Title: Minerals - The Major Elements

Key words: enzyme systems, muscle contraction, nerve impulses, blood clotting, calcium, iron, magnesium, phosphorus, potassium, dietary sources, optimal intake, functions, deficiency, excess,

Date: June 2000

Category: Micronutrients

Type: Article

Author: DJE Candlish

 

Minerals - The Major Elements

 

 

Introduction

Inorganic minerals are nutrients needed for the development of structural components of both hard and soft body tissues. They are also required for the normal functioning of enzyme systems, for muscle contraction, nerve impulse transmission and blood clotting. As the body cannot produce mineral nutrients, they must be supplied by the diet or by supplementation. There are two main classes of dietary mineral:

 

 

 

Category: Major Elements

Nutrient: Calcium

Dietary Sources:

The best dietary sources of calcium include milk, cheese, sardines and green vegetables. Although the body can not produce calcium itself, it can be stored in bones and reabsorbed when needed.

Optimal Intake:

Age

0–12 months

1–3 years

4–6 years

7–10 years

11–18 years (m)

11–18 years (f)

19+ years

Lactation

intake (m g/day)

525

350

450

550

1000

800

700

1250

Women who are pregnant or lactating need a higher intake, as their growing child needs calcium to form teeth and bones.

Post-menopausal women may benefit from calcium supplementation, as this may help to retain their bone density and strength.

A vegan diet is unlikely to supply the need for calcium and supplementation may be needed.

Antacids can interfere with calcium absorption, so people who take them regularly are at risk of calcium deficiency.

Functions:

Calcium is needed for healthy bones, teeth and nails (a 70kg adult contains around 1200g of calcium, mostly in the skeleton).

Calcium is involved in a wide range of body processes, including blood clotting, transmission of nerve impulses and muscle contraction.

Effects of Deficiency:

Calcium deficiency causes rickets and stunted growth in children, osteoporosis in menopausal women and the elderly and an increased risk of fractured bones, particularly in the elderly.

 

Effects of Excess:

A high calcium intake is not associated with harmful effects, as the body excretes any that is excess to its needs.

Additional Information

 

 

References/Further Reading:

 

 

Category: Major Elements

Nutrient: Iron

Dietary Sources:

Good dietary sources of iron include liver and red meat, poultry, wholegrain cereals and green vegetables.

Dietary iron exists in two forms: nonhaem (inorganic) and haem.

The two forms are absorbed by different mechanisms.

Iron absorption is influenced by the dietary iron content, its bioavailability, the amount of iron already stored in the body and the rate of erythrocyte (red blood cell) production. It also depends upon the types of food eaten and the interaction between the food and regulatory mechanisms in the intestinal mucosa which reflect the body's physiological need for iron ( See Table 2 ).

 

Optimal Intake:

Age

0–3 months

4–6 months

7–12 months

1–3 years

4–6 years

7–10 years

11–18 years (m)

11–50 years (f)

19–50 years (m)

50+ years

Intake (m g/day)

1,700

4,300

7,800

6,900

6,100

8,700

11,300

14,800

8,700

8,700

Functions:Iron is used to form haemoglobin, the substance in red blood cells that carries oxygen around the body to where it can be used by the tissues. Haemoglobin is the major iron-containing protein in the body. It is formed in the bone marrow and Iron is also used to form myoglobin, which provides oxygen specifically to muscle tissue during activity. Most body iron is stored in the form of two compounds - ferritin and haemosiderin. These are mainly present in the liver, reticuloendothelial system (RES) and bone marrow. The iron bound to ferritin is more readily mobilised than from haemosiderin.Iron is involved in the processes by which energy is released within cells. It also contributes to immune defences and growth in childhood.

Effects of Deficiency:

Loss of blood either through haemorrhage or menstruation can put the body into a negative iron balance. This eventually causes anaemia (pale skin, tiredness, depression). A simple blood test to measure haemoglobin levels can confirm the diagnosis of anaemia. Other effects include stunted growth and impaired mental function in children and pruritus (itching all over the body) in both adults and children.

Effects of Excess:

Although iron supplements are generally safe, care should be taken as some people can not tolerate large amounts of the mineral. Vitamin C helps iron to be absorbed better.

Iron can irritate the stomach, causing nausea, vomiting, diarrhoea and constipation. Overdoses with extremely large amounts of iron can cause hypotension, coma and even death.

Additional Information

Iron absorption is influenced by the dietary content, bioavailability , amount of storage iron and the rate of erythrocyte production. The entry of iron into the body is regulated by the mucosal cells of the gastrointestinal tract. The percentage of non-haem iron absorbed is increased if the iron stores are low, after haemorrhage or pregnancy, for example. Men have higher iron stores than women and childen, who are able to absorb a higher percentage of iron from the diet.

Iron is transported around the body in the form of a complex formed from iron and transferrin, a plasma transport protein. Cell membrane receptors bind the transferrin-iron complex and carry it into the cell. Tissue affinity in different tissues varies. Erythroid precursors, the placenta and liver have a high iron uptake. In an iron-rich environment the number of receptors decreases. The regulator genes that control this are located on chromosome 3.

Sources of Iron losss are summarised in Table 2. Haemoglobin represents the largest iron containing protein in the body and loss of blood either through haemorrhage or menstruation can put the body into a negative balance and cause anaemia. Myoglobin, present in muscle, has a high affinity for oxygen. Training increases myoglobin levels and reduces lactic acid build up during exercise. The cytochrome system is critical to respiration and to energy metabolism in the mitochondria. Non haem iron-containing enzymes, such as NADH and Succinate dehydrogenase, are also involved in energy metabolism.

 

 

 

References/Further Reading:

1. BENDER, D.A. 1997; Introduction to Nutrition and Metabolism, Taylor & Francis ISBN 0-7484-0781-2

2. WORLD HEALTH ORGANISATION 1996; Trace Elements in Human Nutrition and Health .- WHO Geneva. ISBN 92-4-156173-4

3. ZIEGLER, E. E., FILER,L.J. 1996; Present Knowledge in Nutrition

p.277-289- International Life Sciences Institute. ISBN 0-944398-72-3

 

Table 1. Iron Distribution in the Body

Haemoglobin

2-3 gms

Muscle myoglobin

0.5 gms

Mitochondrial cytochromes and enzymes eg Succinate Dehydrogenase.

0.1 gms

Storage Iron

1.5 gms

Total Iron

4-5 gms

Table 2. Iron uptake and distribution.

 

 

Iron Intake

 

Absorption

Mucosal

Transferrin

 

Internal Metabolic Pool

 

Iron Stores

Tissue ferritins

Haemosiderin

             

RDA mg/day

Children 5- 10

Male 10-12

Female 10-15

Pregnancy 30

     

Iron losses in m g/day

Genitourinary 100

Skin 200

Gut 300 -600

Females (menstrual bleeding) 1-2 mg/day

   

 

 

Category: Major Elements

Nutrient: Magnesium

Dietary Sources:

Good dietary sources of magnesium include nuts, wholemeal bread, hard water, dairy products, fish and vegetables

Optimal Intake:

Age

0–3 months

4–6 months

7–9 months

10–12 months

1–3 years

4–6 years

7–10 years

11–14 years

15–18 years

19+ years (m)

19+ years (f)

Lactation

intake (mg/day)

55

60

75

80

85

120

200

280

300

300

270

320

 

Functions:

Magnesium is involved in a wide range of body functions. It is essential for growth and helping to keep cells and tissues healthy. It is also needed for the normal functioning of nerve, muscle and bone cells.

Effects of Deficiency:

These include nervous problems, such as irritability and stress, muscle tremors and cramps, irregular heartbeat (arrhythmia) and ‘pins and needles’ sensations.

Effects of Excess:

 

Additional Information

Magnesium supplements are usually free from harmful effects, although people with kidney disorders should avoid taking them.

 

References/Further Reading:

 

 

Category: Major Elements

Nutrient: Phosphorus

Dietary Sources:

Phosphorus is found in milk, meat, eggs, fish, fruit and wholegrain cereals.

Optimal Intake:

 

Functions:

Phosphorus is the second most important mineral in bones and teeth (85% of the 750g-1kg in our bodies). It is involved in the production of energy within cells, often in combination with B vitamins.

Phosphorus also plays an important role in cell membranes and genetic material.

Effects of Deficiency:

Phosphorus deficiency is very rare, but symptoms can include muscle disorders and weakness, respiratory or cardiac failure. For post-menopausal women, phosphorus supplements may help to reduce the risk of osteoporosis.

Effects of Excess:

There are few side effects associated with phosphorus excess, although diarrhoea and nausea can occur.

Additional Information

 

 

References/Further Reading:

 

 

 

Category: Major Elements

Nutrient: Potassium

Dietary Sources:

The best dietary sources of potassium include fruit and vegetables, potatoes and wholemeal bread.

Optimal Intake:

Age

0–3 months

4–6 months

7–12 months

1–3 years

4–6 years

7–10 years

11–14 years

15+ years

intake (mg/day)

800

850

700

800

1,100

2,000

3,100

3,500

Functions:

The presence of iron helps maintain the body’s fluid balance. It is essential for the normal functioning of nerves and muscles and is also involved in the regulation of blood pressure.

Effects of Deficiency:

These include weakness, listlessness and drowsiness, loss of appetite, nausea and thirst.

Effects of Excess:

High potassium intake should be avoided by people with kidney disorders, as they can cause a number of problems, including heart failure.

Additional Information

People taking diuretics and antibiotics may benefit from potassium supplementation, as these drugs can increase the excretion of potassium. Athletes and people in strenuous professions also lose a lot of potassium in their sweat.

 

References/Further Reading: