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

Function	Detail
Fluid balance	Sodium helps regulate the balance of water inside and outside cells (osmotic balance). This is critical for maintaining blood volume and blood pressure.
Nerve function	Sodium ions are essential for transmitting nerve impulses (electrical signals) along nerve cells.
Muscle contraction	Sodium works with potassium to enable muscle contraction and relaxation.
Nutrient absorption	Sodium helps the small intestine absorb certain nutrients, including glucose and amino acids.

Sources of Sodium

The vast majority of sodium in the UK diet comes from processed and manufactured foods, not from salt added at the table or during cooking.

Source Type	Examples
Processed foods	Ready meals, crisps, savoury snacks, takeaway food, canned soups, processed meats (bacon, ham, sausages, salami)
Bread	One of the largest contributors to sodium intake in the UK due to the quantities consumed
Cheese	Particularly hard and processed cheese
Sauces and condiments	Soy sauce, ketchup, gravy granules, stock cubes
Breakfast cereals	Some contain significant amounts of salt
Salt added during cooking or at the table	Table salt, sea salt, rock salt
Natural sources	Small amounts are naturally present in most foods, including meat, fish, vegetables, and milk

Exam Tip: Approximately 75% of the sodium in the UK diet comes from processed and manufactured foods. Only about 10–15% is added during cooking or at the table. This is an important fact — it means that reducing processed food consumption is more effective than simply not adding salt at the table.

Recommended Intake

The UK government recommends that adults consume no more than 6 grams of salt per day (equivalent to about 2.4 grams of sodium). Current average intake in the UK is approximately 8 grams of salt per day — significantly above the recommended limit.

Age Group	Maximum Recommended Salt Intake
1–3 years	2 g/day
4–6 years	3 g/day
7–10 years	5 g/day
11 years and over	6 g/day
Adults	6 g/day

Health Risks of Excess Sodium

Excess sodium intake is a major public health concern because of its link to several serious conditions:

Condition	How Excess Sodium Contributes
High blood pressure (hypertension)	Excess sodium causes the body to retain water, increasing blood volume and putting extra pressure on blood vessel walls.
Coronary heart disease (CHD)	High blood pressure damages the walls of arteries, increasing the risk of fatty deposits (atherosclerosis), which can lead to heart attacks.
Stroke	High blood pressure increases the risk of blood vessels in the brain bursting or becoming blocked.
Kidney disease	The kidneys must work harder to excrete excess sodium, potentially causing long-term damage.
Stomach cancer	Some evidence links high salt intake to increased risk of stomach cancer.

flowchart TD
    A["Excess Sodium<br/>Intake"] --> B["Water Retention"]
    B --> C["Increased<br/>Blood Volume"]
    C --> D["High Blood<br/>Pressure"]
    D --> E["Coronary Heart<br/>Disease"]
    D --> F["Stroke"]
    D --> G["Kidney<br/>Disease"]

    style A fill:#c0392b,color:#fff
    style D fill:#e74c3c,color:#fff
    style E fill:#8e44ad,color:#fff
    style F fill:#8e44ad,color:#fff
    style G fill:#8e44ad,color:#fff

Strategies to Reduce Sodium Intake

Strategy	Detail
Read food labels	Check the traffic light labels and nutrition information panel. Choose products with green (low) salt indicators.
Reduce processed food	Eat fewer ready meals, takeaways, processed meats, and salty snacks.
Do not add salt at the table	Remove the salt shaker from the table.
Use less salt in cooking	Gradually reduce the amount of salt added to recipes.
Use herbs and spices	Flavour food with herbs, spices, lemon juice, garlic, and pepper instead of salt.
Choose low-salt alternatives	Select reduced-salt versions of sauces, stock cubes, and snacks.
Cook from scratch	Home-cooked meals generally contain less salt than processed equivalents.

Deficiency of Sodium

Sodium deficiency is extremely rare in the UK because salt is so prevalent in the diet. It can occur in cases of:

• Excessive sweating (e.g., extreme heat, prolonged intense exercise)
• Severe vomiting or diarrhoea
• Certain medical conditions