What Are Vitamins? A Plain-Language Guide to What They Do

What Do Vitamins Do?

Depending on the vitamin, it may help the body:

• Use energy from food
• Maintain normal vision
• Produce red blood cells
• Support bones, skin and nerves
• Help blood clot
• Support immune function
• Protect cells against certain types of damage

Vitamins do not contain calories, so they are not a direct source of energy. Some help the body process carbohydrates, fats and proteins, but the vitamin itself is not fuel.

How Many Vitamins Are There?

Scientists recognize 13 essential vitamins. Here, essential means the body needs them but cannot produce enough on its own.

• Vitamin A
• Vitamin C
• Vitamin D
• Vitamin E
• Vitamin K
• Vitamin B1, or thiamin
• Vitamin B2, or riboflavin
• Vitamin B3, or niacin
• Vitamin B5, or pantothenic acid
• Vitamin B6
• Vitamin B7, or biotin
• Vitamin B9, or folate
• Vitamin B12, or cobalamin

The B vitamins are separate vitamins that perform different functions. They share the letter B because of how scientists classified them historically, not because they are different strengths of the same vitamin.

Water-Soluble and Fat-Soluble Vitamins

Vitamins are divided into two groups based on how they dissolve and move through the body.

Water-Soluble Vitamins

Vitamin C and the eight B vitamins dissolve in water. The body generally stores limited amounts of most of them, so they usually need to be consumed regularly.

Vitamin B12 is an exception. Although it is water-soluble, the body can store substantial amounts, mainly in the liver.

Being water-soluble does not mean a vitamin is harmless at any dose. High amounts of some B vitamins can cause health problems.

Fat-Soluble Vitamins

Vitamins A, D, E and K dissolve in fat. The body can store them in the liver and body fat.

This storage provides a reserve for later use, but excessive amounts can accumulate. Taking more of a fat-soluble vitamin does not necessarily provide greater benefits and may become harmful.

Are Vitamins and Minerals the Same?

No. Both are nutrients, but they are different substances.

Vitamins are compounds that can change or break down because of heat, air or other conditions. Minerals are elements such as iron, calcium and magnesium. They retain their basic chemical identity.

Vitamins and minerals often work together. Vitamin D, for example, helps the body absorb calcium, while calcium helps build and maintain bones. They support related processes, but they cannot replace one another.

Supplements, Prescription Products and Vitamin Injections

A vitamin can be found in food, dietary supplements or medical products. These products may contain the same general vitamin but serve different purposes.

Dietary supplements include tablets, capsules, liquids, powders and gummies. A supplement label does not prove that someone needs the product or that taking more will provide an additional benefit.

Some vitamins are also available as prescription medications. A medical professional may recommend a specific form to treat a diagnosed deficiency or when the body has difficulty absorbing the vitamin during digestion.

An injection places the vitamin into the body without requiring it to pass through the digestive system first. This can be medically useful, but it does not mean injections are better for everyone.

Why Is Vitamin B12 Sometimes Injected?

Vitamin B12 helps produce healthy red blood cells, supports normal nerve function and participates in producing DNA, the material containing the body’s biological instructions.

Normal B12 absorption requires several steps involving the stomach and small intestine. Some people cannot absorb enough because of a medical condition, certain medications or surgery involving the digestive system.

A prescription B12 injection bypasses that absorption process. It may be used to treat a deficiency when there is an absorption problem or when a medical professional determines that an injection is appropriate.

B12 is frequently promoted as an energy booster. Correcting a deficiency may improve fatigue caused by that deficiency. Additional B12 has not been shown to provide more energy when someone already has enough.

Does Everyone Need Vitamin Supplements?

No. Many people can obtain the vitamins they need through a varied diet.

A supplement may be useful when someone has a diagnosed deficiency, difficulty absorbing nutrients, a restricted diet or another need identified by a qualified healthcare professional.

Symptoms such as fatigue are not limited to vitamin deficiencies. Assuming the cause based only on symptoms can lead someone to take an unnecessary product while overlooking the real problem.

Can You Take Too Many Vitamins?

Yes. Something being natural does not mean every amount is safe.

Excessive vitamin intake can cause side effects, interact with medications, alter laboratory test results or interfere with other nutrients. Fat-soluble vitamins can also accumulate in the body.

The appropriate amount depends on the vitamin, the person and why it is being used. A product showing a very high percentage of the Daily Value is not automatically more effective.

The Bottom Line

Vitamins help the body perform essential everyday processes, but taking more does not necessarily make the body work better.

Food, supplements, prescription products and injections can serve different purposes. Understanding those differences helps people ask better questions and make more informed decisions about vitamins.