Unlike sodium and potassium, which are staple elements of the diet and present in ample amounts in all food of vegetable and animal origin, certain minerals are additional dietary requirements. Although most are present in the average diet, these minerals may not always be ingested in quantities sufficient to satisfy metabolic needs, especially during growth, stress, trauma, blood loss, and in some diseases.
Minerals are classified as major or trace depending on the body’s requirements. Major minerals include calcium, magnesium, chlorine, phosphorus, potassium, sulphur, sodium, and potassium.
Trace elements are other inorganic substances that appear in the body in minute amounts and are essential for good health. While little is known about their functions, knowledge comes primarily from observing how their absence, especially in animals, affects health.
Trace elements appear in sufficient amounts in most foods and include chromium, copper, fluorine, iodine, iron, selenium, and zinc.
Major Elements and Their Functions
1. Calcium: The body’s calcium requirements are generally met by consuming dairy products such as milk and cheese, along with dried legumes and vegetables. Approximately 90% of calcium is stored in bones, with a constant exchange occurring between blood, tissue, and bone.
Calcium intake is balanced by losses through urine and feces. Blood calcium levels, along with intestinal absorption, deposition, or mobilization from bones, are controlled by a complex interplay of vitamin D, parathyroid hormone, and calcitonin. Contrary to some beliefs, high intakes of protein and phosphorus do not lead to calcium loss, though excessive dietary fiber may hinder its absorption.
Calcium promotes bone rigidity, maintains the integrity of intracellular cement and cellular membranes, and regulates nervous excitability and muscle contraction. It may also protect against high blood pressure.
Increased calcium intake is necessary during periods of growth, pregnancy, and lactation. Diseases related to calcium metabolism include vitamin D deficiency, hypervitaminosis D, hypo- and hyper-parathyroidism, and some forms of renal disease.
Calcium depletion is challenging to recognize as 99% of the body’s calcium is stored in bones. A 1% reduction in bone calcium, though small, is significant (about 10–12 g). Osteoporosis, a calcium deficiency disease, results in reduced bone mass for a particular length or volume of bone, implying less mineral (calcium phosphate) and bone protein, which leads to reduced or impaired bone mobility.
Osteoporosis is common in postmenopausal women in industrial societies, causing bone pain and an increased risk of fractures. Lack of exercise and insufficient dietary calcium are potential causes.
2. Phosphorus: Phosphorus works in conjunction with calcium to form bones and teeth, maintain acid-base balance, and assist in haemostasis of calcium. It also plays a role in reactions involving carbohydrates, lipids, and proteins. The body’s chemical energy is stored in “high energy phosphate” compounds (ATP).
Although elemental phosphorus is extremely poisonous, dietary phosphorus ingested as phosphates (from foods like milk, cheese, yoghurt, fish, poultry, meats, and grains) is not toxic. Phosphorus deficiency results in general body weakness and calcium loss.
3. Magnesium: Magnesium is essential in human metabolism, playing a role in muscle and nerve activity, enzyme activation, and protein synthesis. It is also vital in maintaining the electrical potential in nerve and muscle cells. Foods rich in magnesium include whole grains and green leafy vegetables.
Magnesium deficiency leads to growth failure, behavioral problems, and occasional muscle spasms. It may also occur in alcoholism, diabetes mellitus, pancreatitis, and renal disease. Prolonged deficiency can cause changes in heart and skeletal muscles, while excessive retention of magnesium in renal disease results in muscle weakness and hypertension.
4. Sodium: Sodium is present in small but sufficient quantities in most natural foods, with liberal amounts found in salted prepared and cooked foods. Sodium helps maintain acid-base balance, body water balance, and nerve function.
Depletion occurs due to massive fluid loss, as seen in severe cases of diarrhea, vomiting, and excessive urination, resulting in weakness and exhaustion. Sodium depletion, often accompanied by chloride depletion, occurs in several disease states.
Deficiency causes muscle cramps, reduced appetite, and mental apathy, while excess sodium intake leads to oedema (fluid accumulation). Evidence suggests that excess dietary salt contributes to high blood pressure.
5. Potassium: Potassium, naturally occurring in foods such as bananas, leafy vegetables, potatoes, milk, and meats, is vital for maintaining acid-base and fluid balance, as well as nerve transmission. Potassium depletion, especially during diarrhea or the overuse of purgatives or diuretic drugs, causes weakness in voluntary muscles and stops intestinal peristalsis.
Under these conditions, the electrocardiograph shows low T waves. Potassium deficiency results in muscle cramps, mental confusion, loss of appetite, and irregular cardiac rhythm.
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Trace Elements and Their Importance
1. Iodine: Iodine is primarily found in salt-water fish, shellfish, dairy products, and vegetables. Its main function is in the synthesis of thyroxine and thyroid gland function. People living in coastal areas typically receive enough iodine from seafood, but inland regions may face iodine deficiency, leading to goitre.
Manufacturers often add iodine to table salt to prevent this. Iodine is crucial for the synthesis of thyroid hormones, and its absence can lead to enlarged thyroid glands, cretinism in infants, and other community-wide health issues. Iodised salt is effective for developed communities, but isolated communities may require injections of iodised oil.
2. Iron: Iron is an essential component of haemoglobin and some respiratory enzymes. It helps form haemoglobin, the red blood cell pigment that carries oxygen. Foods high in iron include meat, eggs, whole grains, wheat germ, legumes, and green vegetables. Iron requirements increase during growth, pregnancy, menstruation, and instances of blood loss.
A daily intake of 10 to 15 mg is adequate for most people. Iron deficiency, which leads to anemia, is common, especially in women. Each millilitre of blood contains 0.5 mg of iron, and blood loss depletes iron reserves, resulting in anemia.
3. Zinc: Zinc, found in lean meat, whole grains, dried beans, and seafood, acts as a cofactor for several enzymes and aids in wound healing. Zinc deficiency, often caused by stress or surgical operations, can result in loss of taste, retarded growth, delayed wound healing, and other health issues. Excessive zinc intake or inhalation can cause depression, vomiting, and headaches.
4. Fluorine: Fluorine, concentrated in dental enamel and bones, helps maintain bone structure and resist enamel erosion. Fluoride is found in tea and fish, and in some communities, drinking water is fluoridated. In places without fluoridation, fluoride tablets or treatments from dentists may be used. Deficiency can lead to osteoporosis and tooth decay.
Other Trace Minerals
Selenium, found in seafood, meat, and grains, prevents fat breakdown, and deficiency can cause various forms of anemia. Copper, found in meats and drinking water, aids red blood cell formation, with deficiency leading to anemia and impaired bone development. Chromium, present in legumes, cereals, and organ meats, assists glucose metabolism, with deficiency linked to adult-onset diabetes.
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The Importance of Dietary Fibre
Dietary fibre, or bulk, consists of plant materials that are not hydrolysed by human digestive enzymes. Although fibre has no direct nutritional value, it is essential for health. Over the past decades, dietary fibre’s role in preventing obesity, constipation, and several digestive disorders has become more widely recognized.
A high-fibre diet reduces the risk of heart disease by lowering blood cholesterol levels and preventing gallstone formation. Additionally, dietary fibre may reduce the risk of colon cancer by binding bile salts and carcinogenic compounds, preventing their interaction with intestinal cells.
Foods high in dietary fibre include fruits, vegetables, cereals, whole-grain bread, and products made from nuts and legumes. However, excessive fibre intake can inhibit the absorption of essential trace minerals during digestion.
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