able to define a recommended dietary intake (RDI). It defines an AI for adults of 460-920 mg/day and an UL of 2300 mg/day. In the United States, the Food and Drug Administration itself does not make a recommendation, but refers readers to Dietary Guidelines for Americans 2010. These suggest that US citizens should consume less than 2,300 milligrams per day. People over 51 years of age, who are black, or who have hypertension, diabetes, or chronic kidney disease (regardless of age) should limit intake to 1,500 milligrams per day.
Small amounts of sodium are essential for health. All body fluids contain sodium, including blood, and it has an important function in maintaining fluid balance within the body. In this context, it is important that the body is able to regulate the level of sodium in the blood. Sodium is also necessary in generating electrical impulses in nerve and muscle and in generating gradients across cells to enable uptake of nutrients. As excess salt in the diet is readily absorbed control of sodium in the blood is achieved by excretion through the kidneys into the urine.
Salt requirements are closely related to water requirements, and in extreme circumstances too low an intake results in muscular cramps. This can occur after strenuous exercise or in hot climates. People suffering from kidney disease and very young infants cannot tolerate high sodium intakes because their kidneys cannot excrete the excess. For this reason, salt should never be added to any foods for young babies.
Sodium is present in additives such as monosodium glutamate (a flavor enhancer), sodium saccharin (a sweetener), sodium nitrite (a preservative), sodium ascorbate (an antioxidant) and sodium bicarbonate (baking soda), and in some medicinal products e.g. antacids. But, most sodium in the diet comes from salt. Sodium and chloride levels are comparatively low in all foods which have not been processed. However, salt has been used as a preservative and a flavoring agent for centuries. It is also used as a color developer, binder, texturiser and fermentation control agent (e.g. in bread making). For these reasons, it is added to foods such as ham, sausages, bacon and other meat products, smoked fish and meats, canned vegetables, most butter, margarine and spreads, cheese, bread, savory snack foods and some breakfast cereals.
Too much sodium in the diet has been associated with an increased risk of developing stomach cancer and adverse effects on the kidney if there is some underlying abnormality. It is also one of the dietary and lifestyle factors that have been linked to high blood pressure or hypertension. Whilst hypertension is often symptom less, it increases the risk of conditions such as heart disease and stroke. The Dietary Approaches to Stop Hypertension (DASH) Study has shown the most effective diet to prevent or treat high blood pressure to be one that is low in fat and sodium and includes low fat dairy products (a source of calcium), as well as fruit and vegetables (a source of potassium). This emphasizes the importance of improving the whole diet rather than focusing on any individual nutrient. Other lifestyle factors, such as being physically active, not smoking and maintaining a healthy body weight are also important in preventing hypertension.