Welcome to Vitamins for AS 1: Principles of Nutrition
Welcome to your study notes on Vitamins for CCEA AS Level Nutrition and Food Science! Vitamins are vital organic micronutrients. Even though our bodies only require them in tiny amounts (milligrams or micrograms), they play massive roles in keeping us healthy, energized, and protected from disease.
Don't worry if the chemical names or metabolic functions seem overwhelming at first. We will break everything down into bite-sized, logical chunks with memory tricks, real-world examples, and clear pointers on exactly what examiners expect in your AS 1 examination.
1. Classification: Fat-Soluble vs. Water-Soluble
Vitamins are grouped according to how they dissolve and absorb in the body. This single chemical difference determines where they come from, how our body stores them, how often we must eat them, and how easily they are destroyed during cooking.
• Fat-Soluble Vitamins: Vitamins A, D, E, and K.
Memory Aid: Remember the word ADEK. These vitamins dissolve in dietary fats, are absorbed along with lipids in the small intestine, and can be stored in large quantities in the liver and fatty (adipose) tissue. Because we store them, we do not need them every single day, but consuming far too much can lead to toxic build-up (known as hypervitaminosis).
• Water-Soluble Vitamins: The B-Complex group (\(B_1\), \(B_2\), \(B_3\), \(B_6\), \(B_9\)/folate, and \(B_{12}\)) and Vitamin C (ascorbic acid).
These vitamins dissolve in water and are not stored in significant amounts. Excess quantities are filtered out by the kidneys and excreted in urine. As a result, we need a steady, daily dietary supply. They are also easily lost during food preparation and cooking because they dissolve into cooking water and degrade when exposed to heat.
Quick Key Takeaway: Fat-soluble vitamins (\(A, D, E, K\)) are stored in body fat and liver (risk of toxicity if over-consumed). Water-soluble vitamins (\(B\)-group and \(C\)) are excreted regularly, requiring frequent intake and careful cooking methods to avoid nutrient loss.
2. The Fat-Soluble Vitamins (A, D, E, K)
Vitamin A (Retinoids and Carotenoids)
Vitamin A exists in our diet in two distinct chemical forms:
• Retinol (Pre-formed Vitamin A): Found exclusively in animal sources such as liver, oily fish, egg yolk, dairy products, and fortified fat spreads.
• Beta-Carotene (Provitamin A): An orange/yellow pigment found in plant sources that the body converts into retinol. Rich sources include carrots, sweet potatoes, yellow/orange peppers, apricots, and dark green leafy vegetables like spinach and kale.
Biological Functions:
1. Vision in Dim Light: Vitamin A binds with the protein opsin to form rhodopsin (visual purple) in the rod cells of the retina. This allows the eye to adapt to low light.
2. Epithelial Cell Health & Immunity: It maintains the health and integrity of mucosal barriers and epithelial tissues (the skin, respiratory lining, and digestive tract), preventing pathogen entry.
3. Cell Differentiation and Antioxidant Defence: Beta-carotene acts as an antioxidant, helping neutralise damaging free radicals.
Deficiency Effects:
• Night Blindness (Nyctalopia): Inability of the eyes to adapt to low light due to impaired rhodopsin regeneration.
• Xerophthalmia: A severe, progressive condition where the cornea becomes dry, keratinised, and ulcerated, ultimately causing irreversible blindness.
• Increased Infection Risk: Weakened epithelial linings lead to higher vulnerability to respiratory and gastrointestinal infections.
Toxicity & Vulnerable Groups:
Excess pre-formed retinol is teratogenic (causes congenital abnormalities/birth defects in the developing foetus). Therefore, pregnant women (or women planning a pregnancy) are advised to avoid liver, liver products (such as pâté), and high-dose retinol supplements. Chronic high intake in adults can also lead to liver damage and bone thinning.
Examiner Note: High intakes of beta-carotene do not cause teratogenic toxicity; they simply turn the skin a harmless yellowish-orange colour (carotenodermia).
Vitamin D (Calciferols)
Often called the "sunshine vitamin," Vitamin D acts more like a hormone than a classic dietary nutrient.
• Chemical Forms: Cholecalciferol (\(D_3\)), which is synthesised in the skin upon exposure to ultraviolet B (UVB) sunlight and found in animal foods; and Ergocalciferol (\(D_2\)), found in plant and fungal sources.
• Main Sources: Direct skin exposure to sunlight (UVB); oily fish (salmon, mackerel, sardines), egg yolks, and fortified products (fortified breakfast cereals and spreads).
Biological Functions:
• Promotes the intestinal absorption of calcium and phosphorus.
• Regulates blood calcium homeostasis and ensures proper mineralisation of bones and teeth.
• Supports normal muscle function.
Deficiency Conditions:
• Rickets (in Children): Failure of growing bones to mineralise properly, resulting in soft, pliable bones that bend under body weight (leading to characteristic bowed legs or knocked knees).
• Osteomalacia (in Adults): Incomplete mineralisation of the bone matrix, causing bone softening, severe bone pain, and muscle weakness.
Government Recommendations & High-Risk Groups:
In the UK, skin synthesis of Vitamin D is negligible between October and March due to the angle of sunlight. Public health guidelines (SACN) advise that all individuals over 1 year of age consider a daily supplement of \(10\ \mu\text{g}\) during autumn and winter.
Vulnerable groups require a \(10\ \mu\text{g}\) supplement year-round, including: breastfed infants, individuals who spend little time outdoors (e.g. frail or institutionalised people), individuals who wear concealing clothing, and people with darker skin pigmentation (as melanin reduces UVB absorption).
Toxicity: Excessive supplementation causes hypercalcaemia (dangerously high blood calcium), leading to calcium deposits in soft tissues (such as blood vessels and kidneys) and kidney damage.
Vitamin E (Tocopherols)
• Chemical Form: The most biologically active form is \(\alpha\)-tocopherol.
• Biological Function: Acts as a primary fat-soluble antioxidant. It protects polyunsaturated fatty acids (PUFAs) in cell membranes from lipid peroxidation caused by reactive free radicals.
• Sources: Plant and vegetable oils (sunflower, olive, rapeseed), nuts, seeds, wheat germ, and green leafy vegetables.
• Deficiency & Toxicity: Deficiency is very rare, though premature infants may experience haemolytic anaemia (breakdown of red blood cell membranes). Toxicity is low, but extreme doses may interfere with Vitamin K action.
Vitamin K (Phylloquinone & Menaquinone)
• Chemical Forms: \(K_1\) (phylloquinone) from plant foods and \(K_2\) (menaquinone) synthesised by normal gut microflora bacteria.
• Biological Function: Essential cofactor for the carboxylation of glutamate residues needed for blood clotting proteins (such as prothrombin and clotting factors VII, IX, and X). It is also involved in bone metabolism via the protein osteocalcin.
• Sources: Green leafy vegetables (broccoli, spinach, Brussels sprouts, kale), vegetable oils, and fermented foods.
• Deficiency: Causes prolonged blood clotting times and haemorrhage. Newborn babies have sterile guts (no bacteria to make \(K_2\)) and low placental transfer, putting them at risk of Haemorrhagic Disease of the Newborn (HDN). Consequently, newborns are routinely given a prophylactic dose of Vitamin K at birth.
Fat-Soluble Summary Box:
• Vitamin A: Vision (rhodopsin) + epithelial barrier. Retinol (animal/teratogenic in pregnancy) vs Beta-carotene (plants).
• Vitamin D: Calcium absorption + bone health. Deficiency: Rickets (kids) / Osteomalacia (adults). \(10\ \mu\text{g}\) advice in winter.
• Vitamin E: Fat-soluble antioxidant protecting cell membranes.
• Vitamin K: Blood clotting (prothrombin). Prophylactic injection given to newborns.
3. The Water-Soluble Vitamins (B-Complex and Vitamin C)
The B-Complex Group
The B vitamins act primarily as coenzymes in cellular metabolism, helping unlock energy from carbohydrates, fats, and proteins.
1. Thiamin (Vitamin \(B_1\)):
• Function: Coenzyme (TPP) for carbohydrate metabolism and essential for normal nerve and muscle function.
• Sources: Whole grains, fortified breakfast cereals/flour, pork, nuts, and pulses.
• Deficiency: Beriberi (can present as 'Wet Beriberi' with heart failure and oedema, or 'Dry Beriberi' with nerve wasting and paralysis). Also seen as Wernicke-Korsakoff syndrome in chronic alcohol misuse.
2. Riboflavin (Vitamin \(B_2\)):
• Function: Essential structural component of the coenzymes FMN and FAD, which drive cellular energy release in the electron transport chain.
• Sources: Milk, yoghurt, cheese, eggs, and fortified cereals.
• Deficiency: Ariboflavinosis, characterised by cracks at the corners of the mouth (angular stomatitis), chapped/inflamed lips (cheilosis), and a swollen, magenta-coloured tongue (glossitis).
Exam Tip: Riboflavin is light-sensitive. Storing milk in clear glass bottles exposed to daylight degrades its \(B_2\) content quickly!
3. Niacin (Vitamin \(B_3\)):
• Function: Forms the coenzymes NAD and NADP, essential for oxidative cellular respiration and energy production. The body can also synthesise small amounts of niacin from the essential amino acid tryptophan.
• Sources: Meat, poultry, fish, fortified flour/breakfast cereals, and peanuts.
• Deficiency: Pellagra. Remember the 4 Ds: Dermatitis (scaly rash on sun-exposed skin), Diarrhoea, Dementia (confusion and memory loss), and eventually Death if untreated.
4. Vitamin \(B_6\) (Pyridoxine):
• Function: Coenzyme in amino acid metabolism, transamination reactions, synthesis of neurotransmitters (e.g. serotonin), and haemoglobin formation.
• Sources: Poultry, white fish, potatoes, chickpeas, bananas, and whole grains.
• Deficiency: Microcytic anaemia, depression, confusion, and peripheral neuropathy.
5. Folate / Folic Acid (Vitamin \(B_9\)):
• Function: Crucial for one-carbon transfers, DNA synthesis, cell division, and healthy red blood cell maturation.
• Sources: Green leafy vegetables (spinach, kale), fortified breakfast cereals, pulses, oranges, and liver.
• Deficiency:
1. Megaloblastic / Macrocytic Anaemia: Bone marrow releases large, immature, dysfunctional red blood cells because DNA replication is stalled.
2. Neural Tube Defects (NTDs): Inadequate maternal folate levels during early embryonic development prevent proper closure of the neural tube, leading to conditions like spina bifida (where the spinal cord fails to close properly) and anencephaly.
• Public Health Directive: All women planning a pregnancy and those in the first 12 weeks of pregnancy are advised to take a daily supplement of \(400\ \mu\text{g}\) of folic acid to reduce the risk of NTDs.
6. Vitamin \(B_{12}\) (Cobalamin):
• Function: Essential for DNA synthesis, normal neurological function (maintaining the protective myelin sheath around nerves), and metabolising folate into its active form.
• Absorption Requirement: Absorption requires Intrinsic Factor (IF), a glycoprotein produced by parietal cells in the stomach lining.
• Sources: Almost exclusively found in animal products (meat, oily fish, eggs, dairy) and specially fortified foods (fortified breakfast cereals, fortified plant milks, yeast extract).
• Deficiency:
1. Pernicious Anaemia: An autoimmune condition where the body attacks its own stomach lining, failing to produce Intrinsic Factor, preventing \(B_{12}\) absorption.
2. Megaloblastic Anaemia: Identical red blood cell defects to folate deficiency.
3. Irreversible Neurological Damage: Subacute combined degeneration of the spinal cord, causing numbness, ataxia, and cognitive decline.
Critical Vegan Note: Unfortified plant foods (such as spirulina, algae, or mushrooms) do not contain active \(B_{12}\). Strict vegans must consume fortified foods or daily supplements.
Vitamin C (Ascorbic Acid)
Vitamin C is a powerful water-soluble antioxidant and enzymatic cofactor.
Biological Functions:
1. Collagen Synthesis: Essential for the hydroxylation of proline and lysine amino acids during collagen manufacture. Collagen provides the structural scaffolding for skin, blood vessels, bone matrix, cartilage, and healing wounds.
2. Non-Haem Iron Absorption: Vitamin C acts as a reducing agent in the gut, converting non-haem ferric iron (\(\text{Fe}^{3+}\)) to the more soluble and absorbable ferrous form (\(\text{Fe}^{2+}\)).
3. Antioxidant Defence: Scavenges aqueous free radicals and protects cellular components.
4. Immune Support & Wound Healing: Supports white blood cell activity and tissue repair.
Sources:
Citrus fruits (oranges, lemons, grapefruits), blackcurrants, strawberries, kiwi fruit, bell peppers, broccoli, tomatoes, and new potatoes.
Deficiency (Scurvy):
When collagen cannot form its stable triple-helix structure, connective tissues break down. Symptoms include:
• Swollen, bleeding gums and loose teeth.
• Petechiae (tiny pinpoint skin haemorrhages) and easy bruising.
• Poor wound healing and reopening of old scar tissue.
• Joint pain and fatigue.
Cooking Stability & Losses:
Vitamin C is the most fragile vitamin in the human diet. It is destroyed by:
• Leaching: Dissolving rapidly into cooking water when vegetables are boiled.
• Heat: It is thermolabile and degrades during prolonged boiling or warm holding.
• Oxidation: Degrades when exposed to air (oxygen), light, or alkaline conditions (e.g. adding bicarbonate of soda to keep vegetables green).
Preparation Tip: To preserve Vitamin C, chop vegetables immediately before cooking, use minimal water (steaming or microwaving), cover with a tight lid, and cook for the shortest possible time.
Water-Soluble Summary Box:
• \(B_1\) (Thiamin): Beriberi (wet/dry).
• \(B_2\) (Riboflavin): Ariboflavinosis (angular stomatitis, cheilosis). Light-sensitive.
• \(B_3\) (Niacin): Pellagra (4 Ds: Dermatitis, Diarrhoea, Dementia, Death). Made from tryptophan.
• \(B_6\) (Pyridoxine): Protein/amino acid metabolism & neurotransmitters.
• \(B_9\) (Folate): DNA synthesis. Prevents Neural Tube Defects (take \(400\ \mu\text{g}\) in pregnancy) & Megaloblastic anaemia.
• \(B_{12}\) (Cobalamin): Animal foods only. Needs Intrinsic Factor. Deficiency: Pernicious anaemia & nerve damage.
• Vitamin C: Collagen synthesis, \(\text{Fe}^{3+} \to \text{Fe}^{2+}\) iron absorption, antioxidant. Deficiency: Scurvy. Very heat/water sensitive.
4. Common Exam Pitfalls to Avoid in AS 1
1. Mixing up Anaemias:
• Iron-deficiency anaemia produces microcytic (small) and hypochromic (pale) red blood cells due to lack of haemoglobin.
• Folate or Vitamin \(B_{12}\) deficiency produces macrocytic / megaloblastic (enlarged, immature) red blood cells due to impaired DNA replication.
• Pernicious anaemia specifically refers to \(B_{12}\) deficiency caused by an autoimmune absence of Intrinsic Factor.
2. Assuming Beta-Carotene is Toxic:
Pre-formed retinol causes birth defects in pregnancy and liver damage at high doses. Beta-carotene does not convert to retinol rapidly enough to cause toxicity; it only causes harmless skin discolouration.
3. Misidentifying Vegan \(B_{12}\) Sources:
Do not write that mushrooms, seaweed, or unfortified plant foods provide reliable \(B_{12}\). They contain inactive pseudovitamin analogues. Only fortified foods or supplements are biologically available for vegans.
4. Forgetting Nutrient Synergy:
Always connect paired nutrients in your extended answers:
• Vitamin C + Iron: Vitamin C reduces non-haem \(\text{Fe}^{3+}\) to absorbable \(\text{Fe}^{2+}\).
• Vitamin D + Calcium: Vitamin D is mandatory for intestinal calcium absorption and bone mineralisation.
5. Quick Knowledge Check
• Why do newborns receive a Vitamin K injection? Their sterile gut has not yet developed the microflora to synthesise \(K_2\), putting them at risk of haemorrhage (HDN).
• What is the official UK guidance for Vitamin D? A daily supplement of \(10\ \mu\text{g}\) during autumn and winter for all over age 1 (and year-round for high-risk groups).
• What is the official recommendation for folic acid in pregnancy? A daily supplement of \(400\ \mu\text{g}\) prior to conception and up to the 12th week of pregnancy to prevent Neural Tube Defects like spina bifida.