Minerals: Iron and Sodium

This lesson covers iron and sodium, two minerals with very different roles and concerns, as required by AQA GCSE Food Preparation and Nutrition (8585), specification section 3.2.2. Iron deficiency is the most common nutritional deficiency worldwide, while excessive sodium intake is a major public health concern in the UK. Both are frequently examined.

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Iron

Iron is a trace mineral (trace element) — it is needed in small amounts, but it is absolutely essential for life. The body of an average adult contains approximately 4 grams of iron, most of which is found in the blood.

Functions of Iron

Function	Detail
Haemoglobin production	Iron is a key component of haemoglobin, the protein in red blood cells that carries oxygen from the lungs to every cell in the body. Without iron, haemoglobin cannot be formed, and oxygen delivery is impaired.
Myoglobin	Iron is also part of myoglobin, a protein that stores oxygen in muscle cells for use during physical activity.
Energy metabolism	Iron is involved in enzyme systems that release energy from food.
Immune function	Iron supports the normal function of the immune system.
Cognitive function	Adequate iron is important for concentration, memory, and mental performance, particularly in children and adolescents.

Types of Dietary Iron

There are two forms of iron in food, and this distinction is very important:

Type	Source	Absorption
Haem iron	Found only in animal products — red meat, liver, kidney, poultry, fish	Well absorbed (15–35% absorption rate). Not significantly affected by other dietary factors.
Non-haem iron	Found in plant foods and also in animal products — dark green leafy vegetables, pulses, fortified cereals, dried fruit, wholegrain bread	Less well absorbed (2–20% absorption rate). Absorption is affected by other dietary factors.

flowchart TD
    A["Dietary Iron"] --> B["Haem Iron<br/>(animal sources)"]
    A --> C["Non-Haem Iron<br/>(plant sources)"]
    B --> D["Well absorbed<br/>(15-35%)"]
    C --> E["Less well absorbed<br/>(2-20%)"]
    F["Vitamin C"] -->|"enhances<br/>absorption"| E
    G["Tannins in tea<br/>Phytates in cereals"] -->|"inhibit<br/>absorption"| E

    style B fill:#c0392b,color:#fff
    style C fill:#27ae60,color:#fff
    style F fill:#f1c40f,color:#000
    style G fill:#e74c3c,color:#fff

Factors Affecting Iron Absorption

Factor	Effect on Iron Absorption
Vitamin C	Enhances absorption of non-haem iron. Eating Vitamin C-rich foods with iron-rich foods significantly improves uptake.
Haem iron	Haem iron is inherently better absorbed than non-haem iron.
Tannins (in tea and coffee)	Inhibit non-haem iron absorption. Drinking tea with meals reduces iron uptake.
Phytates (in wholegrain cereals)	Inhibit non-haem iron absorption by binding to iron in the gut.
Calcium	High calcium intake at the same meal can reduce iron absorption.
Oxalates (in spinach)	Inhibit iron absorption — spinach contains iron but also oxalic acid, which reduces how much iron is actually absorbed.

Exam Tip: The Vitamin C/iron absorption link and the tannin/iron absorption link are among the most commonly tested facts. Always mention Vitamin C as a way to enhance non-haem iron absorption and tea/tannins as an inhibitor.

Sources of Iron

Source Type	Examples
Red meat	Beef, lamb, pork (haem iron — well absorbed)
Offal	Liver, kidney (very rich in haem iron)
Poultry and fish	Chicken, turkey, tuna, sardines (haem iron)
Dark green leafy vegetables	Spinach, kale, broccoli, watercress (non-haem iron)
Pulses	Lentils, chickpeas, kidney beans, baked beans (non-haem iron)
Fortified cereals	Many breakfast cereals are fortified with iron; UK flour is fortified by law (non-haem iron)
Dried fruit	Apricots, raisins, figs (non-haem iron)
Eggs	(non-haem iron)
Wholegrain bread	(non-haem iron)

Deficiency of Iron

Iron deficiency is the most common nutritional deficiency in the world and is also common in the UK, particularly among certain groups.

Iron-deficiency anaemia occurs when the body does not have enough iron to produce adequate haemoglobin. Red blood cells become small and pale (microcytic, hypochromic) and cannot carry sufficient oxygen.

Symptom	Explanation
Tiredness and fatigue	Reduced oxygen delivery to cells means less energy is produced.
Pale skin and pale inner eyelids	Less haemoglobin gives blood a paler colour.
Shortness of breath	The body tries to compensate for reduced oxygen by breathing faster.
Dizziness and headaches	Reduced oxygen to the brain.
Cold hands and feet	Poor oxygen delivery to extremities.
Brittle nails	Nails may become thin, flat, or spoon-shaped (koilonychia).
Poor concentration	Especially noticeable in school-age children.
Weakened immune system	Increased susceptibility to infections.

Groups at Risk of Iron Deficiency

Group	Reason
Teenage girls and women of childbearing age	Iron is lost through menstruation each month. Teenage girls who also have a poor diet are especially at risk.
Pregnant women	Blood volume increases during pregnancy, requiring more iron. The developing baby also needs iron.
Vegetarians and vegans	No haem iron in the diet; non-haem iron is less well absorbed. Must rely on plant sources plus Vitamin C to enhance absorption.
Young children	Rapid growth increases iron demand. Fussy eating can lead to inadequate intake.
Athletes	Increased iron loss through sweat and higher demand for oxygen transport.
Older adults	Reduced appetite and dietary variety can lead to low iron intake.

Exam Tip: When advising a vegetarian on how to improve iron intake, suggest: (1) eating iron-rich plant foods (dark green leafy veg, pulses, fortified cereals), (2) consuming Vitamin C with meals to enhance absorption, and (3) avoiding tea with meals as tannins inhibit absorption.

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Sodium

Sodium is a macro mineral found mainly as sodium chloride (table salt) in the diet. While sodium is essential for life, the major concern in the UK is excess intake rather than deficiency.

Functions of Sodium