Introduction to Nutrition Minerals
Calcium Over 99% of the adult body’s 1000-1200g
Table 1: Adequate Intakes (AIs) for Calcium [1]
Age
Male
Female
Pregnant
Lactating
Birth to 6 months
210 mg
210 mg
7-12 months
270 mg
270 mg
1-3 years
500 mg
500 mg
4-8 years
800 mg
800 mg
9-13 years
1,300 mg
1,300 mg
14-18 years
1,300 mg
1,300 mg
1,300 mg
1,300 mg
19-50 years
1,000 mg
1,000 mg
1,000 mg
1,000 mg
50+ years
1,200 mg
1,200 mg
calcium is in the bones and teeth,
? The rest, less than 1%, plays an essential part in the functioning of many diverse vital activities such as the clotting of blood, absorption of vitamin B 12, hormone secretion etc..
? The calcium in the blood is kept within a very narrow concentration range - using the bones as a source of calcium when needed and as a store for calcium when the blood concentration is rising.
? This careful control is achieved mainly by means of several hormones.
- Parathormone, secreted from the parathyroid glands in the neck, increases calcium in blood.
- Calcitonin, secreted by thyroid gland, decreases calcium in blood.
- The effect of these hormones on bone is affected by vitamin D, which is itself a hormone.
? At birth, the bones are still soft but there is rapid calcification during infancy. At age 6 months, the infant lays down in the bones almost as much calcium per day as does a 10-year-old (about 150mg).
? At around 15 years there is a peak accumulation of about 400mg of calcium per day, which then declines to around 50mg per day at 20 years.
? Peak bone mass is not achieved until 30 years of age.
? At 40 years a steady decline in bone calcium starts - by about 75 years the skeleton has only about 70% of the calcium it had at its peak.
? This loss of calcium is more marked in women than in men, especially after the menopause.
? Bone fully calcified is made up of 50% calcium phosphate, 20% protein, and the rest is made up fo around 25% water plus 5% fat.
? In poor dietary conditions: may be under-development of the skeleton because of protein lack and possibly also inadequate energy intake, such subjects being shorter and lighter than they would have been on a good diet.
? The calcium in the skeleton, unlike that in the teeth, is constantly being renewed.
- In an adult this calcium renewal amounts to about 500mg per day.
- All the calcium in the skeleton is renewed about once in seven years.
- The turnover is very much faster in young children, taking as little as one year to renew all the calcium.
? The amount of calcium laid down is greatly increased by exercise, especially when lifting and carrying are involved.
? Prolonged bed rest causes a rapid loss of bone calcium.
Absorption of calcium
? Dietary calcium is absorbed into the blood mainly by the first 30cm of the small intestine, where the lining cells are specially adapted for this purpose.
? The absorption of calcium by the normal adult is not particularly efficient - 30-60% - when the intake is about 400-1000mg calcium per day.
? In actively growing children, in contrast, the absorption rate can be as much as 75% of intake.
? Vitamin D affects efficiency of calcium absorption and it increases its uptake.
? Oher dietary constituents reduce the uptake of calcium e.g. phytate and oxalate (cereals, oats, wholemeal bread, rice, pasta, spinach, soybean).
Sources of calcium
? Milk is rich in calcium and the mineral is very well absorbed from dairy products.
- One pint (0.6 litres) of milk contains about 700mg of calcium.
- 100g of hard cheese contains 700mg of calcium.
- The removal of the fat from milk leaves behind all the calcium so that semi-skimmed and skimmed milk are just as calcium-rich as is full-fat milk.
Calcium content of common foods
Very high (more than 500mg/100g portion)
Hard cheese. milk
High (200-300mg/100g portion)
Almonds, hazelnuts, soybeans
Medium (50-200mg/100g portion)
Beans, bread, broccoli. Cottage cheese, lentils, prunes, raisins, dried dates
Low (less than 50mg/100g portion)
Barley, brussels sprouts, cabbage, carrots, cashews, cauliflower, poultry, rice, tomatoes
? Although soft water has almost no calcium, fresh hard water may contain sufficient to provide about 20% of the daily need; boiling hard water causes almost all the calcium to be precipitated as an insoluble material.
Requirements of calcium
? The daily calcium intakes recommended in different countries vary considerably, especially since about 1990, when values were generally greatly increased.
? Most of the changes in recommended intake have been based on recent research into osteoporosis and the realisation that the best preventive measure is to have maximum bone calcification in childhood and in the early adult years.
? Many Western diets have a liberal amount of phosphate, which causes an increased loss of calcium in the urine. Much of this phosphate is derived from protein, so that a diet rich in protein increases the need for calcium.
Osteoporosis
? Condition in which bones become brittle, but not soft, because calcium salts are lost from their substance. The bones do not shrink but remain their original size.
? Skeleton achieves its peak mass at around 30 years of age and remains stable for about 10 years – it then begins to lose bone mass because the bone lost is not completely replaced.
? This age-related bone loss occurs in both sexes but is about four times greater in the female after the menopause and reflects the falling level of the hormone oestrogen.
? Unlike men, who do not usually have sufficient loss of bone calcium to cause inconvenience, women by the age of 70 years will have lost an average of about 50% of their bone mass.
? About a quarter of all women of that age will have had at least one bone fracture (parts affected are the vertebrae, top end of the femur, the wrist).
? Small-boned women who have had a sedentary life are most at risk, especially if they have had repeated spells of dieting. The bones heal slowly and less well and immobility during treatment makes bone loss worse.
? Any condition which reduces oestrogen levels in young women will help to produce osteoporosis, so that anorexia nervosa and excessive exercise, such as marathon running, which lead to amenorrhoea, are two well-known causes.
? Prevention is better than cure:
- Some types of exercise, are very valuable in preventing bone loss and they are those which involve lifting and carrying, the load-bearing bones laying down extra calcium as a result of the strain placed upon them.
- Treatment of osteoporosis never brings the bones back to their optimum state even though some benefit can often be obtained.
- Best prevention is during childhood and young womanhood by a diet rich in calcium, portein and the vitamins, especially vitamin D produced by sunlight on the skin or taken in the diet.
- The daily calcium intake should be about 1500mg per day. This can be achieved by taking 600ml (one pint) of skimmed milk plus 100g of low-fat hard cheese.
- Some women seem to be more at risk of osteoporosis because peak bone mass is primarily genetically determined: girls with a family history of osteoporosis should take preventive measures early and seriously.
- There is evidence that cigarette smoking and alcohol may make osteoporosis worse.
Phosphate
? About 1% of the adult body is phosphorus, of which 85-90% is in the bones and teeth, about 5% in the muscles, and the rest in the remaining tissues.
? It is essential in all reactions releasing energy. It is involved in the release of energy from fat, protein, and carbohydrates during metabolism and in the formation of genetic material, cell membranes and many enzymes.
? The intake of phosphate by the adult should be about equal to that of calcium.
Sources of foods
? Phosphate is found in virtually all foods and is high in those rich in protein such as meat, poultry, fish, eggs and cereals.
Iron
? About 2/3 of the iron in an adult is carried in the red blood cells in a red-coloured molecule called haemoglobin.
? This substance carries oxygen from the lungs to the tissues, carries carbon dioxide from the tissues to the lungs. The haemoglobin is inside the red cells to prevent it being excreted by the kidneys.
? The rest of the body’s iron is in enzymes, in co-factors, in muscle myoglobin, and in storage as ferritin and haemosiderin mainly in the liver, the spleen and the bone marrow.
? About 20-25mg of iron is needed each day for the synthesis of new haemoglobin but only 1-2mg of this is newly absorbed dietary iron, the rest being iron which has been previously used and recycled. The body is exceptionally efficient in its iron usage.
? Iron is lost from the body only by the rubbing off of skin and hair and by bleeding.
? Under normal conditions, the adult man and the non-pregnant non-menstruating woman lose only about 1 mg of iron a day.
? As the store in health is 500mg-1500mg it would normally take several years for the store to be depleted on a diet deficient in iron.
Sources of Iron
? Most men get enough dietary iron but many women, especially if menstruating or pregnant, do not.
Iron content of common foods:
High (more than 6mg/100g portion)
Kidney beans, lentils, soybean
Medium (4-6mg/100g portion)
Almonds, cashews, dried figs, hazelnuts, prunes, wholegrain rice
Low (2-4mg/100g portion)
Bacon, barley, beef, brazil nuts, chicken, chocolate, egg, ham, veal, peas
Very low (less than 2mg/100g portion)
Cheese, fish, cornflakes, fruit, milk
? The iron in some foods is only poorly, or very poorly, absorbed into the blood by the intestine.
- Iron in animal products is well absorbed while plant iron is not. An exception to this is egg, from which only about 2% of the iron can be used because of the high phosphate content in egg.
- In contrast, about 20% of the iron in steak, pork, lamb, poultry, and fish enters the blood.
- An example of a plant with a good iron content which is not very useful is spinach, because the large amount of oxalic acid in spinach prevents much of the iron from being absorbed.
- 20% of the iron in soybean can be absorbed into the blood, which is exceptional for a plant food.
? For all foods, the presence of vitamin C aids the absorption of iron so that vitamin C-rich foods, such as orange juice, is best taken with meals.
? Iron absorption is much more efficient in the young than in the adult and it increases when there is a need for iron (in certain types of anaemia and during pregnancy). Iron absorption can be inhibited by excessive consumption of coffee.
? Iron overdose can cause severe illness.
? Vegetarian diet
- may contain what seems to be an adequate amount of iron but if the dietary fibre in the food is very high the amount of iron absorbed into the blood may be too low.
- inclusion of eggs and milk products in a vegetarian diet does not help because the iron of eggs is very poorly absorbed and milk only have a small amount of iron.
- many vegetarian women of child-bearing age have a low haemoglobin concentration in their blood. A breakfast cereal well-fortified with iron should be taken each day.
Daily needs of Iron
Infants
5-15mg
Children
5-10mg
Adolescent boys and girls
10-20mg, 10-25mg
Adult males
10-15mg
Non-menstruating women
5-10mg
Menstruating women
10-25mg
Pregnancy
15-35mg
Iron in Infancy
? Healthy newborn babies have an iron reserve in the liver which satisfies their needs for 3-6 months – this is essential because milk contains little iron and for the first three months the immature intestine can absorb only very small amounts of the metal.
? Unmodified cows’ milk should not be fed to infants as a drink because it can cause bleeding into the intestine.
Iron deficiency
? Iron deficiency is one of the commonest nutritional deficiencies, not only in poor countries but also in the richer ones. It affects mostly women and children.
? Women who have had repeated pregnancies and women with heavy periods are often permanently mildly anaemic and so is anybody who has chronic bleeding.
? The store of iron in a normally well-fed person is large, so it can take several years for an iron-deficiency anaemia to develop when changing to an iron-poor diet.
? The severity of the symptoms in anaemia vary considerably from person to person. They may include weakness, tiredness, loss of appetite, breathlessness on exercise, palpitations, sore tongue and swollen ankles.
Sodium, potassium and chloride
Sodium
? There are about 100g of sodium in the adult:
- 10% being inside the cells
- 50% in the fluids outside the cells
- 40% in the bones, which act as a reserve from which sodium can be released to keep the blood level constant.
? Sodium plays an essential part in controlling osmotic pressure, in the conduction of nerve impulses, in muscle contraction and in the transport of substances into and out of cells.
? Some popular foods often high in salt:
- bacon, baked beans, canned meats, canned soups, hard cheese, corned beef, cornflakes, cottage cheese, crisps, fish fingers, ham, kippers, olives, salted peanuts, pizza, sausages, smoked haddock, tomato ketchup.
? For some foods, salt is added for its taste, while for other it is added as a help in preservation.
? The taste for salt is acquired during infancy, when food seasoned with salt is fed. Infants on weaning do not discriminate between salted and unsalted food but they gradually acquire a liking for salt which is difficult to break.
? The taste of such food can be improved by the addition of spices, which generally contain very little sodium. cooked in plain water.
? Sodium can be lost in considerable amounts in severe vomiting, diarrhoea, renal failure, adrenal gland failure, excessive use of diuretcs, chronic wasting diseases, extensive burns, major surgery and excessive sweating.
? The results of a severely lowered blood sodium concentration are nausea, anorexia, muscle weakness and spasm, headache, confusion, coma and death.
High blood pressure (hypertension)
? In some people, high blood pressure is lowered by a reduction in sodium intake.
? The giving-up of salt at the table with only moderate use of salt in cooking sometimes induces a worthwhile fall in the blood pressure and may be preferable to the taking anti-hypertensive drugs.
Potassium
? Potassium is an essential component inside every cell, where it is involved in many vital reactions. It is important in sending nerve impulses and in maintaining normal fluid balance. It influences muscle activity, especially cardiac muscle.
? The ordinary diet provides more potassium than is needed each day and the excess absorbed is normally excreted in the urine.
? Very good sources are oranges, bananas, meat, cauliflower, potatoes, Brussels sprouts, broccoli, and tomatoes.
? Excess: very unlikely to occur unless there is kidney failure, adrenal gland disease or very severe damage to tissues causing them to release their potassium into the blood. The symptoms are muscle weakness, paralysis and cardiac arrest.
Chloride
? Is it abundant in virtually all normal foods and dietary lack is unknown.
? Chloride can be lost from the body to cause severe symptoms during prolonged profuse sweating, repeated vomiting and intractable diarrhoea.
? The chloride ion, together with sodium, plays an essential role in maintaining fluid balance in the body and in the absence of enough chloride there is lose of body water via the kidneys, resulting eventually in collapse and death because of inadequate functioning of the cardiovascular system.
Iodine
? Iodine is essential for the production of the hormones of the thyroid gland, which lies alongside the larynx in the front of the neck.
? In the absence of an adequate iodine intake, the thyroid gland enlarges to produce a smooth, painless, rounded lump, easily seen moving up and down during swallowing.
? Dietary iodine is easily and almost completely absorbed but there is no body store of the element, so that a regular frequent intake is necessary.
? The thyroid hormones increase the rate of metabolism of all cells, sometimes by as much as 30%.
Sources
? The amount of iodine in a food depends on the place in which the food was grown. Where the soil is rich in iodine, plants have a high iodine content and the tissues of animals eating such plants also become iodine-rich.
? The use of iodized salt, containing about 2mg of potassium iodide per 100g of salt, is a simple and very useful nutritional measure and costs very little. A person eating 2g of such a fortified salt each day would get 30ug iodine, a very valuable addition to the daily iodine intake.
Fluoride
? Fluoride is particularly important because it is the only nutrient to substantially reduce dental caries. The fluoride makes the enamel of the teeth more resistant to bacterial acid and it reduces the amount of bacterial acid produced.
? Adding fluoride to drinking water can reduce dental caries by up to 70%.
Sources
? The main source of dietary fluoride is drinking water.
? Tea is a rich source.
? Seafood in general has a good fluoride level with mackerel high in the mineral.
Fluoride supplements
? Supplements are supplied either as drops, which are added to drinks, or as tablets, which should be allowed to dissolve in the mouth and not swallowed whole.
? As soon as teeth erupt they should be cleaned with a fluoride toothpaste provided the child learns not to swallow the toothpaste.
Toxicity
When drinking water has more fluoride than about 2.5 parts per million the tooth enamel may become mottled although the teeth usually remain sound and highly resistant to caries.
When the levels reach about 15 parts per million, fluoride poisoning occurs.
1. Selenium
? Selenium is most abundant in plants grown in selenium-rich soil, as in the US, whereas most European-grown plants are poor in selenium unless it is added to the soil which is now done in most countries.
? Good sources of selenium are wholegrain cereals, fish and meat, if they come from a selenium-rich environment. Brazil nuts are very rich in selenium. Milk and milk products are low in selenium unless the element is added to the animals food.
? Selenium prevents oxidation of fat within the cells and in the cell membranes, they reduce the occurrence of atherosclerosis, protect DNA and inactivate carcinogens. It is also involved in the reactions which release energy in cells.
Selenium deficiency
? An inadequate amount of selenium in the diet may produce degeneration of the cardiac muscle and general skeletal muscle pain. The heart damage can be fatal.
? Selenium deficiency in men is believed to cause low fertility.
Toxicity of Selenium
? Increasing the normal dietary intake of selenium by an extra 150ug or more, by taking supplements, seems to have caused nausea, vomiting, nail defects and hair loss.
Zinc
? Zinc is needed for many cellular enzymes involved in the metabolism of carbohydrate, protein and fat and for the synthesis of protein and DNA.
? There are high concentrations of it in the male reproductive system and also in parts of the eye.
? Almost all the zinc in the body is in use a regular daily intake is needed, especially during growth and tissue healing.
Sources of Zinc
? Rich sources of zinc are meat, poultry, liver, wholegrain cereals, pulses, herring and shellfish.
? Vegetables and fruit are poor in zinc and their phytate content diminishes zinc absorption into the blood, as does a high calcium intake.
Requirements of Zinc
? Zinc is relatively non-toxic but massive doses can be harmful. Long-term dosage with moderate but unneeded dose should be avoided because the effect of such a regime is unknown.
Zinc deficiency
? Zinc-deficient children tend to have more infections, grow less well and may have diarrhoea.
? In adults, zinc deficiency produces loss of appetite, diarrhoea, diminished taste, anaemia, skin erosions, and scalp hair loss. Zinc lack is made worse by alcoholism, liver disease, kidney disease, rheumatoid arthritis and surgical operations.
For further information visit www.mehfa.eu
A Sports, Leisure and Tourism lecturer currently President of the Malta Exercise Health and Fitness Association and teaching Fitness instructors and Personal trainers. Member on the EU affairs board of the European Health and Fitness Association.
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