Vitamin A (Retinol and Beta Carotene)

Introduction

Vitamin A, encompassing retinol and beta carotene, plays an essential role in maintaining overall health.

Sources of Vitamin A

Retinol (Pre-formed Vitamin A)

Found in animal-based foods like liver, fish oils, milk, cheese, and eggs.

Beta Carotene (Provitamin A)

Present in plant-based foods such as carrots, sweet potatoes, spinach, kale, and apricots.

Functions of Vitamin A

Vision: Essential for the production of rhodopsin, a protein necessary for low-light and colour vision.

Cell Growth and Differentiation: Plays a critical role in the normal formation and maintenance of the heart, lungs, kidneys, and other organs.

Skin and Mucous Membranes: Maintains the health and functionality of skin and mucous membranes.

Immune Function: Supports the immune system, enhancing the body's ability to fight infections.

Reproduction and Development: Vital for reproductive processes and embryonic development.

Effects of Vitamin A Deficiency

Night Blindness: The most common early symptom due to impaired rhodopsin production.

Xerophthalmia: A severe condition that can lead to blindness.

Skin Changes: Dry, itchy, and scaly skin due to decreased cell turnover.

Immune Deficiency: Increased susceptibility to infections.

Growth Impairment: In children, a deficiency can lead to stunted growth.

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Recommended Dietary Allowances (RDAs) for Vitamin A

Adult Men: 900 micrograms of retinol activity equivalents (RAE) per day. Adult Women: 700 micrograms RAE per day. Pregnancy and Lactation: Increased needs; up to 1200-1300 micrograms RAE per day.

Properties of Vitamin A

Fat-Soluble

Vitamin A is a fat-soluble vitamin, stored in the liver and requiring fats for absorption.

Stability

Retinol is sensitive to air and light exposure, whereas beta carotene is more stable.

Toxicity

Excess intake, particularly of retinol, can lead to hypervitaminosis A, causing liver damage and other health issues.

Exam Focus: Questions and Answers

1. Discuss the functions of Vitamin A in the human body.

Vitamin A is crucial for vision, especially in low light, as it aids in the production of rhodopsin. It also supports cell growth and differentiation, maintains skin and mucous membrane health, boosts immune function, and is essential for reproduction and development.

2. What are the effects of Vitamin A deficiency?

Vitamin A deficiency can lead to night blindness, xerophthalmia, skin changes like dryness and itching, increased susceptibility to infections, and in children, it can impair growth.

3. Describe the properties of Vitamin A.

Vitamin A is a fat-soluble vitamin, requiring dietary fats for its absorption. It's stored in the liver and sensitive to air and light exposure. Excessive intake, especially of retinol, can be toxic, leading to liver damage and other health problems.