What vitamins can humans not produce naturally?

November 21, 2025 •

3 min read

Humans, unlike most animals, are unable to synthesize vitamin C due to a genetic mutation, making dietary intake of this crucial nutrient essential for survival. This deficiency is a prime example of what vitamins can humans not produce, forcing us to rely on external sources to sustain vital bodily functions.

Quick Summary

The human body cannot synthesize most of the 13 essential vitamins and must acquire them through diet. This includes all B vitamins and vitamin C, as well as fat-soluble vitamins A, E, and K. Some can be produced in limited amounts, but rely on dietary intake for sufficient levels.

Key Points

Inability to Produce: Humans cannot synthesize vitamin C, vitamin B12, vitamin B1, B2, B5, B6, B7, B9, vitamin A, vitamin E, or vitamin K.
Vitamin C and Evolution: The inability to produce vitamin C is due to a non-functional gene for the enzyme L-gulonolactone oxidase.
B-Complex Dependence: All eight B vitamins must be obtained from dietary sources, with Vitamin B12 exclusively coming from bacteria via animal products or fortification.
Fat-Soluble Requirements: Vitamins A, E, and K are fat-soluble vitamins that are essential and must be absorbed through the diet.
The Sunshine Exception: Vitamin D can be produced in the skin from sun exposure, but dietary sources are still necessary for many to prevent deficiency.
Diet is Key: A balanced diet is crucial to acquire these essential vitamins, as excess water-soluble vitamins are not stored and are excreted from the body.

The Foundation of Human Nutrition: Essential Vitamins

A vitamin is an organic compound required as a vital nutrient that an organism cannot synthesize in sufficient quantities, and therefore must be obtained from its diet. The human body, while a marvel of biochemical engineering, is surprisingly dependent on external sources for the majority of its vitamin needs. This biological limitation means that without a balanced diet rich in fruits, vegetables, and other nutrient-dense foods, the risk of deficiency-related diseases is high.

The Water-Soluble Vitamins We Cannot Produce

Water-soluble vitamins are not stored in the body for long periods, with any excess excreted through urine, and must therefore be consumed regularly. Humans are entirely dependent on dietary intake for this group, which includes Vitamin C and the B-complex vitamins. The reasons for this inability are rooted in human evolution and genetic changes over millennia.

Vitamin C (Ascorbic Acid)

The inability to produce vitamin C is arguably the most well-known example of a human dietary requirement. Unlike most animals, humans lost the functional enzyme L-gulonolactone oxidase, which is necessary for the final step of vitamin C synthesis. A lack of vitamin C can lead to scurvy, a disease characterized by weakened connective tissue, hemorrhaging, and poor wound healing.

The B-Complex Vitamins

This group comprises eight distinct vitamins, all of which must be consumed through the diet as coenzymes for various metabolic processes.

Thiamine (B1): Essential for converting carbohydrates into energy.
Riboflavin (B2): Vital for energy production and cellular function.
Niacin (B3): While the body can synthesize some from the amino acid tryptophan, the amount is insufficient to meet demands, making dietary intake necessary.
Pantothenic Acid (B5): Crucial for fat and carbohydrate metabolism.
Pyridoxine (B6): Important for amino acid metabolism, red blood cell formation, and nervous system function.
Biotin (B7): A coenzyme for metabolizing proteins and carbohydrates.
Folate (B9): Works with vitamin B12 to form red blood cells and is essential for DNA production.
Cobalamin (B12): Not produced by the human body or by plants, B12 is exclusively synthesized by certain bacteria and must be obtained from animal products or fortified foods.

Fat-Soluble Vitamins Requiring Dietary Sources

Fat-soluble vitamins—A, E, and K—are absorbed with dietary fats and stored in the body's fatty tissues and liver. While this storage capacity reduces the need for daily consumption, they remain essential dietary components.

Vitamin A: Critical for vision, immune function, and cellular communication.
Vitamin E: Acts as an antioxidant, protecting cells from damage.
Vitamin K: Necessary for blood clotting and bone metabolism.

The Conditional Exception: Vitamin D

Vitamin D is a unique case among the essential vitamins. The body can produce it, but only with sufficient exposure to ultraviolet-B (UVB) radiation from the sun. Despite this capability, many people still require dietary sources or supplements due to factors like geographical location, limited sun exposure, and skin tone. In the absence of adequate sunlight, vitamin D becomes an essential nutrient that must be obtained from food sources like fatty fish or fortified products.

Fat-Soluble vs. Water-Soluble Vitamins: A Comparison


Feature	Fat-Soluble Vitamins (A, D, E, K)	Water-Soluble Vitamins (C, B-complex)
Human Production	Limited (Vitamin D) or none (A, E, K)	None (most B vitamins) or none at all (Vitamin C)
Storage in Body	Stored in liver and fatty tissues	Generally not stored, except for B12
Dietary Requirement	Required regularly, but not necessarily daily	Required on a regular basis to prevent depletion
Risk of Toxicity	Higher risk with excessive intake due to storage	Lower risk; excess is excreted
Absorption Mechanism	Absorbed with dietary fats	Absorbed directly into the bloodstream

Conclusion: The Critical Role of Diet

Understanding what vitamins can humans not produce is the first step toward building a healthy dietary plan. With the exception of vitamin D, and a limited amount of niacin, the human body is incapable of endogenous synthesis of the thirteen essential vitamins required for growth, development, and metabolic function. This biological reality underscores the importance of a varied and balanced diet that provides a consistent supply of these vital micronutrients. Regular consumption of foods rich in vitamins, and strategic supplementation when necessary, is the only way to ensure the body's continued health and resilience against deficiency-related illnesses.

For more detailed information on vitamin requirements and dietary sources, authoritative health websites such as the National Institutes of Health provide comprehensive guides on nutrient fact sheets.

Frequently Asked Questions

Humans are missing the functional gene for the enzyme L-gulonolactone oxidase, which is necessary to catalyze the final step in the synthesis of vitamin C.

No, the human body cannot produce B vitamins on its own. They must all be obtained from dietary sources. Vitamin B12, for example, is made by bacteria, not humans.

Vitamin D is considered an essential vitamin because while the body can produce it with sun exposure, many individuals do not get enough sunlight and must supplement through diet to maintain sufficient levels.

Water-soluble vitamins are not stored in large amounts in the body and any excess is excreted via urine, requiring a constant fresh supply. Fat-soluble vitamins can be stored in the liver and fatty tissues.

Food sources vary by vitamin. For example, vitamin C is found in citrus fruits and leafy greens, B12 is in animal products and fortified foods, and fat-soluble vitamins like A and K are in vegetables, eggs, and dairy.

Deficiencies can occur, leading to various health issues. For example, a lack of vitamin C causes scurvy, while a lack of B12 can lead to neurological problems and anemia.

Nearly all of the 13 essential vitamins (A, C, D, E, K, and 8 B-complex vitamins) must be acquired from the diet. The only exceptions are that some Vitamin D can be produced with sun exposure and limited Vitamin B3 can be synthesized from another amino acid.