State the causes and effects of vitamin D and iron deficiencies.

7.1 Human Nutrition – Diet

Objective

State the causes and effects of vitamin D and iron deficiencies and relate them to the wider IGCSE Biology topics of balanced diet, digestion and absorption.

Context within the Cambridge IGCSE (0610) syllabus

The material on vitamin D and iron deficiencies links the following sub‑topics:

• 7.1 – Balanced diet & principal dietary sources
• 7.2 – The digestive system (organs & functions)
• 7.3 – Physical digestion
• 7.4 – Chemical digestion
• 7.5 – Absorption
• 7.6 – Transport of gases (haemoglobin)
• 7.7 – Immunity and disease (effects of deficiency)
• 7.8 – Drugs (antibiotics & resistance – brief note)
• 20 – Human influences on ecosystems (nutrient cycles – brief note)

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7.1 – Balanced diet & principal dietary sources

Major food groups (recommended daily amounts for a typical 14‑year‑old)

Food group	Key nutrients	Typical daily portion
Starchy carbohydrates (cereals, potatoes, rice, pasta)	Carbohydrates, B‑vitamins, fibre	6–8 portions (≈ 400 g)
Fruits & vegetables	Vitamins A, C, K, folate, fibre, minerals	5–7 portions (≈ 400 g)
Protein foods (meat, fish, eggs, beans, nuts)	Protein, iron, zinc, B‑vitamins	2–3 portions (≈ 70 g protein)
Dairy & calcium‑rich alternatives	Calcium, vitamin D (fortified), protein, riboflavin	2–3 portions (≈ 500 ml milk or fortified plant drink)
Fats & oils	Essential fatty acids, vitamin E, fat‑soluble vitamins (A, D, E, K)	1–2 teaspoons (≈ 30 g)
Water	Hydration, solvent for metabolic reactions	≈ 1.5–2 L (≈ 8 glasses)

Recommended daily amounts of key micronutrients (typical RDA/DRI for adolescents)

Micronutrient	RDA (≈ 14‑year‑old)	Key food sources
Vitamin C	45 mg	Citrus fruits, strawberries, kiwi, peppers, broccoli
Vitamin D	5 µg (200 IU)	Fortified milk, oily fish (salmon, mackerel), sunlight‑derived
Iron (haem & non‑haem)	11 mg (boys) / 15 mg (girls)	Red meat, poultry, fish, lentils, fortified cereals, dark leafy greens
Calcium	1300 mg	Milk, cheese, yoghurt, fortified soy drinks, tofu with calcium sulfate
Fibre	25 g (girls) / 30 g (boys)	Whole‑grain cereals, fruits, vegetables, legumes, nuts

Key vitamins & minerals mentioned in this lesson

• Vitamin D – calcium absorption, bone mineralisation.
• Vitamin C – collagen synthesis, antioxidant, prevents scurvy.
• Iron – component of haemoglobin, oxygen transport.
• Calcium – bone strength, muscle contraction, nerve transmission.

Related deficiency – Scurvy

• Cause: Very low intake of vitamin C (e.g., diets lacking fresh fruit, citrus, raw vegetables, or reliance on heavily processed foods).
• Effects: Bleeding gums, bruising, poor wound healing, joint pain, anaemia, fatigue.
• Link to balanced diet: Highlights the importance of the fruit & vegetable group for supplying vitamin C.

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7.2 – The digestive system (organs & functions)

• Mouth: Ingestion, mechanical breakdown by teeth, salivary amylase begins carbohydrate digestion.
• Oesophagus: Peristaltic transport of the bolus to the stomach.
• Stomach: Mechanical churning; secretion of gastric juice (hydrochloric acid + pepsin) – HCl denatures proteins and activates pepsin.
• Small intestine (duodenum, jejunum, ileum): Major site of chemical digestion and absorption.
• Liver: Produces bile (stores it in the gall‑bladder) and synthesises many plasma proteins.
• Gall‑bladder: Stores and concentrates bile; releases it into the duodenum in response to fatty meals.
• Pancreas: Releases pancreatic juice containing bicarbonate (neutralises gastric acid) and digestive enzymes (amylase, lipase, trypsin, chymotrypsin).
• Large intestine: Absorbs water and electrolytes; forms and stores faeces.

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7.3 – Physical digestion

• Mastication: Teeth types and their functions
  • Incisors – cut food.
  • Canines – tear food.
  • Premolars & molars – grind and crush food.
• Peristalsis: Wave‑like muscular contractions that move food through the gastrointestinal tract.
• Churning (stomach): Mixing of food with gastric secretions to form a semi‑liquid chyme.

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7.4 – Chemical digestion

Nutrient	Key enzyme(s)	Site of action
Carbohydrates	Salivary amylase, pancreatic amylase, brush‑border maltase, sucrase, lactase	Mouth → duodenum → small‑intestine brush border
Proteins	Pepsin (stomach, activated by HCl), pancreatic proteases (trypsin, chymotrypsin), brush‑border peptidases	Stomach → duodenum → small‑intestine
Lipids	Bile salts (emulsify), pancreatic lipase, brush‑border lipase	Duodenum → small‑intestine

Additional points required by the syllabus

• Hydrochloric acid in the stomach denatures protein structure and creates the optimal pH for pepsin activity.
• Bile, produced by the liver and stored in the gall‑bladder, emulsifies fats, increasing the surface area for pancreatic lipase.

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7.5 – Absorption

• Site: Primarily the jejunum and ileum of the small intestine.
• Structure: Villi (increase surface area); each villus contains a capillary network (water‑soluble nutrients) and a lacteal (lipid‑soluble nutrients).
• Pathways
  • Glucose, amino acids, water‑soluble vitamins → portal blood → liver.
  • Fatty acids & monoglycerides → re‑esterified to triglycerides → chylomicrons → lymphatic system → bloodstream.
  • Fat‑soluble vitamins (A, D, E, K) are absorbed with dietary lipids via the lacteal.
• Large intestine: Re‑absorbs most of the water and electrolytes (Na⁺, Cl⁻, K⁺) left in the chyme; also allows bacterial synthesis of vitamin K.
• Relevance to deficiencies: Malabsorption (e.g., celiac disease) can impair uptake of iron, calcium, and fat‑soluble vitamins such as vitamin D.

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Vitamin D Deficiency

Vitamin D is essential for the intestinal absorption of calcium and for normal bone mineralisation.

Causes

• Insufficient sunlight exposure – high latitudes, indoor lifestyle, extensive sunscreen use.
• Low dietary intake – few fortified foods, limited oily fish, little fortified milk.
• Malabsorption – celiac disease, Crohn’s disease, cystic fibrosis.
• Kidney or liver disease – impaired conversion to the active form calcitriol.
• Dark skin pigmentation – melanin reduces cutaneous synthesis.

Effects

• Reduced calcium absorption → low serum calcium.
• Children: Rickets – soft, weak bones; bowing of legs; delayed growth.
• Adults: Osteomalacia – bone pain, muscle weakness, increased fracture risk.
• Possible contribution to impaired immune function.

Link to syllabus points

• Demonstrates the importance of the absorption process (7.5) for calcium.
• Shows how a deficiency can affect the immune system (topic 7.7) and bone health (topic 7.1).

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Iron Deficiency

Iron is a central component of haemoglobin and many enzymes; its shortage leads to anaemia.

Causes

• Inadequate dietary intake: Low‑iron foods, vegetarian/vegan diets without iron‑rich sources (legumes, dark leafy greens, fortified cereals) or without vitamin C enhancers.
• Increased physiological demand: Rapid growth (children, adolescents), pregnancy & lactation, endurance training.
• Chronic blood loss: Heavy menstrual periods, gastrointestinal bleeding (ulcers, parasites, haemorrhoids).
• Malabsorption: Celiac disease, Helicobacter pylori infection, post‑gastric‑surgery.
• Special groups: Low‑birth‑weight infants, infants fed unfortified formula.

Effects

• Iron‑deficiency anaemia:
  • Reduced haemoglobin → ↓ oxygen transport.
  • Symptoms – fatigue, pallor, breathlessness, tachycardia, reduced exercise tolerance.
  • Impaired cognitive development and poorer school performance in children.
  • Decreased immune function → higher infection risk.
• Pica – craving for non‑food items such as ice, clay or soil.
• Severe cases may develop a heart murmur and cardiac enlargement.

Link to syllabus points

• Illustrates consequences of poor absorption (7.5) and chronic loss on the circulatory system (transport of gases).
• Connects to immunity (7.7) and to the role of haemoglobin in oxygen transport (7.6).

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Summary Comparison

Deficiency	Primary Causes	Key Effects
Vitamin D	Insufficient sunlight (high latitude, indoor life, sunscreen) Poor dietary intake (few fortified foods, little oily fish) Malabsorption or liver/kidney disease Dark skin pigmentation	Rickets (children) or osteomalacia (adults) Bone pain, muscle weakness, increased fracture risk Low serum calcium Possible reduced immune competence
Iron	Low‑iron diet (especially without vitamin C enhancers) Increased demand (growth, pregnancy, endurance training) Chronic blood loss (menstruation, GI bleeding) Malabsorption (celiac, H. pylori, post‑surgery)	Iron‑deficiency anaemia – fatigue, pallor, breathlessness, tachycardia Impaired cognition & school performance Reduced immunity, higher infection risk Pica; severe cases → cardiac enlargement

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Additional syllabus links

Drugs (7.8)

• Antibiotics – used to treat bacterial infections; over‑use can lead to resistance.
• Resistance – microbes develop mechanisms (e.g., enzyme production, altered targets) that render antibiotics less effective.

Human influences on ecosystems (Topic 20)

• Excessive use of fertilisers and pesticides can alter nitrogen and phosphorus cycles, affecting plant nutrient content and, consequently, human nutrition.
• Pollution of water bodies can reduce the availability of safe fish and shellfish, impacting dietary sources of vitamin D and iron.