Nutrition Diet: What do the different letter vitamins do?

November 2, 2025 •

2 min read

According to the Third National Health and Nutrition Examination Survey, a significant portion of the U.S. population has insufficient vitamin D levels, highlighting the widespread need for nutritional awareness. Understanding what do the different letter vitamins do is crucial for maintaining optimal health, as each plays a unique and essential role in the body.

Quick Summary

This guide details the specific roles of the fat-soluble and water-soluble letter vitamins, explaining how they support energy metabolism, immune function, vision, bone health, and cell protection.

Key Points

Fat-Soluble vs. Water-Soluble: Vitamins are classified into fat-soluble (A, D, E, K) and water-soluble (B-complex, C), which affects how they are absorbed and stored in the body.
Vitamin A for Vision: Vitamin A is essential for healthy vision, particularly for sight in low light, and supports immune and skin health.
Vitamin D for Bones: Critical for calcium absorption, vitamin D is vital for building and maintaining strong bones and teeth.
B-Complex for Energy: The B vitamins work together as coenzymes to help the body convert food into energy, supporting metabolic functions.
Vitamin C and Immunity: Known for boosting the immune system, vitamin C is also necessary for collagen production, wound healing, and iron absorption.
Antioxidant Protection: Vitamins C and E are powerful antioxidants that protect the body's cells from damage caused by harmful free radicals.
Vitamin K and Blood Clotting: Without vitamin K, blood cannot clot properly, and it also plays a role in maintaining strong bones.

The Essentials of a Vitamin-Rich Diet

Vitamins are essential nutrients needed for various bodily functions and overall health. There are 13 essential vitamins, divided into fat-soluble and water-soluble categories based on their absorption and storage. A balanced diet is the best way to get enough of these vital nutrients.

Fat-Soluble Vitamins: A, D, E, and K

Fat-soluble vitamins are absorbed with fat and stored in the body's tissues. They don't need to be consumed daily, but taking too much can be harmful.

Vitamin A (Retinol, Carotenoids)

Functions: Important for vision, immune function, reproduction, and skin health.
Sources: Animal products like liver and eggs (retinol); colorful fruits and vegetables like carrots and spinach (carotenoids).

Vitamin D (Calciferol)

Functions: Aids calcium absorption for strong bones, and supports muscle, nerve, and immune function.
Sources: Sunlight exposure; fatty fish, egg yolks, and fortified foods.

Vitamin E (Tocopherol)

Functions: Acts as an antioxidant, protecting cells from damage; supports immune function and red blood cell formation.
Sources: Vegetable oils, nuts, seeds, and leafy greens.

Vitamin K (Phylloquinone, Menaquinones)

Functions: Essential for blood clotting and bone health.
Sources: Leafy greens (K1); gut bacteria, fermented foods, and some animal products (K2).

Water-Soluble Vitamins: The B-Complex and Vitamin C

Water-soluble vitamins are not stored in the body and are excreted in urine, so they need regular dietary intake.

B-Complex Vitamins

These eight vitamins are crucial for converting food into energy.

B1 (Thiamine): Energy conversion and nerve function.
B2 (Riboflavin): Growth, red blood cell production, energy release.
B3 (Niacin): Energy metabolism, healthy skin and nerves.
B5 (Pantothenic Acid): Food metabolism and hormone production.
B6 (Pyridoxine): Red blood cell formation, brain function, protein metabolism.
B7 (Biotin): Carbohydrate and protein metabolism.
B9 (Folate/Folic Acid): Red blood cell formation and DNA production.
B12 (Cobalamin): Metabolism, red blood cell formation, nervous system health.

Vitamin C (Ascorbic Acid)

Functions: Antioxidant, supports the immune system, essential for collagen production and iron absorption.
Sources: Citrus fruits, bell peppers, broccoli, and strawberries.

Comparing Fat-Soluble and Water-Soluble Vitamins


Feature	Fat-Soluble Vitamins (A, D, E, K)	Water-Soluble Vitamins (B-Complex, C)
Absorption	Require dietary fat.	Absorbed with water.
Storage	Stored in body tissues.	Not generally stored.
Risk of Toxicity	Higher risk with excess.	Lower risk due to excretion.
Frequency of Intake	Not needed daily.	Need regular consumption.
Examples	A, D, E, K.	B-complex, C.

Conclusion

Each vitamin plays a crucial role in maintaining health. While supplements can help with deficiencies, a varied diet is the best source. Consume fruits, vegetables, lean proteins, and fortified foods for a full range of vitamins. Consult a healthcare provider for personalized advice on vitamin intake or supplementation. Additional information on essential vitamins is available from Cleveland Clinic.

Frequently Asked Questions

Fat-soluble vitamins (A, D, E, and K) are stored in the body’s fatty tissues and liver, so they don't need to be consumed daily. Water-soluble vitamins (B-complex and C) are not stored and are flushed out in the urine, requiring regular intake through diet.

Vitamin A is most known for its role in vision, as it helps maintain healthy retinas and is essential for sight in low-light conditions. A deficiency can lead to night blindness.

The eight B vitamins act as coenzymes in energy metabolism, helping the body break down carbohydrates, proteins, and fats and convert them into fuel for cellular functions.

Vitamin D is crucial for bone health because it helps the body absorb calcium and phosphorus, the key minerals needed to build and maintain strong bones and teeth.

Symptoms of a vitamin deficiency vary depending on the specific vitamin but can include fatigue, hair loss, pale skin, muscle weakness, and in severe cases, more serious health issues like vision loss.

While many people can get all the vitamins they need from a balanced diet, some individuals, such as those with malabsorption issues or specific dietary restrictions, may require supplements. It is best to consult a healthcare provider to determine your needs.

Excellent food sources of vitamin C include citrus fruits, bell peppers, strawberries, broccoli, and kiwi. It helps support immune function and collagen production.