Welcome to AS 1: Principles of Nutrition – Minerals
Welcome to your study notes for Minerals in CCEA AS 1 Nutrition and Food Science! While vitamins often get the spotlight, minerals are the unsung heroes of our bodies. From building rigid bones and teeth to conducting electrical nerve signals and carrying oxygen through your blood, minerals keep you alive and functioning every second of the day.
Don't worry if nutrition science feels overwhelming at first with all the chemical terms and absorption factors. We will break down every concept into straightforward, bite-sized steps so you can master your AS exam with total confidence.
---1. Classification and Core Definitions
What is a Mineral?
A mineral is an inorganic essential micronutrient required by the body in relatively small amounts to maintain vital bodily functions, support growth, and drive metabolic processes. Because they are inorganic, minerals do not contain carbon and are not broken down by heat, light, or digestion.
Macro-minerals vs Trace Elements
In nutrition, minerals are divided into two main categories based on how much our bodies need daily:
• Macro-minerals (Major Minerals): Needed in larger amounts (measured in grams or hundreds of milligrams per day). Examples include: Calcium (\(Ca\)), Sodium (\(Na\)), Potassium (\(K\)), Magnesium (\(Mg\)), and Phosphorus (\(P\)).
• Micro-minerals (Trace Elements): Needed in very small (trace) quantities (often measured in milligrams or micrograms per day). Examples include: Iron (\(Fe\)), Zinc (\(Zn\)), and Iodine (\(I\)).
Understanding Dietary Reference Values (DRVs)
When studying minerals, you will encounter the UK framework for Dietary Reference Values (DRVs). Here is what those key acronyms mean in your exam:
• RNI (Reference Nutrient Intake): The intake of a nutrient that is sufficient to meet the dietary needs of almost all (\(97.5\%\)) healthy individuals within a specific group.
• EAR (Estimated Average Requirement): An estimate of the average requirement of energy or a nutrient needed by a group of people; it meets the needs of \(50\%\) of the population.
• LRNI (Lower Reference Nutrient Intake): The level of intake that meets the needs of only \(2.5\%\) of people. Intakes below the LRNI are almost certainly inadequate for most individuals.
• Safe Intake: A term used when there is not enough reliable scientific evidence to establish an EAR, RNI, or LRNI, but an intake range is known to be sufficient without causing adverse effects.
Key Takeaway: Macro-minerals are required in larger amounts, while trace elements are needed in tiny quantities. Remember that the RNI is designed to cover \(97.5\%\) of the population, not just the average person!
---2. Calcium (\(Ca\))
Calcium is the most abundant mineral in the human body, with around \(99\%\) stored in your skeletal system.
Key Functions of Calcium
• Skeletal Structure: Calcium combines with phosphate to form hydroxyapatite crystals, providing strength and rigidity to bones and teeth.
• Blood Clotting: Calcium acts as an essential cofactor in the blood clotting cascade, helping convert prothrombin to thrombin to form a protective fibrin mesh.
• Muscle Contraction: It allows muscle fibres (including the heart muscle) to slide and contract properly.
• Nerve Transmission: Facilitates the release of neurotransmitters so nerve impulses travel seamlessly across synapses.
Primary Food Sources
• Milk, hard and soft cheeses, and yoghurt.
• Calcium-fortified plant-based milks (e.g., soya, oat, almond).
• Canned oily fish eaten with edible soft bones (e.g., sardines, canned salmon).
• Green leafy vegetables (e.g., kale, broccoli).
• Fortified white flour and white bread (by UK law).
Bioavailability: What Helps and What Hinders Absorption?
Bioavailability means how easily a nutrient can be digested, absorbed, and utilised by the body.
Enhancers (Help Absorption):
• Vitamin D: Active vitamin D (calcitriol) stimulates the production of calcium-binding proteins (calbindin) in the intestinal lining.
• Lactose: The natural sugar in milk promotes a lower gut pH, keeping calcium soluble.
• Acidic Environment: Stomach acid keeps calcium dissolved for easy mucosal absorption.
Inhibitors (Hinder Absorption):
• Phytates (Phytic Acid): Found in unrefined cereals, bran, and pulses; binds with calcium to form insoluble complexes.
• Oxalates (Oxalic Acid): Found in spinach and rhubarb; binds tightly to calcium.
• Excess Dietary Fibre: Speeds up intestinal transit time, reducing contact time.
• Unabsorbed Fatty Acids: Form insoluble "calcium soaps" that are excreted in stools.
Deficiency and Excess Risks
• Deficiency Conditions:
- Rickets in children: Soft, weak, malformed bones leading to bowed legs.
- Osteomalacia in adults: "Soft bones" caused by demineralisation, leading to bone pain and muscle weakness.
- Osteoporosis: Long-term negative calcium balance causing low bone mineral density and porous, brittle bones prone to fracture.
- Hypocalcaemia / Tetany: Very low blood calcium leading to uncontrolled muscle twitches and spasms.
• Excess / Toxicity:
- Hypercalcaemia: Can impair kidney function and cause kidney stones.
- Mineral Competition: High calcium intake can inhibit the absorption of other essential minerals like iron and zinc.
Key Takeaway: Calcium cannot build strong bones alone—it requires Vitamin D for intestinal absorption and Phosphorus to form hydroxyapatite crystals!
---3. Iron (\(Fe\))
Iron is an essential trace element that plays a central role in energy production and oxygen delivery.
Key Functions of Iron
• Haemoglobin Formation: Core component of haemoglobin within red blood cells (erythrocytes) to transport oxygen from the lungs to all living tissues.
• Myoglobin Formation: Component of myoglobin, an oxygen-binding protein in muscle tissue that stores oxygen for muscle work.
• Cellular Energy Metabolism: Essential cofactor for cytochromes involved in mitochondrial ATP (energy) production.
Two Forms of Dietary Iron: Haem vs Non-Haem
Understanding the difference between these two chemical forms is one of the most frequently tested topics in AS 1:
1. Haem Iron (Ferrous Form: \(Fe^{2+}\)):
• Where it is found: Animal flesh (red meat, offal such as liver, poultry, fish).
• Bioavailability: High (approx. \(20\text{–}30\%\) absorbed).
• Why? It is absorbed intact inside the haem ring structure and is largely unaffected by dietary inhibitors.
2. Non-Haem Iron (Ferric Form: \(Fe^{3+}\)):
• Where it is found: Plant foods (beans, lentils, chickpeas, dark green leafy vegetables, dried fruit) and fortified breakfast cereals.
• Bioavailability: Low (approx. \(2\text{–}8\%\) absorbed).
• Why? Must be chemically reduced to the soluble ferrous form (\(Fe^{2+}\)) in the stomach before it can be absorbed.
Bioavailability: Enhancers and Inhibitors
• Enhancers:
- Vitamin C (Ascorbic Acid): Acts as a reducing agent that converts insoluble ferric iron (\(Fe^{3+}\)) into soluble, absorbable ferrous iron (\(Fe^{2+}\)).
- Meat/Fish Protein Factor: Eating meat/fish alongside plant sources improves non-haem iron absorption.
• Inhibitors:
- Tannins and Polyphenols: Found in tea and coffee; bind iron tightly, preventing absorption.
- Phytates: Found in whole grains, seeds, and unrefined cereals.
- Excess Calcium: Competes directly with iron for mucosal uptake.
- Excess Fibre: Accelerates transit through the digestive tract.
Deficiency and Excess Risks
• Deficiency – Iron Deficiency Anaemia:
When iron stores are depleted, haemoglobin synthesis drops. This results in microcytic (abnormally small) and hypochromic (pale) red blood cells.
Symptoms: Chronic fatigue, lethargy, breathlessness on exertion, pale skin (pallor), reduced cognitive function, and poor concentration.
• Excess / Toxicity:
- High-dose iron supplements cause gastrointestinal irritation, constipation, or nausea.
- Haemochromatosis: A genetic disorder causing excessive, uncontrolled absorption of dietary iron, which accumulates and damages organs like the liver and heart.
Memory Trick: "C makes Fe free!" Remember that Vitamin C frees up non-haem iron (\(Fe^{3+}\)) by converting it into soluble \(Fe^{2+}\).
Key Takeaway: Haem iron (\(Fe^{2+}\)) is easily absorbed from meat, while non-haem iron (\(Fe^{3+}\)) from plant foods requires Vitamin C to maximise absorption.
---4. Sodium (\(Na\)) and Potassium (\(K\))
Sodium and potassium work as a biochemical team to regulate the body's internal fluids and electrical circuitry.
Functions of Sodium and Potassium
• Fluid and Osmotic Balance: Sodium is the principal extracellular cation (fluid outside cells), while Potassium is the principal intracellular cation (fluid inside cells). Together, they regulate osmotic pressure and maintain correct hydration.
• Nerve Impulse Transmission & Muscle Contraction: By swapping across cell membranes via the sodium-potassium pump, they create the electrical membrane potentials required for nerve firing and heartbeat regulation.
Sources in the Diet
• Sodium Sources: Table salt (sodium chloride), processed foods, ready meals, bacon, ham, cured meats, crisps, savoury snacks, and bread.
• Potassium Sources: Fresh fruits (bananas, oranges), vegetables (potatoes, leafy greens, tomatoes), pulses, milk, and lean meats.
Health Guidelines, Salt vs Sodium, and Excess Risks
A diet high in sodium and low in potassium is directly linked to hypertension (high blood pressure). Chronic hypertension puts immense strain on blood vessels, significantly increasing the risk of coronary heart disease (CHD), stroke, and kidney disease.
Examiner Calculation Rule: Salt vs Sodium
Never mix up salt and sodium in your calculations or explanations!
• Salt is sodium chloride (\(\text{NaCl}\)).
• Conversion formula: \(1\text{ g sodium} \approx 2.5\text{ g salt}\)
• UK Government Maximum Guideline for Adults: Maximum \(6\text{ g}\) of salt per day (equivalent to approximately \(2.4\text{ g}\) of sodium).
Key Takeaway: Sodium controls extracellular fluid while potassium controls intracellular fluid. High sodium intakes drive high blood pressure, and adults should consume no more than \(6\text{ g}\) of salt (\(2.4\text{ g}\) sodium) daily.
---5. Other Essential Minerals
Make sure you can identify the key functions and deficiency signs for these additional minerals required by the CCEA specification:
Phosphorus (\(P\))
• Functions: Combines with calcium to form calcium phosphate / hydroxyapatite in bones and teeth; structural component of ATP (adenosine triphosphate) for cellular energy transfer; essential component of phospholipids in all cell membranes.
• Sources: High-protein foods such as dairy products, meat, poultry, fish, eggs, and nuts.
Zinc (\(Zn\))
• Functions: Essential cofactor for DNA and protein synthesis; plays a critical role in immune system function, tissue growth, and wound healing.
• Sources: Red meat, seafood (especially oysters), shellfish, whole grains, and seeds.
• Deficiency Signs: Impaired wound healing, increased susceptibility to infection, delayed growth, and hair loss.
Iodine (\(I\))
• Functions: Required for the synthesis of thyroid hormones: thyroxine (\(T_4\)) and triiodothyronine (\(T_3\)). These hormones regulate the body's Basal Metabolic Rate (BMR), growth, and cellular development.
• Sources: Seafood, marine fish, seaweed, cows' milk, and dairy products (due to cattle feed supplementation).
• Deficiency Signs: Enlargement of the thyroid gland in the neck, known as a goitre, due to overstimulation by the pituitary gland trying to produce thyroid hormones.
Magnesium (\(Mg\))
• Functions: Structural component of bones; vital enzymatic cofactor for over \(300\) biochemical reactions in the body, including the activation of ATP; supports normal muscle contraction and neuromuscular transmission.
• Sources: Green leafy vegetables (component of chlorophyll), whole grains, nuts, seeds, and legumes.
Key Takeaway: Phosphorus builds bones and ATP; Zinc drives healing and immunity; Iodine regulates metabolic rate via thyroid hormones; Magnesium acts as a master cofactor for over \(300\) enzymatic processes.
---6. Exam Pitfalls & How to Avoid Them
Here are common mistakes reported by CCEA examiners and how you can avoid losing easy marks:
1. Mistake: Claiming spinach is as good an iron source as beef.
Correction: Always explain that plant iron is non-haem iron (\(Fe^{3+}\)), which has low bioavailability (\(2\text{–}8\%\)) and contains inhibitors like oxalates and phytates. Haem iron (\(Fe^{2+}\)) from meat is absorbed much more efficiently (\(20\text{–}30\%\)).
2. Mistake: Stating that calcium builds bones on its own.
Correction: Always mention Vitamin D (stimulates calbindin synthesis to absorb calcium) and Phosphorus (forms hydroxyapatite).
3. Mistake: Confusing \(6\text{ g}\) of salt with \(6\text{ g}\) of sodium.
Correction: Remember that the UK target is \(6\text{ g}\) of salt or \(2.4\text{ g}\) of sodium. \(1\text{ g of sodium} \approx 2.5\text{ g of salt}\).
4. Mistake: Just writing "causes anaemia" without detail.
Correction: Specify iron deficiency anaemia, and describe it accurately as producing microcytic (small), hypochromic (pale) red blood cells with reduced oxygen-carrying capacity.
5. Mistake: Defining the RNI as a "minimum requirement for an individual."
Correction: State clearly that the Reference Nutrient Intake (RNI) is a population target calculated to meet the nutritional needs of \(97.5\%\) of healthy people in a group.
7. Quick Revision Summary Checklist
Before sitting your AS 1 exam, make sure you can confidently answer the following:
• Can you define a mineral and differentiate between macro-minerals and trace elements?
• Can you state the differences between RNI, EAR, LRNI, and Safe Intake?
• Can you outline four distinct physiological functions of Calcium?
• Can you list three enhancers and three inhibitors of Calcium and Non-Haem Iron absorption?
• Can you compare Haem (\(Fe^{2+}\)) and Non-Haem (\(Fe^{3+}\)) iron in terms of source and bioavailability?
• Can you define the pathological features of iron deficiency anaemia (microcytic, hypochromic)?
• Can you explain the cellular fluid distribution of Sodium (extracellular) and Potassium (intracellular)?
• Can you state the maximum UK daily salt guideline for adults (\(6\text{ g}\) salt / \(2.4\text{ g}\) sodium)?
• Can you state the core functions of Zinc, Magnesium, Iodine, and Phosphorus?