Micronutrients, Water and Antioxidants
Micronutrients — The Small but Essential Nutrients
Micronutrients are vitamins and minerals needed in tiny quantities — milligrams or micrograms rather than grams. Unlike macronutrients, they do not supply energy; instead they regulate countless body processes, from bone formation to immune defence to energy release from food. Missing even one regularly causes a specific deficiency disease. The exam expects you to know each one’s functions, main sources, and effects of deficiency and excess.
Fat-Soluble Vitamins
Fat-soluble vitamins are stored in the liver and body fat, so they do not need to be eaten every day — but they can build up to toxic levels if consumed in very high doses (excess). There are four: A, D, E and K.
- Vitamin A — needed for vision in dim light (rhodopsin production), healthy skin, and immune function. Sources: liver, oily fish, dairy, eggs; also from beta-carotene in orange and yellow vegetables (carrots, sweet potato, butternut squash). Deficiency causes night blindness and dry skin.
- Vitamin D — essential for absorbing calcium and phosphorus, so it underpins strong bones and teeth. The body makes it when skin is exposed to sunlight; dietary sources include oily fish, eggs, fortified cereals and fortified spreads. Deficiency causes rickets in children and osteomalacia in adults (soft, painful bones).
- Vitamin E — an antioxidant that protects cell membranes from oxidative damage. Sources include vegetable oils, nuts, seeds and avocado. Deficiency is rare in healthy adults but can cause nerve damage.
- Vitamin K — essential for blood clotting and bone health. Main sources: green leafy vegetables (kale, spinach, broccoli), vegetable oils, fermented foods. Deficiency causes impaired blood clotting.
Fat-soluble vitamins A, D, E and K are stored in the liver and body fat. Excess can be toxic. Deficiency of vitamin D causes rickets in children; deficiency of vitamin A causes night blindness.
Water-Soluble Vitamins — The B Group and Vitamin C
Water-soluble vitamins dissolve in water and cannot be stored in large amounts, so they need to be eaten regularly. They are also easily lost during food preparation and cooking — a critical exam point.
- B1 (thiamin) — needed for energy release from carbohydrates. Sources: pork, fortified cereals, nuts, peas. Deficiency causes beriberi (nerve damage, muscle weakness).
- B2 (riboflavin) — supports energy metabolism and healthy skin. Sources: milk, eggs, liver, fortified cereals.
- B3 (niacin) — needed for energy metabolism and DNA repair. Sources: meat, fish, peanuts, fortified flour. Severe deficiency causes pellagra.
- Folic acid (folate) — essential for making new red blood cells and for healthy fetal development (prevents neural tube defects). Sources: green leafy vegetables, beans, fortified bread. Deficiency causes megaloblastic anaemia; pregnant women are advised to supplement.
- B12 (cobalamin) — required for red blood cell formation and maintaining the nervous system. Sources: meat, fish, dairy, eggs (virtually absent from non-fortified plant foods). Deficiency causes megaloblastic anaemia and nerve damage; vegans must supplement or eat fortified foods.
- Vitamin C (ascorbic acid) — needed for collagen synthesis (skin, blood vessels, wound healing), immune function, and iron absorption from plant foods. Sources: fresh fruit (oranges, kiwi, strawberries), peppers, broccoli, potatoes. Deficiency causes scurvy (bleeding gums, slow wound healing).
Vitamins C and the B-group are water-soluble and heat-sensitive, so they leach into cooking water and are destroyed by prolonged heat. When you boil broccoli, the vitamin C and folate dissolve into the water — which is then poured down the drain. To minimise losses: use the minimum water possible; steam rather than boil (the food doesn’t sit in water); use short cooking times; prepare vegetables just before cooking (chopping increases surface area and speeds up oxidation); avoid keeping cooked vegetables warm for long periods. These facts are frequently tested with a “describe” command word.
Key Minerals
The spec lists six minerals you must know: calcium, iron, sodium, fluoride, iodine and phosphorus.
- Calcium — builds and maintains bones and teeth, assists muscle contraction and nerve function. Sources: milk, cheese, yoghurt, fortified plant milks, canned fish with bones (sardines), dark green vegetables. Deficiency causes rickets (children) or osteoporosis (adults).
- Iron — needed for making haemoglobin, which carries oxygen in red blood cells. Sources: red meat (haem iron, absorbed most efficiently), liver, fortified cereals, lentils, dark green vegetables. Deficiency causes iron-deficiency anaemia (fatigue, pale skin, breathlessness). Vitamin C consumed at the same meal increases non-haem iron absorption from plant foods.
- Sodium (salt) — regulates fluid balance and nerve impulses. Too much raises blood pressure (hypertension), increasing the risk of stroke and CHD. Most dietary sodium comes from processed foods. The Reference Intake for adults is 2.4 g sodium (6 g salt) per day.
- Fluoride — strengthens tooth enamel and reduces tooth decay. Sources: fluoridated water, tea, fish. Excess causes dental fluorosis (mottled teeth).
- Iodine — essential for making thyroid hormones, which regulate metabolism. Sources: milk, dairy, seafood, some fortified foods. Deficiency causes goitre (enlarged thyroid gland) and, in pregnancy, can impair the baby’s brain development.
- Phosphorus — works alongside calcium to build bones and teeth; also involved in energy metabolism. Sources: meat, fish, dairy, eggs, cereals.
Iron makes haemoglobin to carry oxygen in blood. Deficiency causes iron-deficiency anaemia. Calcium builds bones and teeth; deficiency causes rickets (children) or osteoporosis (adults). Vitamin C increases absorption of non-haem iron from plant sources.
Antioxidants — Protecting Cells from Damage
Antioxidants neutralise free radicals — unstable molecules that damage cell membranes and DNA. The three antioxidant vitamins on the spec are:
- Vitamin A (from beta-carotene in plant foods) — protects cells in the respiratory and digestive tracts.
- Vitamin C — water-soluble antioxidant; active in the fluid inside cells and in blood plasma.
- Vitamin E — fat-soluble antioxidant; embedded in cell membranes where it prevents oxidative damage to fats.
Eating a diet rich in colourful fruits and vegetables — a Greek salad of tomatoes, peppers, cucumber and olive oil, or a fruit salad of kiwi, strawberries and orange — provides a wide range of antioxidants. This is part of the evidence base behind the government’s five-a-day guidance.
Many students incorrectly state that all vitamins are lost when you boil vegetables. Only water-soluble vitamins (B-group and C) leach into cooking water. Fat-soluble vitamins (A, D, E and K) do not dissolve in water and are not lost by boiling — though they can be damaged by prolonged very high heat. The practical implication is: to preserve vitamin C in a stir-fry, use high heat for a short time with very little water; to preserve vitamin C in boiled broccoli, steam instead and serve immediately.
Water and Hydration
Water is not classified as a macronutrient or micronutrient but is essential for life. Its key functions are: transporting nutrients and oxygen in the blood; removing waste products as urine; regulating body temperature through sweating; acting as a lubricant in joints; and supporting digestion. The body loses water through breathing, sweating, urinating and in faeces. Adults should drink approximately 6–8 cups (around 1.5–2 litres) of fluid per day. More is needed in hot weather, during exercise, and when ill. Dehydration causes headaches, fatigue, reduced concentration and, in severe cases, organ failure.