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Introduction

Vitamins are organic compounds that the human body requires in small quantities for proper physiological function. Unlike macronutrients, vitamins are needed in (trace) amounts but play crucial roles in metabolism, immunity, and cellular repair. This article examines the 13 essential vitamins, their biological functions, dietary sources, and deficiency risks.

1. Water-Soluble Vitamins

(1) Vitamin B Complex

• B1 (Thiamine): Supports nerve function and carbohydrate metabolism
• B2 (Riboflavin): Important for energy production and skin health
• B3 (Niacin): Maintains cholesterol levels and nervous system
• B5 (Pantothenic Acid): Essential for coenzyme A synthesis
• B6 (Pyridoxine): Involved in amino acid metabolism
• B7 (Biotin): Supports hair, skin, and nail health
• B9 (Folate): Critical for DNA synthesis and fetal development
• B12 (Cobalamin): Necessary for red blood cell formation

(2) Vitamin C (Ascorbic Acid)

• Powerful antioxidant
• Collagen synthesis
• Immune system support

2. Fat-Soluble Vitamins

(1) Vitamin A (Retinoids)

• Vision maintenance
• Immune function
• Cellular growth

(2) Vitamin D (Calciferol)

• Calcium absorption
• Bone health
• Immune modulation

(3) Vitamin E (Tocopherols)

• Antioxidant protection
• Skin health
• Neurological function

(4) Vitamin K (Phylloquinone)

• Blood clotting
• Bone metabolism

3. Vitamin Functions and Sources

Table 1: Essential Vitamins and Their Primary Roles

Vitamin	Key Functions	Deficiency Symptoms
A	Vision, immunity	Night blindness, dry skin
B1	Energy metabolism	Beriberi, fatigue
B12	Nerve function	Anemia, neurological issues
C	Collagen synthesis	Scurvy, poor wound healing
D	Bone health	Rickets, osteoporosis
E	Antioxidant	Nerve damage, muscle weakness
K	Blood clotting	Excessive bleeding

4. Dietary Sources and Recommended Intake

Table 2: Vitamin-Rich Food Sources

Vitamin	Best Food Sources	Daily Adult Requirement
A	Carrots, sweet potatoes	700-900 mcg RAE
B12	Animal liver, fish	2.4 mcg
C	Citrus fruits, bell peppers	75-90 mg
D	Fatty fish, egg yolks	15 mcg (600 IU)
E	Nuts, seeds, vegetable oils	15 mg
K	Leafy greens, broccoli	90-120 mcg

5. Special Considerations

(1) At-Risk Groups

• Vegetarians/Vegans: May lack B12 and D
• Elderly: Often deficient in D and B12
• Pregnant women: Require extra folate and iron

(2) Supplementation Guidelines

• Most vitamins should come from food first
• Supplement only under professional guidance
• Fat-soluble vitamins (A,D,E,K) can accumulate to toxic levels

Conclusion

A balanced diet containing diverse whole foods typically provides all essential vitamins. Understanding each vitamin’s unique functions helps prevent deficiencies while avoiding excessive intake. Particular attention should be given to life-stage specific requirements and dietary restrictions that may necessitate supplementation under medical supervision.