Nutrition - Humans » Vitamins A, C and D Functions

What you'll learn this session

Study time: 30 minutes

The essential functions of vitamins A, C and D in the human body
Food sources rich in these vital nutrients
Deficiency diseases and their symptoms
How these vitamins support growth, immunity and bone health
Daily requirements and absorption processes

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Introduction to Essential Vitamins

Vitamins are organic compounds that our bodies need in small amounts to function properly. Unlike macronutrients (carbohydrates, proteins and fats), we only need tiny quantities of vitamins, but they're absolutely crucial for good health. Today we'll explore three of the most important vitamins: A, C and D.

Key Definitions:

Vitamin: An organic compound required in small amounts for normal growth and development.
Deficiency disease: A condition caused by lack of a specific nutrient in the diet.
Fat-soluble vitamin: Vitamins that dissolve in fats and can be stored in body tissues (A and D).
Water-soluble vitamin: Vitamins that dissolve in water and cannot be stored long-term (C).

👁 Vitamin A - The Vision Vitamin

Vitamin A is essential for healthy vision, especially seeing in dim light. It also supports immune function and helps maintain healthy skin and mucous membranes that protect us from infections.

Vitamin A Functions and Sources

Vitamin A plays several vital roles in keeping our bodies healthy. It's particularly famous for its role in vision, but it does much more than help us see clearly.

Key Functions of Vitamin A

The primary functions of vitamin A include maintaining healthy vision, supporting immune system function and promoting proper cell growth and development. It's especially important during periods of rapid growth like childhood and pregnancy.

👀 Vision Support

Forms rhodopsin, a protein in the retina that helps us see in low light conditions. Without enough vitamin A, night blindness can develop.

🛡 Immune Function

Maintains the health of mucous membranes in the nose, throat and lungs, which act as barriers against infections.

🌱 Growth & Development

Essential for proper cell division and differentiation, particularly important for growing children and developing babies.

Best Food Sources: Liver, carrots, sweet potatoes, spinach, kale, eggs, dairy products and orange-coloured fruits like mangoes and apricots. The body can convert beta-carotene from orange vegetables into vitamin A.

Case Study: Night Blindness in Developing Countries

In parts of Africa and Asia, vitamin A deficiency affects millions of children. The World Health Organisation estimates that 250,000-500,000 children go blind each year due to vitamin A deficiency. Simple interventions like vitamin A supplements or growing vitamin A-rich vegetables can prevent this tragedy.

Vitamin C Functions and Sources

Vitamin C, also known as ascorbic acid, is probably the most famous vitamin. It's water-soluble, which means our bodies can't store it for long periods, so we need a regular supply from our diet.

🍊 Vitamin C - The Immunity Booster

Essential for collagen production, wound healing and maintaining a strong immune system. It also acts as a powerful antioxidant, protecting cells from damage.

Key Functions of Vitamin C

Vitamin C is involved in many important processes in the body. Its most crucial role is in making collagen, a protein that holds our tissues together.

🩸 Collagen Production

Essential for making collagen, which strengthens skin, blood vessels, bones and teeth. Without it, wounds heal poorly.

🛡 Immune Support

Helps white blood cells function properly and protects them from damage by harmful substances.

⚡ Iron Absorption

Improves the absorption of iron from plant foods, helping prevent iron deficiency anaemia.

Best Food Sources: Citrus fruits (oranges, lemons, limes), strawberries, kiwi fruit, bell peppers, broccoli, Brussels sprouts, tomatoes and potatoes. Fresh fruits and vegetables contain the most vitamin C.

Historical Case Study: Scurvy in Sailors

In the 18th century, sailors on long voyages often developed scurvy - a disease causing bleeding gums, loose teeth and poor wound healing. British naval surgeon James Lind discovered that citrus fruits prevented scurvy. This led to British sailors being called 'limeys' because they carried limes on ships!

Vitamin D Functions and Sources

Vitamin D is unique because our bodies can make it when our skin is exposed to sunlight. It's often called the 'sunshine vitamin' and is crucial for bone health.

☀ Vitamin D - The Sunshine Vitamin

Primarily responsible for calcium absorption and bone health. Made in the skin when exposed to sunlight, but also found in some foods.

Key Functions of Vitamin D

Vitamin D's main job is helping our bodies absorb calcium from food, which is essential for building and maintaining strong bones and teeth.

🦮 Calcium Absorption

Helps the intestines absorb calcium from food. Without vitamin D, we only absorb about 10-15% of dietary calcium.

🦷 Bone Health

Works with calcium and phosphorus to build and maintain strong bones and teeth throughout life.

💪 Muscle Function

Important for proper muscle function and may help reduce the risk of falls in older adults.

Sources: Sunlight exposure (15-30 minutes daily), fatty fish (salmon, mackerel, sardines), egg yolks, fortified cereals and milk and liver. In the UK, vitamin D supplements are recommended, especially during winter months.

Modern Challenge: Vitamin D Deficiency in the UK

Due to limited sunlight, especially in winter, many people in the UK have low vitamin D levels. This has led to a rise in rickets in children - a disease that causes soft, weak bones. The government now recommends vitamin D supplements for everyone during autumn and winter.

Deficiency Diseases and Prevention

When we don't get enough of these essential vitamins, specific deficiency diseases can develop. Understanding these helps us appreciate why a balanced diet is so important.

Vitamin Deficiency Diseases

Vitamin A Deficiency: Causes night blindness, dry eyes, increased infections and in severe cases, complete blindness. Children are particularly at risk.

Vitamin C Deficiency: Leads to scurvy, with symptoms including bleeding gums, loose teeth, poor wound healing, fatigue and joint pain.

Vitamin D Deficiency: Causes rickets in children (soft, deformed bones) and osteomalacia in adults (weak, painful bones). May also increase infection risk.

🏡 Prevention Tips

Eat a varied diet with plenty of fruits and vegetables, get regular sunlight exposure and consider supplements when recommended by healthcare professionals.

Daily Requirements and Practical Tips

Understanding how much of each vitamin we need helps us make better food choices. The amounts needed are small but crucial for good health.

Recommended Daily Amounts (for teenagers):

Vitamin A: 600-700 micrograms
Vitamin C: 40mg (about one orange)
Vitamin D: 10 micrograms (difficult to get from food alone)

Practical Tips:

Eat at least 5 portions of fruits and vegetables daily
Include orange/yellow vegetables for vitamin A
Have citrus fruits or berries for vitamin C
Spend time outdoors for vitamin D
Consider vitamin D supplements in winter
Don't overcook vegetables - this destroys vitamin C

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