Water-Soluble Vitamins: B Group (B1, B2, B3)

This lesson covers three of the B group vitamins — Thiamin (B1), Riboflavin (B2), and Niacin (B3) — as required by AQA GCSE Food Preparation and Nutrition (8585), specification section 3.2.2. The B vitamins are all water-soluble, meaning they dissolve in water, are not stored in the body (with the exception of B12), and excess amounts are excreted in urine. This means they must be consumed regularly as part of the diet.

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Properties of Water-Soluble Vitamins

Before looking at individual B vitamins, it is important to understand the general properties of water-soluble vitamins:

Property	Detail
Dissolve in water	They dissolve in the water content of food and in cooking water.
Not stored in the body	Excess is excreted in urine (except Vitamin B12, which is stored in the liver).
Must be consumed regularly	Because they are not stored, a regular dietary intake is needed.
Lost during cooking	They can leach into cooking water, be destroyed by heat, and be affected by exposure to air and light.
Absorbed in the small intestine	They are absorbed directly into the bloodstream.

graph TD
    A["Water-Soluble Vitamins"] --> B["B Group"]
    A --> C["Vitamin C"]
    B --> D["B1 — Thiamin"]
    B --> E["B2 — Riboflavin"]
    B --> F["B3 — Niacin"]
    B --> G["B9 — Folic Acid"]
    B --> H["B12 — Cobalamin"]

    style A fill:#2980b9,color:#fff
    style D fill:#1abc9c,color:#fff
    style E fill:#1abc9c,color:#fff
    style F fill:#1abc9c,color:#fff
    style G fill:#16a085,color:#fff
    style H fill:#16a085,color:#fff
    style C fill:#3498db,color:#fff

Exam Tip: The key difference between fat-soluble and water-soluble vitamins is storage. Fat-soluble vitamins are stored in the body; water-soluble vitamins (except B12) are not. This means water-soluble vitamins must be eaten more frequently and are more easily lost during food preparation and cooking.

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Vitamin B1 — Thiamin

Functions of Thiamin

Function	Detail
Energy release from carbohydrates	Thiamin is a coenzyme involved in the metabolic reactions that release energy from carbohydrate-rich foods. Without thiamin, the body cannot efficiently convert glucose into energy.
Nervous system function	Thiamin is important for the normal functioning of the nervous system, including the transmission of nerve impulses.
Heart function	Adequate thiamin is necessary for normal cardiac (heart) muscle function.

Sources of Thiamin

Source Type	Examples
Cereals and grains	Wholemeal bread, fortified breakfast cereals, brown rice, oats
Meat	Pork (one of the richest sources), liver
Pulses	Peas, beans, lentils
Nuts and seeds	Sunflower seeds, macadamia nuts
Fortified foods	White and brown flour in the UK is fortified with thiamin by law

Exam Tip: Remember that in the UK, all wheat flour (except wholemeal) must be fortified with thiamin, niacin, iron, and calcium by law. This is a useful piece of information that shows real-world application of nutritional knowledge.

Deficiency of Thiamin

• Beri-beri — the classic deficiency disease. There are two forms:
  • Wet beri-beri — affects the cardiovascular system, causing heart failure and fluid retention.
  • Dry beri-beri — affects the nervous system, causing nerve damage, muscle wasting, and difficulty walking.
• Tiredness and weakness — reduced energy release from carbohydrates causes fatigue.
• Beri-beri is rare in the UK but still occurs in some developing countries where polished (white) rice is the dietary staple, as the refining process removes the thiamin-rich bran.

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Vitamin B2 — Riboflavin

Functions of Riboflavin

Function	Detail
Energy release	Like thiamin, riboflavin acts as a coenzyme in metabolic reactions that release energy from proteins, fats, and carbohydrates.
Healthy skin	Riboflavin helps maintain healthy skin, particularly around the mouth, nose, and eyes.
Healthy eyes	It contributes to maintaining normal vision and helps prevent light sensitivity.
Red blood cell production	Riboflavin is involved in the formation of red blood cells.

Sources of Riboflavin

Source Type	Examples
Dairy	Milk, cheese, yoghurt (milk is one of the best sources in the UK diet)
Eggs
Meat	Liver, kidney
Fortified cereals	Many breakfast cereals are fortified with riboflavin
Green vegetables	Broccoli, spinach, asparagus
Yeast extract	Marmite

Exam Tip: Milk is the single most important source of riboflavin in the UK diet. If a question asks about the nutritional impact of removing dairy from the diet, riboflavin deficiency is a key point to mention alongside calcium.

Deficiency of Riboflavin

• Ariboflavinosis — the medical term for riboflavin deficiency. Symptoms include:
  • Cracked, sore lips (cheilosis) — cracking at the corners of the mouth.
  • Sore, swollen tongue (glossitis) — the tongue may become magenta in colour.
  • Dry, flaky skin — particularly around the nose and mouth.
  • Sore, itchy eyes — sensitivity to bright light.
• Deficiency is uncommon in the UK due to the widespread consumption of dairy products and fortified cereals.

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Vitamin B3 — Niacin (Nicotinic Acid / Nicotinamide)

Functions of Niacin

Function	Detail
Energy release	Niacin is a coenzyme (as NAD and NADP) involved in energy-releasing reactions from carbohydrates, fats, and proteins.
Healthy skin	Niacin helps maintain the health and integrity of the skin.
Nervous system	It is important for normal functioning of the nervous system.
Digestive system	Niacin supports normal function of the digestive system.

Sources of Niacin

Source Type	Examples
Meat and poultry	Chicken, turkey, beef, pork, liver
Fish	Tuna, salmon, mackerel
Cereals and grains	Wholemeal bread, fortified breakfast cereals, fortified white flour
Pulses	Peanuts (very rich source), beans, lentils
Other	Mushrooms, potatoes

The body can also synthesise niacin from the amino acid tryptophan (found in protein-rich foods such as meat, fish, eggs, and dairy). This means that a diet adequate in protein is also likely to provide sufficient niacin.

Deficiency of Niacin

• Pellagra — the classic deficiency disease, characterised by the "3 Ds":
  1. Dermatitis — rough, darkened skin, especially on sun-exposed areas.
  2. Diarrhoea — digestive system inflammation.
  3. Dementia — confusion, memory loss, and mental disturbance.
  • A fourth "D" — Death — can occur if pellagra is left untreated.
• Pellagra is rare in the UK but historically occurred in populations whose diet was heavily based on maize (corn), which contains niacin in a form the body cannot absorb (bound niacin).

Exam Tip: The "3 Ds of pellagra" (dermatitis, diarrhoea, dementia) is a classic exam answer. If you are asked about niacin deficiency, state the name of the disease (pellagra) and list the three Ds.

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Comparing B1, B2, and B3

Feature	Thiamin (B1)	Riboflavin (B2)	Niacin (B3)
Key function	Energy from carbohydrates	Energy from food; skin and eyes	Energy from food; skin and nervous system
Best sources	Pork, wholemeal bread, fortified flour	Milk, cheese, eggs, liver	Chicken, fish, peanuts, fortified flour
Deficiency disease	Beri-beri	Ariboflavinosis	Pellagra
Deficiency symptoms	Nerve damage, heart problems, fatigue	Cracked lips, sore tongue, dry skin	Dermatitis, diarrhoea, dementia
UK fortification	Added to white/brown flour	Added to some cereals	Added to white/brown flour
Excess	Excreted in urine	Excreted in urine	Excreted in urine

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The Role of B Vitamins in Energy Release

All three B vitamins covered in this lesson function as coenzymes — they assist enzymes in metabolic reactions. Specifically, they help the body convert the macronutrients (carbohydrates, fats, and proteins) into energy that cells can use.

It is important to understand that B vitamins do not provide energy themselves. They are not a source of calories. Instead, they are essential helpers in the chemical reactions that release energy from the foods we eat.

flowchart LR
    A["Carbohydrates<br/>Fats<br/>Proteins"] -->|"B vitamins<br/>as coenzymes"| B["Energy Released<br/>(ATP)"]
    C["B1 — Thiamin"] -.->|"assists"| B
    D["B2 — Riboflavin"] -.->|"assists"| B
    E["B3 — Niacin"] -.->|"assists"| B

    style A fill:#e67e22,color:#fff
    style B fill:#27ae60,color:#fff
    style C fill:#1abc9c,color:#fff
    style D fill:#1abc9c,color:#fff
    style E fill:#1abc9c,color:#fff

Exam Tip: A common mistake is to say that B vitamins "give you energy." This is incorrect. B vitamins help release energy from food — they are involved in the process, but they are not an energy source themselves. Always use the phrase "release energy from carbohydrates/fats/proteins."

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Common Exam Mistakes