Vitamins

Tiny molecules with enormous résumés: you need them in minuscule amounts, and you cannot do without them.

By Greg Goodwin · Published October 24, 2026

Cheat Sheet

Count: humans need 13 essential vitamins, and the body cannot make enough of most of them.
Fat-soluble set: vitamins A, D, E and K. The other nine (C and the eight B vitamins) are water-soluble.
Storage: fat-soluble vitamins are held in the liver and fatty tissue, so excess can build up; most water-soluble ones are not stored, with vitamin B12 a notable exception.
Name origin: Casimir Funk coined "vitamine" in 1912, from "vital" plus "amine"; the final e was later dropped.
Landmark trial: Scottish naval surgeon James Lind tested citrus against scurvy on sailors in 1747.
Upper limits: the NIH Office of Dietary Supplements lists some nutrients, such as vitamin B6 and zinc, with upper limits that should not be exceeded, while others have no identified limit.

The 60-Second Version

Vitamins are organic compounds your body needs in small quantities to run its chemistry, from turning food into energy to building bones, clotting blood, and keeping vision sharp. There are 13 essential ones. Four, vitamins A, D, E and K, dissolve in fat and can be stored in the body. The other nine, vitamin C and the eight B vitamins, dissolve in water and are mostly flushed out in urine rather than banked. Because the body makes little or none of most vitamins, they have to arrive through food, and the sources vary widely: leafy greens, citrus, dairy, eggs, fortified cereals, and sunlight for vitamin D. Too little can cause specific deficiency diseases. Too much of certain vitamins can cause harm too, which is why more is not automatically better. This page is general information, not medical advice.

The Long Version

How Vitamins Were Discovered

For centuries, sailors died of scurvy on long voyages. In 1747, the Scottish naval surgeon James Lind ran an early controlled comparison on board a ship and found that citrus fruit helped, long before anyone knew why. Around the turn of the twentieth century, researchers studying beriberi, including Christiaan Eijkman, found that something missing from polished rice caused the disease. In 1912 the Polish biochemist Casimir Funk proposed the name "vitamine" for these vital factors, believing they were amines. The final e was dropped once it became clear that not all of them were. Over the next few decades, the individual compounds were isolated one by one.

Two Families: Fat-Soluble and Water-Soluble

The sorting rule is simple. Vitamins A, D, E and K travel with dietary fat, are absorbed better alongside it, and are stored in the liver and fatty tissue. Because they linger, high intakes of these four are more likely to build up to harmful levels. The water-soluble group, vitamin C and the B vitamins (thiamin, riboflavin, niacin, pantothenic acid, B6, biotin, folate, and B12), is generally not stored for long, and excess tends to leave in urine. Vitamin B12 is the notable exception, since the liver holds a reserve of it. Water-soluble does not mean risk-free, though, and the NIH Office of Dietary Supplements notes that some, such as vitamin B6, have upper limits.

What They Actually Do

Vitamins are not fuel; they do not supply calories. Instead many act as helpers for enzymes, the proteins that speed up the body's chemical reactions. B vitamins help cells extract energy from carbohydrates, fats and protein. Vitamin K is needed for normal blood clotting. Vitamin A supports vision and the immune system, vitamin C is needed to make collagen, and vitamin D helps the body handle calcium for bone health. Folate is needed to make DNA, which is why it matters so much in early pregnancy. Each vitamin has its own job description, and no single one does everything.

Food, Fortification and Supplements

The NIH Office of Dietary Supplements advises that in most cases it is best to get nutrients from food first. Governments also add vitamins to common foods: the United States, for example, began requiring folic acid fortification of enriched grain products in 1998, and milk is commonly fortified with vitamin D. Recommended Dietary Allowances, or RDAs, cover nutrients from all sources, including food, not just pills. Supplements can be useful for people with particular needs or diagnosed deficiencies, but who needs what is a question for a clinician or registered dietitian, not an internet list.

Myths and Marketing

The vitamin aisle runs on big promises, and the evidence rarely matches. Megadoses are not a shortcut to better health, and the idea that water-soluble vitamins are always harmless is wrong, since some have identified upper limits. Supplements are also not the same as food: a diet rich in vegetables, fruit, whole grains and dairy delivers fiber and many other compounds that a capsule does not. Real deficiency diseases such as scurvy are uncommon in wealthy countries today, but certain groups, including people with absorption problems or very restricted diets, can run low on specific vitamins, and blood tests, not guesswork, are how that gets sorted out.

Why People Care

Vitamins are one of the most heavily marketed corners of health, so knowing the basics makes it easier to separate useful facts from hype. For most people, a varied diet covers the needs, and a clinician can advise on anything more. This is general information, not medical advice.

Glossary

Essential nutrient: A substance the body needs but cannot make in sufficient amounts, so it must come from food or supplements.
Fat-soluble vitamin: A vitamin (A, D, E or K) absorbed along with dietary fat and stored in body tissue.
Water-soluble vitamin: A vitamin (C or a B vitamin) that dissolves in water and is generally excreted in urine when in excess.
Deficiency disease: An illness caused by too little of a nutrient, such as scurvy (vitamin C) or beriberi (thiamin, vitamin B1).
RDA: Recommended Dietary Allowance, the average daily intake level considered sufficient for nearly all healthy people in a group, counting nutrients from all sources.

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